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| author | Bill Wendling <isanbard@gmail.com> | 2012-08-08 08:21:24 +0000 |
|---|---|---|
| committer | Bill Wendling <isanbard@gmail.com> | 2012-08-08 08:21:24 +0000 |
| commit | 0bd3deeb292bbc6b58e091f6f1aade13976c4a8c (patch) | |
| tree | 84abb93ebc8498f19bfd37ca8561b0f57a9ce1a8 /docs | |
| parent | 45e9343e890327b42ab15df19e224cf64d67ccbb (diff) | |
Sphinxify the CommandLine document.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@161479 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/CommandLine.html | 1976 | ||||
| -rw-r--r-- | docs/CommandLine.rst | 1615 | ||||
| -rw-r--r-- | docs/programming.rst | 3 |
3 files changed, 1617 insertions, 1977 deletions
diff --git a/docs/CommandLine.html b/docs/CommandLine.html deleted file mode 100644 index a3743e159f..0000000000 --- a/docs/CommandLine.html +++ /dev/null @@ -1,1976 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> -<html> -<head> - <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> - <title>CommandLine 2.0 Library Manual</title> - <link rel="stylesheet" href="_static/llvm.css" type="text/css"> -</head> -<body> - -<h1> - CommandLine 2.0 Library Manual -</h1> - -<ol> - <li><a href="#introduction">Introduction</a></li> - - <li><a href="#quickstart">Quick Start Guide</a> - <ol> - <li><a href="#bool">Boolean Arguments</a></li> - <li><a href="#alias">Argument Aliases</a></li> - <li><a href="#onealternative">Selecting an alternative from a - set of possibilities</a></li> - <li><a href="#namedalternatives">Named alternatives</a></li> - <li><a href="#list">Parsing a list of options</a></li> - <li><a href="#bits">Collecting options as a set of flags</a></li> - <li><a href="#description">Adding freeform text to help output</a></li> - </ol></li> - - <li><a href="#referenceguide">Reference Guide</a> - <ol> - <li><a href="#positional">Positional Arguments</a> - <ul> - <li><a href="#--">Specifying positional options with hyphens</a></li> - <li><a href="#getPosition">Determining absolute position with - getPosition</a></li> - <li><a href="#cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> - modifier</a></li> - </ul></li> - - <li><a href="#storage">Internal vs External Storage</a></li> - - <li><a href="#attributes">Option Attributes</a></li> - - <li><a href="#modifiers">Option Modifiers</a> - <ul> - <li><a href="#hiding">Hiding an option from <tt>-help</tt> - output</a></li> - <li><a href="#numoccurrences">Controlling the number of occurrences - required and allowed</a></li> - <li><a href="#valrequired">Controlling whether or not a value must be - specified</a></li> - <li><a href="#formatting">Controlling other formatting options</a></li> - <li><a href="#misc">Miscellaneous option modifiers</a></li> - <li><a href="#response">Response files</a></li> - </ul></li> - - <li><a href="#toplevel">Top-Level Classes and Functions</a> - <ul> - <li><a href="#cl::ParseCommandLineOptions">The - <tt>cl::ParseCommandLineOptions</tt> function</a></li> - <li><a href="#cl::ParseEnvironmentOptions">The - <tt>cl::ParseEnvironmentOptions</tt> function</a></li> - <li><a href="#cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt> - function</a></li> - <li><a href="#cl::opt">The <tt>cl::opt</tt> class</a></li> - <li><a href="#cl::list">The <tt>cl::list</tt> class</a></li> - <li><a href="#cl::bits">The <tt>cl::bits</tt> class</a></li> - <li><a href="#cl::alias">The <tt>cl::alias</tt> class</a></li> - <li><a href="#cl::extrahelp">The <tt>cl::extrahelp</tt> class</a></li> - </ul></li> - - <li><a href="#builtinparsers">Builtin parsers</a> - <ul> - <li><a href="#genericparser">The Generic <tt>parser<t></tt> - parser</a></li> - <li><a href="#boolparser">The <tt>parser<bool></tt> - specialization</a></li> - <li><a href="#boolOrDefaultparser">The <tt>parser<boolOrDefault></tt> - specialization</a></li> - <li><a href="#stringparser">The <tt>parser<string></tt> - specialization</a></li> - <li><a href="#intparser">The <tt>parser<int></tt> - specialization</a></li> - <li><a href="#doubleparser">The <tt>parser<double></tt> and - <tt>parser<float></tt> specializations</a></li> - </ul></li> - </ol></li> - <li><a href="#extensionguide">Extension Guide</a> - <ol> - <li><a href="#customparser">Writing a custom parser</a></li> - <li><a href="#explotingexternal">Exploiting external storage</a></li> - <li><a href="#dynamicopts">Dynamically adding command line - options</a></li> - </ol></li> -</ol> - -<div class="doc_author"> - <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p> -</div> - -<!-- *********************************************************************** --> -<h2> - <a name="introduction">Introduction</a> -</h2> -<!-- *********************************************************************** --> - -<div> - -<p>This document describes the CommandLine argument processing library. It will -show you how to use it, and what it can do. The CommandLine library uses a -declarative approach to specifying the command line options that your program -takes. By default, these options declarations implicitly hold the value parsed -for the option declared (of course this <a href="#storage">can be -changed</a>).</p> - -<p>Although there are a <b>lot</b> of command line argument parsing libraries -out there in many different languages, none of them fit well with what I needed. -By looking at the features and problems of other libraries, I designed the -CommandLine library to have the following features:</p> - -<ol> -<li>Speed: The CommandLine library is very quick and uses little resources. The -parsing time of the library is directly proportional to the number of arguments -parsed, not the number of options recognized. Additionally, command line -argument values are captured transparently into user defined global variables, -which can be accessed like any other variable (and with the same -performance).</li> - -<li>Type Safe: As a user of CommandLine, you don't have to worry about -remembering the type of arguments that you want (is it an int? a string? a -bool? an enum?) and keep casting it around. Not only does this help prevent -error prone constructs, it also leads to dramatically cleaner source code.</li> - -<li>No subclasses required: To use CommandLine, you instantiate variables that -correspond to the arguments that you would like to capture, you don't subclass a -parser. This means that you don't have to write <b>any</b> boilerplate -code.</li> - -<li>Globally accessible: Libraries can specify command line arguments that are -automatically enabled in any tool that links to the library. This is possible -because the application doesn't have to keep a list of arguments to pass to -the parser. This also makes supporting <a href="#dynamicopts">dynamically -loaded options</a> trivial.</li> - -<li>Cleaner: CommandLine supports enum and other types directly, meaning that -there is less error and more security built into the library. You don't have to -worry about whether your integral command line argument accidentally got -assigned a value that is not valid for your enum type.</li> - -<li>Powerful: The CommandLine library supports many different types of -arguments, from simple <a href="#boolparser">boolean flags</a> to <a -href="#cl::opt">scalars arguments</a> (<a href="#stringparser">strings</a>, <a -href="#intparser">integers</a>, <a href="#genericparser">enums</a>, <a -href="#doubleparser">doubles</a>), to <a href="#cl::list">lists of -arguments</a>. This is possible because CommandLine is...</li> - -<li>Extensible: It is very simple to add a new argument type to CommandLine. -Simply specify the parser that you want to use with the command line option when -you declare it. <a href="#customparser">Custom parsers</a> are no problem.</li> - -<li>Labor Saving: The CommandLine library cuts down on the amount of grunt work -that you, the user, have to do. For example, it automatically provides a -<tt>-help</tt> option that shows the available command line options for your -tool. Additionally, it does most of the basic correctness checking for -you.</li> - -<li>Capable: The CommandLine library can handle lots of different forms of -options often found in real programs. For example, <a -href="#positional">positional</a> arguments, <tt>ls</tt> style <a -href="#cl::Grouping">grouping</a> options (to allow processing '<tt>ls --lad</tt>' naturally), <tt>ld</tt> style <a href="#cl::Prefix">prefix</a> -options (to parse '<tt>-lmalloc -L/usr/lib</tt>'), and <a -href="#cl::ConsumeAfter">interpreter style options</a>.</li> - -</ol> - -<p>This document will hopefully let you jump in and start using CommandLine in -your utility quickly and painlessly. Additionally it should be a simple -reference manual to figure out how stuff works. If it is failing in some area -(or you want an extension to the library), nag the author, <a -href="mailto:sabre@nondot.org">Chris Lattner</a>.</p> - -</div> - -<!-- *********************************************************************** --> -<h2> - <a name="quickstart">Quick Start Guide</a> -</h2> -<!-- *********************************************************************** --> - -<div> - -<p>This section of the manual runs through a simple CommandLine'ification of a -basic compiler tool. This is intended to show you how to jump into using the -CommandLine library in your own program, and show you some of the cool things it -can do.</p> - -<p>To start out, you need to include the CommandLine header file into your -program:</p> - -<div class="doc_code"><pre> - #include "llvm/Support/CommandLine.h" -</pre></div> - -<p>Additionally, you need to add this as the first line of your main -program:</p> - -<div class="doc_code"><pre> -int main(int argc, char **argv) { - <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv); - ... -} -</pre></div> - -<p>... which actually parses the arguments and fills in the variable -declarations.</p> - -<p>Now that you are ready to support command line arguments, we need to tell the -system which ones we want, and what type of arguments they are. The CommandLine -library uses a declarative syntax to model command line arguments with the -global variable declarations that capture the parsed values. This means that -for every command line option that you would like to support, there should be a -global variable declaration to capture the result. For example, in a compiler, -we would like to support the Unix-standard '<tt>-o <filename></tt>' option -to specify where to put the output. With the CommandLine library, this is -represented like this:</p> - -<a name="value_desc_example"></a> -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><string> OutputFilename("<i>o</i>", <a href="#cl::desc">cl::desc</a>("<i>Specify output filename</i>"), <a href="#cl::value_desc">cl::value_desc</a>("<i>filename</i>")); -</pre></div> - -<p>This declares a global variable "<tt>OutputFilename</tt>" that is used to -capture the result of the "<tt>o</tt>" argument (first parameter). We specify -that this is a simple scalar option by using the "<tt><a -href="#cl::opt">cl::opt</a></tt>" template (as opposed to the <a -href="#list">"<tt>cl::list</tt> template</a>), and tell the CommandLine library -that the data type that we are parsing is a string.</p> - -<p>The second and third parameters (which are optional) are used to specify what -to output for the "<tt>-help</tt>" option. In this case, we get a line that -looks like this:</p> - -<div class="doc_code"><pre> -USAGE: compiler [options] - -OPTIONS: - -help - display available options (-help-hidden for more) - <b>-o <filename> - Specify output filename</b> -</pre></div> - -<p>Because we specified that the command line option should parse using the -<tt>string</tt> data type, the variable declared is automatically usable as a -real string in all contexts that a normal C++ string object may be used. For -example:</p> - -<div class="doc_code"><pre> - ... - std::ofstream Output(OutputFilename.c_str()); - if (Output.good()) ... - ... -</pre></div> - -<p>There are many different options that you can use to customize the command -line option handling library, but the above example shows the general interface -to these options. The options can be specified in any order, and are specified -with helper functions like <a href="#cl::desc"><tt>cl::desc(...)</tt></a>, so -there are no positional dependencies to remember. The available options are -discussed in detail in the <a href="#referenceguide">Reference Guide</a>.</p> - -<p>Continuing the example, we would like to have our compiler take an input -filename as well as an output filename, but we do not want the input filename to -be specified with a hyphen (ie, not <tt>-filename.c</tt>). To support this -style of argument, the CommandLine library allows for <a -href="#positional">positional</a> arguments to be specified for the program. -These positional arguments are filled with command line parameters that are not -in option form. We use this feature like this:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>")); -</pre></div> - -<p>This declaration indicates that the first positional argument should be -treated as the input filename. Here we use the <tt><a -href="#cl::init">cl::init</a></tt> option to specify an initial value for the -command line option, which is used if the option is not specified (if you do not -specify a <tt><a href="#cl::init">cl::init</a></tt> modifier for an option, then -the default constructor for the data type is used to initialize the value). -Command line options default to being optional, so if we would like to require -that the user always specify an input filename, we would add the <tt><a -href="#cl::Required">cl::Required</a></tt> flag, and we could eliminate the -<tt><a href="#cl::init">cl::init</a></tt> modifier, like this:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <b><a href="#cl::Required">cl::Required</a></b>); -</pre></div> - -<p>Again, the CommandLine library does not require the options to be specified -in any particular order, so the above declaration is equivalent to:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><string> InputFilename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::Required">cl::Required</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>")); -</pre></div> - -<p>By simply adding the <tt><a href="#cl::Required">cl::Required</a></tt> flag, -the CommandLine library will automatically issue an error if the argument is not -specified, which shifts all of the command line option verification code out of -your application into the library. This is just one example of how using flags -can alter the default behaviour of the library, on a per-option basis. By -adding one of the declarations above, the <tt>-help</tt> option synopsis is now -extended to:</p> - -<div class="doc_code"><pre> -USAGE: compiler [options] <b><input file></b> - -OPTIONS: - -help - display available options (-help-hidden for more) - -o <filename> - Specify output filename -</pre></div> - -<p>... indicating that an input filename is expected.</p> - -<!-- ======================================================================= --> -<h3> - <a name="bool">Boolean Arguments</a> -</h3> - -<div> - -<p>In addition to input and output filenames, we would like the compiler example -to support three boolean flags: "<tt>-f</tt>" to force writing binary output to -a terminal, "<tt>--quiet</tt>" to enable quiet mode, and "<tt>-q</tt>" for -backwards compatibility with some of our users. We can support these by -declaring options of boolean type like this:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable binary output on terminals</i>")); -<a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>")); -<a href="#cl::opt">cl::opt</a><bool> Quiet2("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>"), <a href="#cl::Hidden">cl::Hidden</a>); -</pre></div> - -<p>This does what you would expect: it declares three boolean variables -("<tt>Force</tt>", "<tt>Quiet</tt>", and "<tt>Quiet2</tt>") to recognize these -options. Note that the "<tt>-q</tt>" option is specified with the "<a -href="#cl::Hidden"><tt>cl::Hidden</tt></a>" flag. This modifier prevents it -from being shown by the standard "<tt>-help</tt>" output (note that it is still -shown in the "<tt>-help-hidden</tt>" output).</p> - -<p>The CommandLine library uses a <a href="#builtinparsers">different parser</a> -for different data types. For example, in the string case, the argument passed -to the option is copied literally into the content of the string variable... we -obviously cannot do that in the boolean case, however, so we must use a smarter -parser. In the case of the boolean parser, it allows no options (in which case -it assigns the value of true to the variable), or it allows the values -"<tt>true</tt>" or "<tt>false</tt>" to be specified, allowing any of the -following inputs:</p> - -<div class="doc_code"><pre> - compiler -f # No value, 'Force' == true - compiler -f=true # Value specified, 'Force' == true - compiler -f=TRUE # Value specified, 'Force' == true - compiler -f=FALSE # Value specified, 'Force' == false -</pre></div> - -<p>... you get the idea. The <a href="#boolparser">bool parser</a> just turns -the string values into boolean values, and rejects things like '<tt>compiler --f=foo</tt>'. Similarly, the <a href="#doubleparser">float</a>, <a -href="#doubleparser">double</a>, and <a href="#intparser">int</a> parsers work -like you would expect, using the '<tt>strtol</tt>' and '<tt>strtod</tt>' C -library calls to parse the string value into the specified data type.</p> - -<p>With the declarations above, "<tt>compiler -help</tt>" emits this:</p> - -<div class="doc_code"><pre> -USAGE: compiler [options] <input file> - -OPTIONS: - <b>-f - Enable binary output on terminals</b> - -o - Override output filename - <b>-quiet - Don't print informational messages</b> - -help - display available options (-help-hidden for more) -</pre></div> - -<p>and "<tt>compiler -help-hidden</tt>" prints this:</p> - -<div class="doc_code"><pre> -USAGE: compiler [options] <input file> - -OPTIONS: - -f - Enable binary output on terminals - -o - Override output filename - <b>-q - Don't print informational messages</b> - -quiet - Don't print informational messages - -help - display available options (-help-hidden for more) -</pre></div> - -<p>This brief example has shown you how to use the '<tt><a -href="#cl::opt">cl::opt</a></tt>' class to parse simple scalar command line -arguments. In addition to simple scalar arguments, the CommandLine library also -provides primitives to support CommandLine option <a href="#alias">aliases</a>, -and <a href="#list">lists</a> of options.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="alias">Argument Aliases</a> -</h3> - -<div> - -<p>So far, the example works well, except for the fact that we need to check the -quiet condition like this now:</p> - -<div class="doc_code"><pre> -... - if (!Quiet && !Quiet2) printInformationalMessage(...); -... -</pre></div> - -<p>... which is a real pain! Instead of defining two values for the same -condition, we can use the "<tt><a href="#cl::alias">cl::alias</a></tt>" class to make the "<tt>-q</tt>" -option an <b>alias</b> for the "<tt>-quiet</tt>" option, instead of providing -a value itself:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><bool> Force ("<i>f</i>", <a href="#cl::desc">cl::desc</a>("<i>Overwrite output files</i>")); -<a href="#cl::opt">cl::opt</a><bool> Quiet ("<i>quiet</i>", <a href="#cl::desc">cl::desc</a>("<i>Don't print informational messages</i>")); -<a href="#cl::alias">cl::alias</a> QuietA("<i>q</i>", <a href="#cl::desc">cl::desc</a>("<i>Alias for -quiet</i>"), <a href="#cl::aliasopt">cl::aliasopt</a>(Quiet)); -</pre></div> - -<p>The third line (which is the only one we modified from above) defines a -"<tt>-q</tt>" alias that updates the "<tt>Quiet</tt>" variable (as specified by -the <tt><a href="#cl::aliasopt">cl::aliasopt</a></tt> modifier) whenever it is -specified. Because aliases do not hold state, the only thing the program has to -query is the <tt>Quiet</tt> variable now. Another nice feature of aliases is -that they automatically hide themselves from the <tt>-help</tt> output -(although, again, they are still visible in the <tt>-help-hidden -output</tt>).</p> - -<p>Now the application code can simply use:</p> - -<div class="doc_code"><pre> -... - if (!Quiet) printInformationalMessage(...); -... -</pre></div> - -<p>... which is much nicer! The "<tt><a href="#cl::alias">cl::alias</a></tt>" -can be used to specify an alternative name for any variable type, and has many -uses.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="onealternative">Selecting an alternative from a set of - possibilities</a> -</h3> - -<div> - -<p>So far we have seen how the CommandLine library handles builtin types like -<tt>std::string</tt>, <tt>bool</tt> and <tt>int</tt>, but how does it handle -things it doesn't know about, like enums or '<tt>int*</tt>'s?</p> - -<p>The answer is that it uses a table-driven generic parser (unless you specify -your own parser, as described in the <a href="#extensionguide">Extension -Guide</a>). This parser maps literal strings to whatever type is required, and -requires you to tell it what this mapping should be.</p> - -<p>Let's say that we would like to add four optimization levels to our -optimizer, using the standard flags "<tt>-g</tt>", "<tt>-O0</tt>", -"<tt>-O1</tt>", and "<tt>-O2</tt>". We could easily implement this with boolean -options like above, but there are several problems with this strategy:</p> - -<ol> -<li>A user could specify more than one of the options at a time, for example, -"<tt>compiler -O3 -O2</tt>". The CommandLine library would not be able to -catch this erroneous input for us.</li> - -<li>We would have to test 4 different variables to see which ones are set.</li> - -<li>This doesn't map to the numeric levels that we want... so we cannot easily -see if some level >= "<tt>-O1</tt>" is enabled.</li> - -</ol> - -<p>To cope with these problems, we can use an enum value, and have the -CommandLine library fill it in with the appropriate level directly, which is -used like this:</p> - -<div class="doc_code"><pre> -enum OptLevel { - g, O1, O2, O3 -}; - -<a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"), - <a href="#cl::values">cl::values</a>( - clEnumVal(g , "<i>No optimizations, enable debugging</i>"), - clEnumVal(O1, "<i>Enable trivial optimizations</i>"), - clEnumVal(O2, "<i>Enable default optimizations</i>"), - clEnumVal(O3, "<i>Enable expensive optimizations</i>"), - clEnumValEnd)); - -... - if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); -... -</pre></div> - -<p>This declaration defines a variable "<tt>OptimizationLevel</tt>" of the -"<tt>OptLevel</tt>" enum type. This variable can be assigned any of the values -that are listed in the declaration (Note that the declaration list must be -terminated with the "<tt>clEnumValEnd</tt>" argument!). The CommandLine -library enforces -that the user can only specify one of the options, and it ensure that only valid -enum values can be specified. The "<tt>clEnumVal</tt>" macros ensure that the -command line arguments matched the enum values. With this option added, our -help output now is:</p> - -<div class="doc_code"><pre> -USAGE: compiler [options] <input file> - -OPTIONS: - <b>Choose optimization level: - -g - No optimizations, enable debugging - -O1 - Enable trivial optimizations - -O2 - Enable default optimizations - -O3 - Enable expensive optimizations</b> - -f - Enable binary output on terminals - -help - display available options (-help-hidden for more) - -o <filename> - Specify output filename - -quiet - Don't print informational messages -</pre></div> - -<p>In this case, it is sort of awkward that flag names correspond directly to -enum names, because we probably don't want a enum definition named "<tt>g</tt>" -in our program. Because of this, we can alternatively write this example like -this:</p> - -<div class="doc_code"><pre> -enum OptLevel { - Debug, O1, O2, O3 -}; - -<a href="#cl::opt">cl::opt</a><OptLevel> OptimizationLevel(<a href="#cl::desc">cl::desc</a>("<i>Choose optimization level:</i>"), - <a href="#cl::values">cl::values</a>( - clEnumValN(Debug, "g", "<i>No optimizations, enable debugging</i>"), - clEnumVal(O1 , "<i>Enable trivial optimizations</i>"), - clEnumVal(O2 , "<i>Enable default optimizations</i>"), - clEnumVal(O3 , "<i>Enable expensive optimizations</i>"), - clEnumValEnd)); - -... - if (OptimizationLevel == Debug) outputDebugInfo(...); -... -</pre></div> - -<p>By using the "<tt>clEnumValN</tt>" macro instead of "<tt>clEnumVal</tt>", we -can directly specify the name that the flag should get. In general a direct -mapping is nice, but sometimes you can't or don't want to preserve the mapping, -which is when you would use it.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="namedalternatives">Named Alternatives</a> -</h3> - -<div> - -<p>Another useful argument form is a named alternative style. We shall use this -style in our compiler to specify different debug levels that can be used. -Instead of each debug level being its own switch, we want to support the -following options, of which only one can be specified at a time: -"<tt>--debug-level=none</tt>", "<tt>--debug-level=quick</tt>", -"<tt>--debug-level=detailed</tt>". To do this, we use the exact same format as -our optimization level flags, but we also specify an option name. For this -case, the code looks like this:</p> - -<div class="doc_code"><pre> -enum DebugLev { - nodebuginfo, quick, detailed -}; - -// Enable Debug Options to be specified on the command line -<a href="#cl::opt">cl::opt</a><DebugLev> DebugLevel("<i>debug_level</i>", <a href="#cl::desc">cl::desc</a>("<i>Set the debugging level:</i>"), - <a href="#cl::values">cl::values</a>( - clEnumValN(nodebuginfo, "none", "<i>disable debug information</i>"), - clEnumVal(quick, "<i>enable quick debug information</i>"), - clEnumVal(detailed, "<i>enable detailed debug information</i>"), - clEnumValEnd)); -</pre></div> - -<p>This definition defines an enumerated command line variable of type "<tt>enum -DebugLev</tt>", which works exactly the same way as before. The difference here -is just the interface exposed to the user of your program and the help output by -the "<tt>-help</tt>" option:</p> - -<div class="doc_code"><pre> -USAGE: compiler [options] <input file> - -OPTIONS: - Choose optimization level: - -g - No optimizations, enable debugging - -O1 - Enable trivial optimizations - -O2 - Enable default optimizations - -O3 - Enable expensive optimizations - <b>-debug_level - Set the debugging level: - =none - disable debug information - =quick - enable quick debug information - =detailed - enable detailed debug information</b> - -f - Enable binary output on terminals - -help - display available options (-help-hidden for more) - -o <filename> - Specify output filename - -quiet - Don't print informational messages -</pre></div> - -<p>Again, the only structural difference between the debug level declaration and -the optimization level declaration is that the debug level declaration includes -an option name (<tt>"debug_level"</tt>), which automatically changes how the -library processes the argument. The CommandLine library supports both forms so -that you can choose the form most appropriate for your application.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="list">Parsing a list of options</a> -</h3> - -<div> - -<p>Now that we have the standard run-of-the-mill argument types out of the way, -lets get a little wild and crazy. Lets say that we want our optimizer to accept -a <b>list</b> of optimizations to perform, allowing duplicates. For example, we -might want to run: "<tt>compiler -dce -constprop -inline -dce -strip</tt>". In -this case, the order of the arguments and the number of appearances is very -important. This is what the "<tt><a href="#cl::list">cl::list</a></tt>" -template is for. First, start by defining an enum of the optimizations that you -would like to perform:</p> - -<div class="doc_code"><pre> -enum Opts { - // 'inline' is a C++ keyword, so name it 'inlining' - dce, constprop, inlining, strip -}; -</pre></div> - -<p>Then define your "<tt><a href="#cl::list">cl::list</a></tt>" variable:</p> - -<div class="doc_code"><pre> -<a href="#cl::list">cl::list</a><Opts> OptimizationList(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"), - <a href="#cl::values">cl::values</a>( - clEnumVal(dce , "<i>Dead Code Elimination</i>"), - clEnumVal(constprop , "<i>Constant Propagation</i>"), - clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"), - clEnumVal(strip , "<i>Strip Symbols</i>"), - clEnumValEnd)); -</pre></div> - -<p>This defines a variable that is conceptually of the type -"<tt>std::vector<enum Opts></tt>". Thus, you can access it with standard -vector methods:</p> - -<div class="doc_code"><pre> - for (unsigned i = 0; i != OptimizationList.size(); ++i) - switch (OptimizationList[i]) - ... -</pre></div> - -<p>... to iterate through the list of options specified.</p> - -<p>Note that the "<tt><a href="#cl::list">cl::list</a></tt>" template is -completely general and may be used with any data types or other arguments that -you can use with the "<tt><a href="#cl::opt">cl::opt</a></tt>" template. One -especially useful way to use a list is to capture all of the positional -arguments together if there may be more than one specified. In the case of a -linker, for example, the linker takes several '<tt>.o</tt>' files, and needs to -capture them into a list. This is naturally specified as:</p> - -<div class="doc_code"><pre> -... -<a href="#cl::list">cl::list</a><std::string> InputFilenames(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<Input files>"), <a href="#cl::OneOrMore">cl::OneOrMore</a>); -... -</pre></div> - -<p>This variable works just like a "<tt>vector<string></tt>" object. As -such, accessing the list is simple, just like above. In this example, we used -the <tt><a href="#cl::OneOrMore">cl::OneOrMore</a></tt> modifier to inform the -CommandLine library that it is an error if the user does not specify any -<tt>.o</tt> files on our command line. Again, this just reduces the amount of -checking we have to do.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="bits">Collecting options as a set of flags</a> -</h3> - -<div> - -<p>Instead of collecting sets of options in a list, it is also possible to -gather information for enum values in a <b>bit vector</b>. The representation used by -the <a href="#bits"><tt>cl::bits</tt></a> class is an <tt>unsigned</tt> -integer. An enum value is represented by a 0/1 in the enum's ordinal value bit -position. 1 indicating that the enum was specified, 0 otherwise. As each -specified value is parsed, the resulting enum's bit is set in the option's bit -vector:</p> - -<div class="doc_code"><pre> - <i>bits</i> |= 1 << (unsigned)<i>enum</i>; -</pre></div> - -<p>Options that are specified multiple times are redundant. Any instances after -the first are discarded.</p> - -<p>Reworking the above list example, we could replace <a href="#list"> -<tt>cl::list</tt></a> with <a href="#bits"><tt>cl::bits</tt></a>:</p> - -<div class="doc_code"><pre> -<a href="#cl::bits">cl::bits</a><Opts> OptimizationBits(<a href="#cl::desc">cl::desc</a>("<i>Available Optimizations:</i>"), - <a href="#cl::values">cl::values</a>( - clEnumVal(dce , "<i>Dead Code Elimination</i>"), - clEnumVal(constprop , "<i>Constant Propagation</i>"), - clEnumValN(inlining, "<i>inline</i>", "<i>Procedure Integration</i>"), - clEnumVal(strip , "<i>Strip Symbols</i>"), - clEnumValEnd)); -</pre></div> - -<p>To test to see if <tt>constprop</tt> was specified, we can use the -<tt>cl:bits::isSet</tt> function:</p> - -<div class="doc_code"><pre> - if (OptimizationBits.isSet(constprop)) { - ... - } -</pre></div> - -<p>It's also possible to get the raw bit vector using the -<tt>cl::bits::getBits</tt> function:</p> - -<div class="doc_code"><pre> - unsigned bits = OptimizationBits.getBits(); -</pre></div> - -<p>Finally, if external storage is used, then the location specified must be of -<b>type</b> <tt>unsigned</tt>. In all other ways a <a -href="#bits"><tt>cl::bits</tt></a> option is equivalent to a <a -href="#list"> <tt>cl::list</tt></a> option.</p> - -</div> - - -<!-- ======================================================================= --> -<h3> - <a name="description">Adding freeform text to help output</a> -</h3> - -<div> - -<p>As our program grows and becomes more mature, we may decide to put summary -information about what it does into the help output. The help output is styled -to look similar to a Unix <tt>man</tt> page, providing concise information about -a program. Unix <tt>man</tt> pages, however often have a description about what -the program does. To add this to your CommandLine program, simply pass a third -argument to the <a -href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> -call in main. This additional argument is then printed as the overview -information for your program, allowing you to include any additional information -that you want. For example:</p> - -<div class="doc_code"><pre> -int main(int argc, char **argv) { - <a href="#cl::ParseCommandLineOptions">cl::ParseCommandLineOptions</a>(argc, argv, " CommandLine compiler example\n\n" - " This program blah blah blah...\n"); - ... -} -</pre></div> - -<p>would yield the help output:</p> - -<div class="doc_code"><pre> -<b>OVERVIEW: CommandLine compiler example - - This program blah blah blah...</b> - -USAGE: compiler [options] <input file> - -OPTIONS: - ... - -help - display available options (-help-hidden for more) - -o <filename> - Specify output filename -</pre></div> - -</div> - -</div> - -<!-- *********************************************************************** --> -<h2> - <a name="referenceguide">Reference Guide</a> -</h2> -<!-- *********************************************************************** --> - -<div> - -<p>Now that you know the basics of how to use the CommandLine library, this -section will give you the detailed information you need to tune how command line -options work, as well as information on more "advanced" command line option -processing capabilities.</p> - -<!-- ======================================================================= --> -<h3> - <a name="positional">Positional Arguments</a> -</h3> - -<div> - -<p>Positional arguments are those arguments that are not named, and are not -specified with a hyphen. Positional arguments should be used when an option is -specified by its position alone. For example, the standard Unix <tt>grep</tt> -tool takes a regular expression argument, and an optional filename to search -through (which defaults to standard input if a filename is not specified). -Using the CommandLine library, this would be specified as:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><string> Regex (<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><regular expression></i>"), <a href="#cl::Required">cl::Required</a>); -<a href="#cl::opt">cl::opt</a><string> Filename(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input file></i>"), <a href="#cl::init">cl::init</a>("<i>-</i>")); -</pre></div> - -<p>Given these two option declarations, the <tt>-help</tt> output for our grep -replacement would look like this:</p> - -<div class="doc_code"><pre> -USAGE: spiffygrep [options] <b><regular expression> <input file></b> - -OPTIONS: - -help - display available options (-help-hidden for more) -</pre></div> - -<p>... and the resultant program could be used just like the standard -<tt>grep</tt> tool.</p> - -<p>Positional arguments are sorted by their order of construction. This means -that command line options will be ordered according to how they are listed in a -.cpp file, but will not have an ordering defined if the positional arguments -are defined in multiple .cpp files. The fix for this problem is simply to -define all of your positional arguments in one .cpp file.</p> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="--">Specifying positional options with hyphens</a> -</h4> - -<div> - -<p>Sometimes you may want to specify a value to your positional argument that -starts with a hyphen (for example, searching for '<tt>-foo</tt>' in a file). At -first, you will have trouble doing this, because it will try to find an argument -named '<tt>-foo</tt>', and will fail (and single quotes will not save you). -Note that the system <tt>grep</tt> has the same problem:</p> - -<div class="doc_code"><pre> - $ spiffygrep '-foo' test.txt - Unknown command line argument '-foo'. Try: spiffygrep -help' - - $ grep '-foo' test.txt - grep: illegal option -- f - grep: illegal option -- o - grep: illegal option -- o - Usage: grep -hblcnsviw pattern file . . . -</pre></div> - -<p>The solution for this problem is the same for both your tool and the system -version: use the '<tt>--</tt>' marker. When the user specifies '<tt>--</tt>' on -the command line, it is telling the program that all options after the -'<tt>--</tt>' should be treated as positional arguments, not options. Thus, we -can use it like this:</p> - -<div class="doc_code"><pre> - $ spiffygrep -- -foo test.txt - ...output... -</pre></div> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="getPosition">Determining absolute position with getPosition()</a> -</h4> -<div> - <p>Sometimes an option can affect or modify the meaning of another option. For - example, consider <tt>gcc</tt>'s <tt>-x LANG</tt> option. This tells - <tt>gcc</tt> to ignore the suffix of subsequent positional arguments and force - the file to be interpreted as if it contained source code in language - <tt>LANG</tt>. In order to handle this properly, you need to know the - absolute position of each argument, especially those in lists, so their - interaction(s) can be applied correctly. This is also useful for options like - <tt>-llibname</tt> which is actually a positional argument that starts with - a dash.</p> - <p>So, generally, the problem is that you have two <tt>cl::list</tt> variables - that interact in some way. To ensure the correct interaction, you can use the - <tt>cl::list::getPosition(optnum)</tt> method. This method returns the - absolute position (as found on the command line) of the <tt>optnum</tt> - item in the <tt>cl::list</tt>.</p> - <p>The idiom for usage is like this:</p> - - <div class="doc_code"><pre> - static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); - static cl::list<std::string> Libraries("l", cl::ZeroOrMore); - - int main(int argc, char**argv) { - // ... - std::vector<std::string>::iterator fileIt = Files.begin(); - std::vector<std::string>::iterator libIt = Libraries.begin(); - unsigned libPos = 0, filePos = 0; - while ( 1 ) { - if ( libIt != Libraries.end() ) - libPos = Libraries.getPosition( libIt - Libraries.begin() ); - else - libPos = 0; - if ( fileIt != Files.end() ) - filePos = Files.getPosition( fileIt - Files.begin() ); - else - filePos = 0; - - if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) { - // Source File Is next - ++fileIt; - } - else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) { - // Library is next - ++libIt; - } - else - break; // we're done with the list - } - }</pre></div> - - <p>Note that, for compatibility reasons, the <tt>cl::opt</tt> also supports an - <tt>unsigned getPosition()</tt> option that will provide the absolute position - of that option. You can apply the same approach as above with a - <tt>cl::opt</tt> and a <tt>cl::list</tt> option as you can with two lists.</p> -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::ConsumeAfter">The <tt>cl::ConsumeAfter</tt> modifier</a> -</h4> - -<div> - -<p>The <tt>cl::ConsumeAfter</tt> <a href="#formatting">formatting option</a> is -used to construct programs that use "interpreter style" option processing. With -this style of option processing, all arguments specified after the last -positional argument are treated as special interpreter arguments that are not -interpreted by the command line argument.</p> - -<p>As a concrete example, lets say we are developing a replacement for the -standard Unix Bourne shell (<tt>/bin/sh</tt>). To run <tt>/bin/sh</tt>, first -you specify options to the shell itself (like <tt>-x</tt> which turns on trace -output), then you specify the name of the script to run, then you specify -arguments to the script. These arguments to the script are parsed by the Bourne -shell command line option processor, but are not interpreted as options to the -shell itself. Using the CommandLine library, we would specify this as:</p> - -<div class="doc_code"><pre> -<a href="#cl::opt">cl::opt</a><string> Script(<a href="#cl::Positional">cl::Positional</a>, <a href="#cl::desc">cl::desc</a>("<i><input script></i>"), <a href="#cl::init">cl::init</a>("-")); -<a href="#cl::list">cl::list</a><string> Argv(<a href="#cl::ConsumeAfter">cl::ConsumeAfter</a>, <a href="#cl::desc">cl::desc</a>("<i><program arguments>...</i>")); -<a href="#cl::opt">cl::opt</a><bool> Trace("<i>x</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable trace output</i>")); -</pre></div> - -<p>which automatically provides the help output:</p> - -<div class="doc_code"><pre> -USAGE: spiffysh [options] <b><input script> <program arguments>...</b> - -OPTIONS: - -help - display available options (-help-hidden for more) - <b>-x - Enable trace output</b> -</pre></div> - -<p>At runtime, if we run our new shell replacement as `<tt>spiffysh -x test.sh --a -x -y bar</tt>', the <tt>Trace</tt> variable will be set to true, the -<tt>Script</tt> variable will be set to "<tt>test.sh</tt>", and the -<tt>Argv</tt> list will contain <tt>["-a", "-x", "-y", "bar"]</tt>, because they -were specified after the last positional argument (which is the script -name).</p> - -<p>There are several limitations to when <tt>cl::ConsumeAfter</tt> options can -be specified. For example, only one <tt>cl::ConsumeAfter</tt> can be specified -per program, there must be at least one <a href="#positional">positional -argument</a> specified, there must not be any <a href="#cl::list">cl::list</a> -positional arguments, and the <tt>cl::ConsumeAfter</tt> option should be a <a -href="#cl::list">cl::list</a> option.</p> - -</div> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="storage">Internal vs External Storage</a> -</h3> - -<div> - -<p>By default, all command line options automatically hold the value that they -parse from the command line. This is very convenient in the common case, -especially when combined with the ability to define command line options in the -files that use them. This is called the internal storage model.</p> - -<p>Sometimes, however, it is nice to separate the command line option processing -code from the storage of the value parsed. For example, lets say that we have a -'<tt>-debug</tt>' option that we would like to use to enable debug information -across the entire body of our program. In this case, the boolean value -controlling the debug code should be globally accessible (in a header file, for -example) yet the command line option processing code should not be exposed to -all of these clients (requiring lots of .cpp files to #include -<tt>CommandLine.h</tt>).</p> - -<p>To do this, set up your .h file with your option, like this for example:</p> - -<div class="doc_code"> -<pre> -<i>// DebugFlag.h - Get access to the '-debug' command line option -// - -// DebugFlag - This boolean is set to true if the '-debug' command line option -// is specified. This should probably not be referenced directly, instead, use -// the DEBUG macro below. -//</i> -extern bool DebugFlag; - -<i>// DEBUG macro - This macro should be used by code to emit debug information. -// In the '-debug' option is specified on the command line, and if this is a -// debug build, then the code specified as the option to the macro will be -// executed. Otherwise it will not be.</i> -<span class="doc_hilite">#ifdef NDEBUG -#define DEBUG(X) -#else -#define DEBUG(X)</span> do { if (DebugFlag) { X; } } while (0) -<span class="doc_hilite">#endif</span> -</pre> -</div> - -<p>This allows clients to blissfully use the <tt>DEBUG()</tt> macro, or the -<tt>DebugFlag</tt> explicitly if they want to. Now we just need to be able to -set the <tt>DebugFlag</tt> boolean when the option is set. To do this, we pass -an additional argument to our command line argument processor, and we specify -where to fill in with the <a href="#cl::location">cl::location</a> -attribute:</p> - -<div class="doc_code"> -<pre> -bool DebugFlag; <i>// the actual value</i> -static <a href="#cl::opt">cl::opt</a><bool, true> <i>// The parser</i> -Debug("<i>debug</i>", <a href="#cl::desc">cl::desc</a>("<i>Enable debug output</i>"), <a href="#cl::Hidden">cl::Hidden</a>, <a href="#cl::location">cl::location</a>(DebugFlag)); -</pre> -</div> - -<p>In the above example, we specify "<tt>true</tt>" as the second argument to -the <tt><a href="#cl::opt">cl::opt</a></tt> template, indicating that the -template should not maintain a copy of the value itself. In addition to this, -we specify the <tt><a href="#cl::location">cl::location</a></tt> attribute, so -that <tt>DebugFlag</tt> is automatically set.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="attributes">Option Attributes</a> -</h3> - -<div> - -<p>This section describes the basic attributes that you can specify on -options.</p> - -<ul> - -<li>The option name attribute (which is required for all options, except <a -href="#positional">positional options</a>) specifies what the option name is. -This option is specified in simple double quotes: - -<pre> -<a href="#cl::opt">cl::opt</a><<b>bool</b>> Quiet("<i>quiet</i>"); -</pre> - -</li> - -<li><a name="cl::desc">The <b><tt>cl::desc</tt></b></a> attribute specifies a -description for the option to be shown in the <tt>-help</tt> output for the -program.</li> - -<li><a name="cl::value_desc">The <b><tt>cl::value_desc</tt></b></a> attribute -specifies a string that can be used to fine tune the <tt>-help</tt> output for -a command line option. Look <a href="#value_desc_example">here</a> for an -example.</li> - -<li><a name="cl::init">The <b><tt>cl::init</tt></b></a> attribute specifies an -initial value for a <a href="#cl::opt">scalar</a> option. If this attribute is -not specified then the command line option value defaults to the value created -by the default constructor for the type. <b>Warning</b>: If you specify both -<b><tt>cl::init</tt></b> and <b><tt>cl::location</tt></b> for an option, -you must specify <b><tt>cl::location</tt></b> first, so that when the -command-line parser sees <b><tt>cl::init</tt></b>, it knows where to put the -initial value. (You will get an error at runtime if you don't put them in -the right order.)</li> - -<li><a name="cl::location">The <b><tt>cl::location</tt></b></a> attribute where -to store the value for a parsed command line option if using external storage. -See the section on <a href="#storage">Internal vs External Storage</a> for more -information.</li> - -<li><a name="cl::aliasopt">The <b><tt>cl::aliasopt</tt></b></a> attribute -specifies which option a <tt><a href="#cl::alias">cl::alias</a></tt> option is -an alias for.</li> - -<li><a name="cl::values">The <b><tt>cl::values</tt></b></a> attribute specifies -the string-to-value mapping to be used by the generic parser. It takes a -<b>clEnumValEnd terminated</b> list of (option, value, description) triplets -that -specify the option name, the value mapped to, and the description shown in the -<tt>-help</tt> for the tool. Because the generic parser is used most -frequently with enum values, two macros are often useful: - -<ol> - -<li><a name="clEnumVal">The <b><tt>clEnumVal</tt></b></a> macro is used as a -nice simple way to specify a triplet for an enum. This macro automatically -makes the option name be the same as the enum name. The first option to the -macro is the enum, the second is the description for the command line -option.</li> - -<li><a name="clEnumValN">The <b><tt>clEnumValN</tt></b></a> macro is used to -specify macro options where the option name doesn't equal the enum name. For -this macro, the first argument is the enum value, the second is the flag name, -and the second is the description.</li> - -</ol> - -You will get a compile time error if you try to use cl::values with a parser -that does not support it.</li> - -<li><a name="cl::multi_val">The <b><tt>cl::multi_val</tt></b></a> -attribute specifies that this option takes has multiple values -(example: <tt>-sectalign segname sectname sectvalue</tt>). This -attribute takes one unsigned argument - the number of values for the -option. This attribute is valid only on <tt>cl::list</tt> options (and -will fail with compile error if you try to use it with other option -types). It is allowed to use all of the usual modifiers on -multi-valued options (besides <tt>cl::ValueDisallowed</tt>, -obviously).</li> - -</ul> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="modifiers">Option Modifiers</a> -</h3> - -<div> - -<p>Option modifiers are the flags and expressions that you pass into the -constructors for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a -href="#cl::list">cl::list</a></tt>. These modifiers give you the ability to -tweak how options are parsed and how <tt>-help</tt> output is generated to fit -your application well.</p> - -<p>These options fall into five main categories:</p> - -<ol> -<li><a href="#hiding">Hiding an option from <tt>-help</tt> output</a></li> -<li><a href="#numoccurrences">Controlling the number of occurrences - required and allowed</a></li> -<li><a href="#valrequired">Controlling whether or not a value must be - specified</a></li> -<li><a href="#formatting">Controlling other formatting options</a></li> -<li><a href="#misc">Miscellaneous option modifiers</a></li> -</ol> - -<p>It is not possible to specify two options from the same category (you'll get -a runtime error) to a single option, except for options in the miscellaneous -category. The CommandLine library specifies defaults for all of these settings -that are the most useful in practice and the most common, which mean that you -usually shouldn't have to worry about these.</p> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="hiding">Hiding an option from <tt>-help</tt> output</a> -</h4> - -<div> - -<p>The <tt>cl::NotHidden</tt>, <tt>cl::Hidden</tt>, and -<tt>cl::ReallyHidden</tt> modifiers are used to control whether or not an option -appears in the <tt>-help</tt> and <tt>-help-hidden</tt> output for the -compiled program:</p> - -<ul> - -<li><a name="cl::NotHidden">The <b><tt>cl::NotHidden</tt></b></a> modifier -(which is the default for <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a -href="#cl::list">cl::list</a></tt> options) indicates the option is to appear -in both help listings.</li> - -<li><a name="cl::Hidden">The <b><tt>cl::Hidden</tt></b></a> modifier (which is the -default for <tt><a href="#cl::alias">cl::alias</a></tt> options) indicates that -the option should not appear in the <tt>-help</tt> output, but should appear in -the <tt>-help-hidden</tt> output.</li> - -<li><a name="cl::ReallyHidden">The <b><tt>cl::ReallyHidden</tt></b></a> modifier -indicates that the option should not appear in any help output.</li> - -</ul> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="numoccurrences">Controlling the number of occurrences required and - allowed</a> -</h4> - -<div> - -<p>This group of options is used to control how many time an option is allowed -(or required) to be specified on the command line of your program. Specifying a -value for this setting allows the CommandLine library to do error checking for -you.</p> - -<p>The allowed values for this option group are:</p> - -<ul> - -<li><a name="cl::Optional">The <b><tt>cl::Optional</tt></b></a> modifier (which -is the default for the <tt><a href="#cl::opt">cl::opt</a></tt> and <tt><a -href="#cl::alias">cl::alias</a></tt> classes) indicates that your program will -allow either zero or one occurrence of the option to be specified.</li> - -<li><a name="cl::ZeroOrMore">The <b><tt>cl::ZeroOrMore</tt></b></a> modifier -(which is the default for the <tt><a href="#cl::list">cl::list</a></tt> class) -indicates that your program will allow the option to be specified zero or more -times.</li> - -<li><a name="cl::Required">The <b><tt>cl::Required</tt></b></a> modifier -indicates that the specified option must be specified exactly one time.</li> - -<li><a name="cl::OneOrMore">The <b><tt>cl::OneOrMore</tt></b></a> modifier -indicates that the option must be specified at least one time.</li> - -<li>The <b><tt>cl::ConsumeAfter</tt></b> modifier is described in the <a -href="#positional">Positional arguments section</a>.</li> - -</ul> - -<p>If an option is not specified, then the value of the option is equal to the -value specified by the <tt><a href="#cl::init">cl::init</a></tt> attribute. If -the <tt><a href="#cl::init">cl::init</a></tt> attribute is not specified, the -option value is initialized with the default constructor for the data type.</p> - -<p>If an option is specified multiple times for an option of the <tt><a -href="#cl::opt">cl::opt</a></tt> class, only the last value will be -retained.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="valrequired">Controlling whether or not a value must be specified</a> -</h4> - -<div> - -<p>This group of options is used to control whether or not the option allows a -value to be present. In the case of the CommandLine library, a value is either -specified with an equal sign (e.g. '<tt>-index-depth=17</tt>') or as a trailing -string (e.g. '<tt>-o a.out</tt>').</p> - -<p>The allowed values for this option group are:</p> - -<ul> - -<li><a name="cl::ValueOptional">The <b><tt>cl::ValueOptional</tt></b></a> modifier -(which is the default for <tt>bool</tt> typed options) specifies that it is -acceptable to have a value, or not. A boolean argument can be enabled just by -appearing on the command line, or it can have an explicit '<tt>-foo=true</tt>'. -If an option is specified with this mode, it is illegal for the value to be -provided without the equal sign. Therefore '<tt>-foo true</tt>' is illegal. To -get this behavior, you must use the <a -href="#cl::ValueRequired">cl::ValueRequired</a> modifier.</li> - -<li><a name="cl::ValueRequired">The <b><tt>cl::ValueRequired</tt></b></a> modifier -(which is the default for all other types except for <a -href="#onealternative">unnamed alternatives using the generic parser</a>) -specifies that a value must be provided. This mode informs the command line -library that if an option is not provides with an equal sign, that the next -argument provided must be the value. This allows things like '<tt>-o -a.out</tt>' to work.</li> - -<li><a name="cl::ValueDisallowed">The <b><tt>cl::ValueDisallowed</tt></b></a> -modifier (which is the default for <a href="#onealternative">unnamed -alternatives using the generic parser</a>) indicates that it is a runtime error -for the user to specify a value. This can be provided to disallow users from -providing options to boolean options (like '<tt>-foo=true</tt>').</li> - -</ul> - -<p>In general, the default values for this option group work just like you would -want them to. As mentioned above, you can specify the <a -href="#cl::ValueDisallowed">cl::ValueDisallowed</a> modifier to a boolean -argument to restrict your command line parser. These options are mostly useful -when <a href="#extensionguide">extending the library</a>.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="formatting">Controlling other formatting options</a> -</h4> - -<div> - -<p>The formatting option group is used to specify that the command line option -has special abilities and is otherwise different from other command line -arguments. As usual, you can only specify one of these arguments at most.</p> - -<ul> - -<li><a name="cl::NormalFormatting">The <b><tt>cl::NormalFormatting</tt></b></a> -modifier (which is the default all options) specifies that this option is -"normal".</li> - -<li><a name="cl::Positional">The <b><tt>cl::Positional</tt></b></a> modifier -specifies that this is a positional argument that does not have a command line -option associated with it. See the <a href="#positional">Positional -Arguments</a> section for more information.</li> - -<li>The <b><a href="#cl::ConsumeAfter"><tt>cl::ConsumeAfter</tt></a></b> modifier -specifies that this option is used to capture "interpreter style" arguments. See <a href="#cl::ConsumeAfter">this section for more information</a>.</li> - -<li><a name="cl::Prefix">The <b><tt>cl::Prefix</tt></b></a> modifier specifies -that this option prefixes its value. With 'Prefix' options, the equal sign does -not separate the value from the option name specified. Instead, the value is -everything after the prefix, including any equal sign if present. This is useful -for processing odd arguments like <tt>-lmalloc</tt> and <tt>-L/usr/lib</tt> in a -linker tool or <tt>-DNAME=value</tt> in a compiler tool. Here, the -'<tt>l</tt>', '<tt>D</tt>' and '<tt>L</tt>' options are normal string (or list) -options, that have the <b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> -modifier added to allow the CommandLine library to recognize them. Note that -<b><tt><a href="#cl::Prefix">cl::Prefix</a></tt></b> options must not have the -<b><tt><a href="#cl::ValueDisallowed">cl::ValueDisallowed</a></tt></b> modifier -specified.</li> - -<li><a name="cl::Grouping">The <b><tt>cl::Grouping</tt></b></a> modifier is used -to implement Unix-style tools (like <tt>ls</tt>) that have lots of single letter -arguments, but only require a single dash. For example, the '<tt>ls -labF</tt>' -command actually enables four different options, all of which are single -letters. Note that <b><tt><a href="#cl::Grouping">cl::Grouping</a></tt></b> -options cannot have values.</li> - -</ul> - -<p>The CommandLine library does not restrict how you use the <b><tt><a -href="#cl::Prefix">cl::Prefix</a></tt></b> or <b><tt><a -href="#cl::Grouping">cl::Grouping</a></tt></b> modifiers, but it is possible to -specify ambiguous argument settings. Thus, it is possible to have multiple -letter options that are prefix or grouping options, and they will still work as -designed.</p> - -<p>To do this, the CommandLine library uses a greedy algorithm to parse the -input option into (potentially multiple) prefix and grouping options. The -strategy basically looks like this:</p> - -<div class="doc_code"><tt>parse(string OrigInput) {</tt> - -<ol> -<li><tt>string input = OrigInput;</tt> -<li><tt>if (isOption(input)) return getOption(input).parse();</tt> <i>// Normal option</i> -<li><tt>while (!isOption(input) && !input.empty()) input.pop_back();</tt> <i>// Remove the last letter</i> -<li><tt>if (input.empty()) return error();</tt> <i>// No matching option</i> -<li><tt>if (getOption(input).isPrefix())<br> - return getOption(input).parse(input);</tt> -<li><tt>while (!input.empty()) { <i>// Must be grouping options</i><br> - getOption(input).parse();<br> - OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length());<br> - input = OrigInput;<br> - while (!isOption(input) && !input.empty()) input.pop_back();<br> -}</tt> -<li><tt>if (!OrigInput.empty()) error();</tt></li> -</ol> - -<p><tt>}</tt></p> -</div> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="misc">Miscellaneous option modifiers</a> -</h4> - -<div> - -<p>The miscellaneous option modifiers are the only flags where you can specify -more than one flag from the set: they are not mutually exclusive. These flags -specify boolean properties that modify the option.</p> - -<ul> - -<li><a name="cl::CommaSeparated">The <b><tt>cl::CommaSeparated</tt></b></a> modifier -indicates that any commas specified for an option's value should be used to -split the value up into multiple values for the option. For example, these two -options are equivalent when <tt>cl::CommaSeparated</tt> is specified: -"<tt>-foo=a -foo=b -foo=c</tt>" and "<tt>-foo=a,b,c</tt>". This option only -makes sense to be used in a case where the option is allowed to accept one or -more values (i.e. it is a <a href="#cl::list">cl::list</a> option).</li> - -<li><a name="cl::PositionalEatsArgs">The -<b><tt>cl::PositionalEatsArgs</tt></b></a> modifier (which only applies to -positional arguments, and only makes sense for lists) indicates that positional -argument should consume any strings after it (including strings that start with -a "-") up until another recognized positional argument. For example, if you -have two "eating" positional arguments, "<tt>pos1</tt>" and "<tt>pos2</tt>", the -string "<tt>-pos1 -foo -bar baz -pos2 -bork</tt>" would cause the "<tt>-foo -bar --baz</tt>" strings to be applied to the "<tt>-pos1</tt>" option and the -"<tt>-bork</tt>" string to be applied to the "<tt>-pos2</tt>" option.</li> - -<li><a name="cl::Sink">The <b><tt>cl::Sink</tt></b></a> modifier is -used to handle unknown options. If there is at least one option with -<tt>cl::Sink</tt> modifier specified, the parser passes -unrecognized option strings to it as values instead of signaling an -error. As with <tt>cl::CommaSeparated</tt>, this modifier -only makes sense with a <a href="#cl::list">cl::list</a> option.</li> - -</ul> - -<p>So far, these are the only three miscellaneous option modifiers.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="response">Response files</a> -</h4> - -<div> - -<p>Some systems, such as certain variants of Microsoft Windows and -some older Unices have a relatively low limit on command-line -length. It is therefore customary to use the so-called 'response -files' to circumvent this restriction. These files are mentioned on -the command-line (using the "@file") syntax. The program reads these -files and inserts the contents into argv, thereby working around the -command-line length limits. Response files are enabled by an optional -fourth argument to -<a href="#cl::ParseEnvironmentOptions"><tt>cl::ParseEnvironmentOptions</tt></a> -and -<a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>. -</p> - -</div> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="toplevel">Top-Level Classes and Functions</a> -</h3> - -<div> - -<p>Despite all of the built-in flexibility, the CommandLine option library -really only consists of one function (<a -href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>) -and three main classes: <a href="#cl::opt"><tt>cl::opt</tt></a>, <a -href="#cl::list"><tt>cl::list</tt></a>, and <a -href="#cl::alias"><tt>cl::alias</tt></a>. This section describes these three -classes in detail.</p> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::ParseCommandLineOptions">The <tt>cl::ParseCommandLineOptions</tt> - function</a> -</h4> - -<div> - -<p>The <tt>cl::ParseCommandLineOptions</tt> function is designed to be called -directly from <tt>main</tt>, and is used to fill in the values of all of the -command line option variables once <tt>argc</tt> and <tt>argv</tt> are -available.</p> - -<p>The <tt>cl::ParseCommandLineOptions</tt> function requires two parameters -(<tt>argc</tt> and <tt>argv</tt>), but may also take an optional third parameter -which holds <a href="#description">additional extra text</a> to emit when the -<tt>-help</tt> option is invoked, and a fourth boolean parameter that enables -<a href="#response">response files</a>.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::ParseEnvironmentOptions">The <tt>cl::ParseEnvironmentOptions</tt> - function</a> -</h4> - -<div> - -<p>The <tt>cl::ParseEnvironmentOptions</tt> function has mostly the same effects -as <a -href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>, -except that it is designed to take values for options from an environment -variable, for those cases in which reading the command line is not convenient or -desired. It fills in the values of all the command line option variables just -like <a -href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a> -does.</p> - -<p>It takes four parameters: the name of the program (since <tt>argv</tt> may -not be available, it can't just look in <tt>argv[0]</tt>), the name of the -environment variable to examine, the optional -<a href="#description">additional extra text</a> to emit when the -<tt>-help</tt> option is invoked, and the boolean -switch that controls whether <a href="#response">response files</a> -should be read.</p> - -<p><tt>cl::ParseEnvironmentOptions</tt> will break the environment -variable's value up into words and then process them using -<a href="#cl::ParseCommandLineOptions"><tt>cl::ParseCommandLineOptions</tt></a>. -<b>Note:</b> Currently <tt>cl::ParseEnvironmentOptions</tt> does not support -quoting, so an environment variable containing <tt>-option "foo bar"</tt> will -be parsed as three words, <tt>-option</tt>, <tt>"foo</tt>, and <tt>bar"</tt>, -which is different from what you would get from the shell with the same -input.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::SetVersionPrinter">The <tt>cl::SetVersionPrinter</tt> - function</a> -</h4> - -<div> - -<p>The <tt>cl::SetVersionPrinter</tt> function is designed to be called -directly from <tt>main</tt> and <i>before</i> -<tt>cl::ParseCommandLineOptions</tt>. Its use is optional. It simply arranges -for a function to be called in response to the <tt>--version</tt> option instead -of having the <tt>CommandLine</tt> library print out the usual version string -for LLVM. This is useful for programs that are not part of LLVM but wish to use -the <tt>CommandLine</tt> facilities. Such programs should just define a small -function that takes no arguments and returns <tt>void</tt> and that prints out -whatever version information is appropriate for the program. Pass the address -of that function to <tt>cl::SetVersionPrinter</tt> to arrange for it to be -called when the <tt>--version</tt> option is given by the user.</p> - -</div> -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::opt">The <tt>cl::opt</tt> class</a> -</h4> - -<div> - -<p>The <tt>cl::opt</tt> class is the class used to represent scalar command line -options, and is the one used most of the time. It is a templated class which -can take up to three arguments (all except for the first have default values -though):</p> - -<div class="doc_code"><pre> -<b>namespace</b> cl { - <b>template</b> <<b>class</b> DataType, <b>bool</b> ExternalStorage = <b>false</b>, - <b>class</b> ParserClass = parser<DataType> > - <b>class</b> opt; -} -</pre></div> - -<p>The first template argument specifies what underlying data type the command -line argument is, and is used to select a default parser implementation. The -second template argument is used to specify whether the option should contain -the storage for the option (the default) or whether external storage should be -used to contain the value parsed for the option (see <a href="#storage">Internal -vs External Storage</a> for more information).</p> - -<p>The third template argument specifies which parser to use. The default value -selects an instantiation of the <tt>parser</tt> class based on the underlying -data type of the option. In general, this default works well for most -applications, so this option is only used when using a <a -href="#customparser">custom parser</a>.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::list">The <tt>cl::list</tt> class</a> -</h4> - -<div> - -<p>The <tt>cl::list</tt> class is the class used to represent a list of command -line options. It too is a templated class which can take up to three -arguments:</p> - -<div class="doc_code"><pre> -<b>namespace</b> cl { - <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, - <b>class</b> ParserClass = parser<DataType> > - <b>class</b> list; -} -</pre></div> - -<p>This class works the exact same as the <a -href="#cl::opt"><tt>cl::opt</tt></a> class, except that the second argument is -the <b>type</b> of the external storage, not a boolean value. For this class, -the marker type '<tt>bool</tt>' is used to indicate that internal storage should -be used.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::bits">The <tt>cl::bits</tt> class</a> -</h4> - -<div> - -<p>The <tt>cl::bits</tt> class is the class used to represent a list of command -line options in the form of a bit vector. It is also a templated class which -can take up to three arguments:</p> - -<div class="doc_code"><pre> -<b>namespace</b> cl { - <b>template</b> <<b>class</b> DataType, <b>class</b> Storage = <b>bool</b>, - <b>class</b> ParserClass = parser<DataType> > - <b>class</b> bits; -} -</pre></div> - -<p>This class works the exact same as the <a -href="#cl::opt"><tt>cl::lists</tt></a> class, except that the second argument -must be of <b>type</b> <tt>unsigned</tt> if external storage is used.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::alias">The <tt>cl::alias</tt> class</a> -</h4> - -<div> - -<p>The <tt>cl::alias</tt> class is a nontemplated class that is used to form -aliases for other arguments.</p> - -<div class="doc_code"><pre> -<b>namespace</b> cl { - <b>class</b> alias; -} -</pre></div> - -<p>The <a href="#cl::aliasopt"><tt>cl::aliasopt</tt></a> attribute should be -used to specify which option this is an alias for. Alias arguments default to -being <a href="#cl::Hidden">Hidden</a>, and use the aliased options parser to do -the conversion from string to data.</p> - -</div> - -<!-- _______________________________________________________________________ --> -<h4> - <a name="cl::extrahelp">The <tt>cl::extrahelp</tt> class</a> -</h4> - -<div> - -<p>The <tt>cl::extrahelp</tt> class is a nontemplated class that allows extra -help text to be printed out for the <tt>-help</tt> option.</p> - -<div class="doc_code"><pre> -<b>namespace</b> cl { - <b>struct</b> extrahelp; -} -</pre></div> - -<p>To use the extrahelp, simply construct one with a <tt>const char*</tt> -parameter to the constructor. The text passed to the constructor will be printed -at the bottom of the help message, verbatim. Note that multiple -<tt>cl::extrahelp</tt> <b>can</b> be used, but this practice is discouraged. If -your tool needs to print additional help information, put all that help into a -single <tt>cl::extrahelp</tt> instance.</p> -<p>For example:</p> -<div class="doc_code"><pre> - cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); -</pre></div> -</div> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="builtinparsers">Builtin parsers</a> -</h3> - -<div> - -<p>Parsers control how the string value taken from the command line is -translated into a typed value, suitable for use in a C++ program. By default, -the CommandLine library uses an instance of <tt>parser<type></tt> if the -command line option specifies that it uses values of type '<tt>type</tt>'. -Because of this, custom option processing is specified with specializations of -the '<tt>parser</tt>' class.</p> - -<p>The CommandLine library provides the following builtin parser -specializations, which are sufficient for most applications. It can, however, -also be extended to work with new data types and new ways of interpreting the -same data. See the <a href="#customparser">Writing a Custom Parser</a> for more -details on this type of library extension.</p> - -<ul> - -<li><a name="genericparser">The <b>generic <tt>parser<t></tt> parser</b></a> -can be used to map strings values to any data type, through the use of the <a -href="#cl::values">cl::values</a> property, which specifies the mapping -information. The most common use of this parser is for parsing enum values, -which allows you to use the CommandLine library for all of the error checking to -make sure that only valid enum values are specified (as opposed to accepting -arbitrary strings). Despite this, however, the generic parser class can be used -for any data type.</li> - -<li><a name="boolparser">The <b><tt>parser<bool></tt> specialization</b></a> -is used to convert boolean strings to a boolean value. Currently accepted -strings are "<tt>true</tt>", "<tt>TRUE</tt>", "<tt>True</tt>", "<tt>1</tt>", -"<tt>false</tt>", "<tt>FALSE</tt>", "<tt>False</tt>", and "<tt>0</tt>".</li> - -<li><a name="boolOrDefaultparser">The <b><tt>parser<boolOrDefault></tt> - specialization</b></a> is used for cases where the value is boolean, -but we also need to know whether the option was specified at all. boolOrDefault -is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. This parser accepts -the same strings as <b><tt>parser<bool></tt></b>.</li> - -<li><a name="stringparser">The <b><tt>parser<string></tt> -specialization</b></a> simply stores the parsed string into the string value -specified. No conversion or modification of the data is performed.</li> - -<li><a name="intparser">The <b><tt>parser<int></tt> specialization</b></a> -uses the C <tt>strtol</tt> function to parse the string input. As such, it will -accept a decimal number (with an optional '+' or '-' prefix) which must start -with a non-zero digit. It accepts octal numbers, which are identified with a -'<tt>0</tt>' prefix digit, and hexadecimal numbers with a prefix of -'<tt>0x</tt>' or '<tt>0X</tt>'.</li> - -<li><a name="doubleparser">The <b><tt>parser<double></tt></b></a> and -<b><tt>parser<float></tt> specializations</b> use the standard C -<tt>strtod</tt> function to convert floating point strings into floating point -values. As such, a broad range of string formats is supported, including -exponential notation (ex: <tt>1.7e15</tt>) and properly supports locales. -</li> - -</ul> - -</div> - -</div> - -<!-- *********************************************************************** --> -<h2> - <a name="extensionguide">Extension Guide</a> -</h2> -<!-- *********************************************************************** --> - -<div> - -<p>Although the CommandLine library has a lot of functionality built into it -already (as discussed previously), one of its true strengths lie in its -extensibility. This section discusses how the CommandLine library works under -the covers and illustrates how to do some simple, common, extensions.</p> - -<!-- ======================================================================= --> -<h3> - <a name="customparser">Writing a custom parser</a> -</h3> - -<div> - -<p>One of the simplest and most common extensions is the use of a custom parser. -As <a href="#builtinparsers">discussed previously</a>, parsers are the portion -of the CommandLine library that turns string input from the user into a -particular parsed data type, validating the input in the process.</p> - -<p>There are two ways to use a new parser:</p> - -<ol> - -<li> - -<p>Specialize the <a href="#genericparser"><tt>cl::parser</tt></a> template for -your custom data type.<p> - -<p>This approach has the advantage that users of your custom data type will -automatically use your custom parser whenever they define an option with a value -type of your data type. The disadvantage of this approach is that it doesn't -work if your fundamental data type is something that is already supported.</p> - -</li> - -<li> - -<p>Write an independent class, using it explicitly from options that need -it.</p> - -<p>This approach works well in situations where you would line to parse an -option using special syntax for a not-very-special data-type. The drawback of -this approach is that users of your parser have to be aware that they are using -your parser instead of the builtin ones.</p> - -</li> - -</ol> - -<p>To guide the discussion, we will discuss a custom parser that accepts file -sizes, specified with an optional unit after the numeric size. For example, we -would like to parse "102kb", "41M", "1G" into the appropriate integer value. In -this case, the underlying data type we want to parse into is -'<tt>unsigned</tt>'. We choose approach #2 above because we don't want to make -this the default for all <tt>unsigned</tt> options.</p> - -<p>To start out, we declare our new <tt>FileSizeParser</tt> class:</p> - -<div class="doc_code"><pre> -<b>struct</b> FileSizeParser : <b>public</b> cl::basic_parser<<b>unsigned</b>> { - <i>// parse - Return true on error.</i> - <b>bool</b> parse(cl::Option &O, <b>const char</b> *ArgName, <b>const</b> std::string &ArgValue, - <b>unsigned</b> &Val); -}; -</pre></div> - -<p>Our new class inherits from the <tt>cl::basic_parser</tt> template class to -fill in the default, boiler plate code for us. We give it the data type that -we parse into, the last argument to the <tt>parse</tt> method, so that clients of -our custom parser know what object type to pass in to the parse method. (Here we -declare that we parse into '<tt>unsigned</tt>' variables.)</p> - -<p>For most purposes, the only method that must be implemented in a custom -parser is the <tt>parse</tt> method. The <tt>parse</tt> method is called -whenever the option is invoked, passing in the option itself, the option name, -the string to parse, and a reference to a return value. If the string to parse -is not well-formed, the parser should output an error message and return true. -Otherwise it should return false and set '<tt>Val</tt>' to the parsed value. In -our example, we implement <tt>parse</tt> as:</p> - -<div class="doc_code"><pre> -<b>bool</b> FileSizeParser::parse(cl::Option &O, <b>const char</b> *ArgName, - <b>const</b> std::string &Arg, <b>unsigned</b> &Val) { - <b>const char</b> *ArgStart = Arg.c_str(); - <b>char</b> *End; - - <i>// Parse integer part, leaving 'End' pointing to the first non-integer char</i> - Val = (unsigned)strtol(ArgStart, &End, 0); - - <b>while</b> (1) { - <b>switch</b> (*End++) { - <b>case</b> 0: <b>return</b> false; <i>// No error</i> - <b>case</b> 'i': <i>// Ignore the 'i' in KiB if people use that</i> - <b>case</b> 'b': <b>case</b> 'B': <i>// Ignore B suffix</i> - <b>break</b>; - - <b>case</b> 'g': <b>case</b> 'G': Val *= 1024*1024*1024; <b>break</b>; - <b>case</b> 'm': <b>case</b> 'M': Val *= 1024*1024; <b>break</b>; - <b>case</b> 'k': <b>case</b> 'K': Val *= 1024; <b>break</b>; - - default: - <i>// Print an error message if unrecognized character!</i> - <b>return</b> O.error("'" + Arg + "' value invalid for file size argument!"); - } - } -} -</pre></div> - -<p>This function implements a very simple parser for the kinds of strings we are -interested in. Although it has some holes (it allows "<tt>123KKK</tt>" for -example), it is good enough for this example. Note that we use the option -itself to print out the error message (the <tt>error</tt> method always returns -true) in order to get a nice error message (shown below). Now that we have our -parser class, we can use it like this:</p> - -<div class="doc_code"><pre> -<b>static</b> <a href="#cl::opt">cl::opt</a><<b>unsigned</b>, <b>false</b>, FileSizeParser> -MFS(<i>"max-file-size"</i>, <a href="#cl::desc">cl::desc</a>(<i>"Maximum file size to accept"</i>), - <a href="#cl::value_desc">cl::value_desc</a>("<i>size</i>")); -</pre></div> - -<p>Which adds this to the output of our program:</p> - -<div class="doc_code"><pre> -OPTIONS: - -help - display available options (-help-hidden for more) - ... - <b>-max-file-size=<size> - Maximum file size to accept</b> -</pre></div> - -<p>And we can test that our parse works correctly now (the test program just -prints out the max-file-size argument value):</p> - -<div class="doc_code"><pre> -$ ./test -MFS: 0 -$ ./test -max-file-size=123MB -MFS: 128974848 -$ ./test -max-file-size=3G -MFS: 3221225472 -$ ./test -max-file-size=dog --max-file-size option: 'dog' value invalid for file size argument! -</pre></div> - -<p>It looks like it works. The error message that we get is nice and helpful, -and we seem to accept reasonable file sizes. This wraps up the "custom parser" -tutorial.</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="explotingexternal">Exploiting external storage</a> -</h3> - -<div> - <p>Several of the LLVM libraries define static <tt>cl::opt</tt> instances that - will automatically be included in any program that links with that library. - This is a feature. However, sometimes it is necessary to know the value of the - command line option outside of the library. In these cases the library does or - should provide an external storage location that is accessible to users of the - library. Examples of this include the <tt>llvm::DebugFlag</tt> exported by the - <tt>lib/Support/Debug.cpp</tt> file and the <tt>llvm::TimePassesIsEnabled</tt> - flag exported by the <tt>lib/VMCore/PassManager.cpp</tt> file.</p> - -<p>TODO: complete this section</p> - -</div> - -<!-- ======================================================================= --> -<h3> - <a name="dynamicopts">Dynamically adding command line options</a> -</h3> - -<div> - -<p>TODO: fill in this section</p> - -</div> - -</div> - -<!-- *********************************************************************** --> - -<hr> -<address> - <a href="http://jigsaw.w3.org/css-validator/check/referer"><img - src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> - <a href="http://validator.w3.org/check/referer"><img - src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> - - <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> - <a href="http://llvm.org/">LLVM Compiler Infrastructure</a><br> - Last modified: $Date$ -</address> - -</body> -</html> diff --git a/docs/CommandLine.rst b/docs/CommandLine.rst new file mode 100644 index 0000000000..302f5a4cf5 --- /dev/null +++ b/docs/CommandLine.rst @@ -0,0 +1,1615 @@ +.. _commandline: + +============================== +CommandLine 2.0 Library Manual +============================== + +Introduction +============ + +This document describes the CommandLine argument processing library. It will +show you how to use it, and what it can do. The CommandLine library uses a +declarative approach to specifying the command line options that your program +takes. By default, these options declarations implicitly hold the value parsed +for the option declared (of course this `can be changed`_). + +Although there are a **lot** of command line argument parsing libraries out +there in many different languages, none of them fit well with what I needed. By +looking at the features and problems of other libraries, I designed the +CommandLine library to have the following features: + +#. Speed: The CommandLine library is very quick and uses little resources. The + parsing time of the library is directly proportional to the number of + arguments parsed, not the number of options recognized. Additionally, + command line argument values are captured transparently into user defined + global variables, which can be accessed like any other variable (and with the + same performance). + +#. Type Safe: As a user of CommandLine, you don't have to worry about + remembering the type of arguments that you want (is it an int? a string? a + bool? an enum?) and keep casting it around. Not only does this help prevent + error prone constructs, it also leads to dramatically cleaner source code. + +#. No subclasses required: To use CommandLine, you instantiate variables that + correspond to the arguments that you would like to capture, you don't + subclass a parser. This means that you don't have to write **any** + boilerplate code. + +#. Globally accessible: Libraries can specify command line arguments that are + automatically enabled in any tool that links to the library. This is + possible because the application doesn't have to keep a list of arguments to + pass to the parser. This also makes supporting `dynamically loaded options`_ + trivial. + +#. Cleaner: CommandLine supports enum and other types directly, meaning that + there is less error and more security built into the library. You don't have + to worry about whether your integral command line argument accidentally got + assigned a value that is not valid for your enum type. + +#. Powerful: The CommandLine library supports many different types of arguments, + from simple `boolean flags`_ to `scalars arguments`_ (`strings`_, + `integers`_, `enums`_, `doubles`_), to `lists of arguments`_. This is + possible because CommandLine is... + +#. Extensible: It is very simple to add a new argument type to CommandLine. + Simply specify the parser that you want to use with the command line option + when you declare it. `Custom parsers`_ are no problem. + +#. Labor Saving: The CommandLine library cuts down on the amount of grunt work + that you, the user, have to do. For example, it automatically provides a + ``-help`` option that shows the available command line options for your tool. + Additionally, it does most of the basic correctness checking for you. + +#. Capable: The CommandLine library can handle lots of different forms of + options often found in real programs. For example, `positional`_ arguments, + ``ls`` style `grouping`_ options (to allow processing '``ls -lad``' + naturally), ``ld`` style `prefix`_ options (to parse '``-lmalloc + -L/usr/lib``'), and interpreter style options. + +This document will hopefully let you jump in and start using CommandLine in your +utility quickly and painlessly. Additionally it should be a simple reference +manual to figure out how stuff works. If it is failing in some area (or you +want an extension to the library), nag the author, `Chris +Lattner <mailto:sabre@nondot.org>`_. + +Quick Start Guide +================= + +This section of the manual runs through a simple CommandLine'ification of a +basic compiler tool. This is intended to show you how to jump into using the +CommandLine library in your own program, and show you some of the cool things it +can do. + +To start out, you need to include the CommandLine header file into your program: + +.. code-block:: c++ + + #include "llvm/Support/CommandLine.h" + +Additionally, you need to add this as the first line of your main program: + +.. code-block:: c++ + + int main(int argc, char **argv) { + cl::ParseCommandLineOptions(argc, argv); + ... + } + +... which actually parses the arguments and fills in the variable declarations. + +Now that you are ready to support command line arguments, we need to tell the +system which ones we want, and what type of arguments they are. The CommandLine +library uses a declarative syntax to model command line arguments with the +global variable declarations that capture the parsed values. This means that +for every command line option that you would like to support, there should be a +global variable declaration to capture the result. For example, in a compiler, +we would like to support the Unix-standard '``-o <filename>``' option to specify +where to put the output. With the CommandLine library, this is represented like +this: + +.. _scalars arguments: +.. _here: + +.. code-block:: c++ + + cl::opt<string> OutputFilename("o", cl::desc("Specify output filename"), cl::value_desc("filename")); + +This declares a global variable "``OutputFilename``" that is used to capture the +result of the "``o``" argument (first parameter). We specify that this is a +simple scalar option by using the "``cl::opt``" template (as opposed to the +"``cl::list``" template), and tell the CommandLine library that the data +type that we are parsing is a string. + +The second and third parameters (which are optional) are used to specify what to +output for the "``-help``" option. In this case, we get a line that looks like +this: + +:: + + USAGE: compiler [options] + + OPTIONS: + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename + +Because we specified that the command line option should parse using the +``string`` data type, the variable declared is automatically usable as a real +string in all contexts that a normal C++ string object may be used. For +example: + +.. code-block:: c++ + + ... + std::ofstream Output(OutputFilename.c_str()); + if (Output.good()) ... + ... + +There are many different options that you can use to customize the command line +option handling library, but the above example shows the general interface to +these options. The options can be specified in any order, and are specified +with helper functions like `cl::desc(...)`_, so there are no positional +dependencies to remember. The available options are discussed in detail in the +`Reference Guide`_. + +Continuing the example, we would like to have our compiler take an input +filename as well as an output filename, but we do not want the input filename to +be specified with a hyphen (ie, not ``-filename.c``). To support this style of +argument, the CommandLine library allows for `positional`_ arguments to be +specified for the program. These positional arguments are filled with command +line parameters that are not in option form. We use this feature like this: + +.. code-block:: c++ + + + cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::init("-")); + +This declaration indicates that the first positional argument should be treated +as the input filename. Here we use the `cl::init`_ option to specify an initial +value for the command line option, which is used if the option is not specified +(if you do not specify a `cl::init`_ modifier for an option, then the default +constructor for the data type is used to initialize the value). Command line +options default to being optional, so if we would like to require that the user +always specify an input filename, we would add the `cl::Required`_ flag, and we +could eliminate the `cl::init`_ modifier, like this: + +.. code-block:: c++ + + cl::opt<string> InputFilename(cl::Positional, cl::desc("<input file>"), cl::Required); + +Again, the CommandLine library does not require the options to be specified in +any particular order, so the above declaration is equivalent to: + +.. code-block:: c++ + + cl::opt<string> InputFilename(cl::Positional, cl::Required, cl::desc("<input file>")); + +By simply adding the `cl::Required`_ flag, the CommandLine library will +automatically issue an error if the argument is not specified, which shifts all +of the command line option verification code out of your application into the +library. This is just one example of how using flags can alter the default +behaviour of the library, on a per-option basis. By adding one of the +declarations above, the ``-help`` option synopsis is now extended to: + +:: + + USAGE: compiler [options] <input file> + + OPTIONS: + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename + +... indicating that an input filename is expected. + +Boolean Arguments +----------------- + +In addition to input and output filenames, we would like the compiler example to +support three boolean flags: "``-f``" to force writing binary output to a +terminal, "``--quiet``" to enable quiet mode, and "``-q``" for backwards +compatibility with some of our users. We can support these by declaring options +of boolean type like this: + +.. code-block:: c++ + + cl::opt<bool> Force ("f", cl::desc("Enable binary output on terminals")); + cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); + cl::opt<bool> Quiet2("q", cl::desc("Don't print informational messages"), cl::Hidden); + +This does what you would expect: it declares three boolean variables +("``Force``", "``Quiet``", and "``Quiet2``") to recognize these options. Note +that the "``-q``" option is specified with the "`cl::Hidden`_" flag. This +modifier prevents it from being shown by the standard "``-help``" output (note +that it is still shown in the "``-help-hidden``" output). + +The CommandLine library uses a `different parser`_ for different data types. +For example, in the string case, the argument passed to the option is copied +literally into the content of the string variable... we obviously cannot do that +in the boolean case, however, so we must use a smarter parser. In the case of +the boolean parser, it allows no options (in which case it assigns the value of +true to the variable), or it allows the values "``true``" or "``false``" to be +specified, allowing any of the following inputs: + +:: + + compiler -f # No value, 'Force' == true + compiler -f=true # Value specified, 'Force' == true + compiler -f=TRUE # Value specified, 'Force' == true + compiler -f=FALSE # Value specified, 'Force' == false + +... you get the idea. The `bool parser`_ just turns the string values into +boolean values, and rejects things like '``compiler -f=foo``'. Similarly, the +`float`_, `double`_, and `int`_ parsers work like you would expect, using the +'``strtol``' and '``strtod``' C library calls to parse the string value into the +specified data type. + +With the declarations above, "``compiler -help``" emits this: + +:: + + USAGE: compiler [options] <input file> + + OPTIONS: + -f - Enable binary output on terminals + -o - Override output filename + -quiet - Don't print informational messages + -help - display available options (-help-hidden for more) + +and "``compiler -help-hidden``" prints this: + +:: + + USAGE: compiler [options] <input file> + + OPTIONS: + -f - Enable binary output on terminals + -o - Override output filename + -q - Don't print informational messages + -quiet - Don't print informational messages + -help - display available options (-help-hidden for more) + +This brief example has shown you how to use the '`cl::opt`_' class to parse +simple scalar command line arguments. In addition to simple scalar arguments, +the CommandLine library also provides primitives to support CommandLine option +`aliases`_, and `lists`_ of options. + +.. _aliases: + +Argument Aliases +---------------- + +So far, the example works well, except for the fact that we need to check the +quiet condition like this now: + +.. code-block:: c++ + + ... + if (!Quiet && !Quiet2) printInformationalMessage(...); + ... + +... which is a real pain! Instead of defining two values for the same +condition, we can use the "`cl::alias`_" class to make the "``-q``" option an +**alias** for the "``-quiet``" option, instead of providing a value itself: + +.. code-block:: c++ + + cl::opt<bool> Force ("f", cl::desc("Overwrite output files")); + cl::opt<bool> Quiet ("quiet", cl::desc("Don't print informational messages")); + cl::alias QuietA("q", cl::desc("Alias for -quiet"), cl::aliasopt(Quiet)); + +The third line (which is the only one we modified from above) defines a "``-q``" +alias that updates the "``Quiet``" variable (as specified by the `cl::aliasopt`_ +modifier) whenever it is specified. Because aliases do not hold state, the only +thing the program has to query is the ``Quiet`` variable now. Another nice +feature of aliases is that they automatically hide themselves from the ``-help`` +output (although, again, they are still visible in the ``-help-hidden output``). + +Now the application code can simply use: + +.. code-block:: c++ + + ... + if (!Quiet) printInformationalMessage(...); + ... + +... which is much nicer! The "`cl::alias`_" can be used to specify an +alternative name for any variable type, and has many uses. + +.. _unnamed alternatives using the generic parser: + +Selecting an alternative from a set of possibilities +---------------------------------------------------- + +So far we have seen how the CommandLine library handles builtin types like +``std::string``, ``bool`` and ``int``, but how does it handle things it doesn't +know about, like enums or '``int*``'s? + +The answer is that it uses a table-driven generic parser (unless you specify +your own parser, as described in the `Extension Guide`_). This parser maps +literal strings to whatever type is required, and requires you to tell it what +this mapping should be. + +Let's say that we would like to add four optimization levels to our optimizer, +using the standard flags "``-g``", "``-O0``", "``-O1``", and "``-O2``". We +could easily implement this with boolean options like above, but there are +several problems with this strategy: + +#. A user could specify more than one of the options at a time, for example, + "``compiler -O3 -O2``". The CommandLine library would not be able to catch + this erroneous input for us. + +#. We would have to test 4 different variables to see which ones are set. + +#. This doesn't map to the numeric levels that we want... so we cannot easily + see if some level >= "``-O1``" is enabled. + +To cope with these problems, we can use an enum value, and have the CommandLine +library fill it in with the appropriate level directly, which is used like this: + +.. code-block:: c++ + + enum OptLevel { + g, O1, O2, O3 + }; + + cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"), + cl::values( + clEnumVal(g , "No optimizations, enable debugging"), + clEnumVal(O1, "Enable trivial optimizations"), + clEnumVal(O2, "Enable default optimizations"), + clEnumVal(O3, "Enable expensive optimizations"), + clEnumValEnd)); + + ... + if (OptimizationLevel >= O2) doPartialRedundancyElimination(...); + ... + +This declaration defines a variable "``OptimizationLevel``" of the +"``OptLevel``" enum type. This variable can be assigned any of the values that +are listed in the declaration (Note that the declaration list must be terminated +with the "``clEnumValEnd``" argument!). The CommandLine library enforces that +the user can only specify one of the options, and it ensure that only valid enum +values can be specified. The "``clEnumVal``" macros ensure that the command +line arguments matched the enum values. With this option added, our help output +now is: + +:: + + USAGE: compiler [options] <input file> + + OPTIONS: + Choose optimization level: + -g - No optimizations, enable debugging + -O1 - Enable trivial optimizations + -O2 - Enable default optimizations + -O3 - Enable expensive optimizations + -f - Enable binary output on terminals + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename + -quiet - Don't print informational messages + +In this case, it is sort of awkward that flag names correspond directly to enum +names, because we probably don't want a enum definition named "``g``" in our +program. Because of this, we can alternatively write this example like this: + +.. code-block:: c++ + + enum OptLevel { + Debug, O1, O2, O3 + }; + + cl::opt<OptLevel> OptimizationLevel(cl::desc("Choose optimization level:"), + cl::values( + clEnumValN(Debug, "g", "No optimizations, enable debugging"), + clEnumVal(O1 , "Enable trivial optimizations"), + clEnumVal(O2 , "Enable default optimizations"), + clEnumVal(O3 , "Enable expensive optimizations"), + clEnumValEnd)); + + ... + if (OptimizationLevel == Debug) outputDebugInfo(...); + ... + +By using the "``clEnumValN``" macro instead of "``clEnumVal``", we can directly +specify the name that the flag should get. In general a direct mapping is nice, +but sometimes you can't or don't want to preserve the mapping, which is when you +would use it. + +Named Alternatives +------------------ + +Another useful argument form is a named alternative style. We shall use this +style in our compiler to specify different debug levels that can be used. +Instead of each debug level being its own switch, we want to support the +following options, of which only one can be specified at a time: +"``--debug-level=none``", "``--debug-level=quick``", +"``--debug-level=detailed``". To do this, we use the exact same format as our +optimization level flags, but we also specify an option name. For this case, +the code looks like this: + +.. code-block:: c++ + + enum DebugLev { + nodebuginfo, quick, detailed + }; + + // Enable Debug Options to be specified on the command line + cl::opt<DebugLev> DebugLevel("debug_level", cl::desc("Set the debugging level:"), + cl::values( + clEnumValN(nodebuginfo, "none", "disable debug information"), + clEnumVal(quick, "enable quick debug information"), + clEnumVal(detailed, "enable detailed debug information"), + clEnumValEnd)); + +This definition defines an enumerated command line variable of type "``enum +DebugLev``", which works exactly the same way as before. The difference here is +just the interface exposed to the user of your program and the help output by +the "``-help``" option: + +:: + + USAGE: compiler [options] <input file> + + OPTIONS: + Choose optimization level: + -g - No optimizations, enable debugging + -O1 - Enable trivial optimizations + -O2 - Enable default optimizations + -O3 - Enable expensive optimizations + -debug_level - Set the debugging level: + =none - disable debug information + =quick - enable quick debug information + =detailed - enable detailed debug information + -f - Enable binary output on terminals + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename + -quiet - Don't print informational messages + +Again, the only structural difference between the debug level declaration and +the optimization level declaration is that the debug level declaration includes +an option name (``"debug_level"``), which automatically changes how the library +processes the argument. The CommandLine library supports both forms so that you +can choose the form most appropriate for your application. + +.. _lists: + +Parsing a list of options +------------------------- + +Now that we have the standard run-of-the-mill argument types out of the way, +lets get a little wild and crazy. Lets say that we want our optimizer to accept +a **list** of optimizations to perform, allowing duplicates. For example, we +might want to run: "``compiler -dce -constprop -inline -dce -strip``". In this +case, the order of the arguments and the number of appearances is very +important. This is what the "``cl::list``" template is for. First, start by +defining an enum of the optimizations that you would like to perform: + +.. code-block:: c++ + + enum Opts { + // 'inline' is a C++ keyword, so name it 'inlining' + dce, constprop, inlining, strip + }; + +Then define your "``cl::list``" variable: + +.. code-block:: c++ + + cl::list<Opts> OptimizationList(cl::desc("Available Optimizations:"), + cl::values( + clEnumVal(dce , "Dead Code Elimination"), + clEnumVal(constprop , "Constant Propagation"), + clEnumValN(inlining, "inline", "Procedure Integration"), + clEnumVal(strip , "Strip Symbols"), + clEnumValEnd)); + +This defines a variable that is conceptually of the type +"``std::vector<enum Opts>``". Thus, you can access it with standard vector +methods: + +.. code-block:: c++ + + for (unsigned i = 0; i != OptimizationList.size(); ++i) + switch (OptimizationList[i]) + ... + +... to iterate through the list of options specified. + +Note that the "``cl::list``" template is completely general and may be used with +any data types or other arguments that you can use with the "``cl::opt``" +template. One especially useful way to use a list is to capture all of the +positional arguments together if there may be more than one specified. In the +case of a linker, for example, the linker takes several '``.o``' files, and +needs to capture them into a list. This is naturally specified as: + +.. code-block:: c++ + + ... + cl::list<std::string> InputFilenames(cl::Positional, cl::desc("<Input files>"), cl::OneOrMore); + ... + +This variable works just like a "``vector<string>``" object. As such, accessing +the list is simple, just like above. In this example, we used the +`cl::OneOrMore`_ modifier to inform the CommandLine library that it is an error +if the user does not specify any ``.o`` files on our command line. Again, this +just reduces the amount of checking we have to do. + +Collecting options as a set of flags +------------------------------------ + +Instead of collecting sets of options in a list, it is also possible to gather +information for enum values in a **bit vector**. The representation used by the +`cl::bits`_ class is an ``unsigned`` integer. An enum value is represented by a +0/1 in the enum's ordinal value bit position. 1 indicating that the enum was +specified, 0 otherwise. As each specified value is parsed, the resulting enum's +bit is set in the option's bit vector: + +.. code-block:: c++ + + bits |= 1 << (unsigned)enum; + +Options that are specified multiple times are redundant. Any instances after +the first are discarded. + +Reworking the above list example, we could replace `cl::list`_ with `cl::bits`_: + +.. code-block:: c++ + + cl::bits<Opts> OptimizationBits(cl::desc("Available Optimizations:"), + cl::values( + clEnumVal(dce , "Dead Code Elimination"), + clEnumVal(constprop , "Constant Propagation"), + clEnumValN(inlining, "inline", "Procedure Integration"), + clEnumVal(strip , "Strip Symbols"), + clEnumValEnd)); + +To test to see if ``constprop`` was specified, we can use the ``cl:bits::isSet`` +function: + +.. code-block:: c++ + + if (OptimizationBits.isSet(constprop)) { + ... + } + +It's also possible to get the raw bit vector using the ``cl::bits::getBits`` +function: + +.. code-block:: c++ + + unsigned bits = OptimizationBits.getBits(); + +Finally, if external storage is used, then the location specified must be of +**type** ``unsigned``. In all other ways a `cl::bits`_ option is equivalent to a +`cl::list`_ option. + +.. _additional extra text: + +Adding freeform text to help output +----------------------------------- + +As our program grows and becomes more mature, we may decide to put summary +information about what it does into the help output. The help output is styled +to look similar to a Unix ``man`` page, providing concise information about a +program. Unix ``man`` pages, however often have a description about what the +program does. To add this to your CommandLine program, simply pass a third +argument to the `cl::ParseCommandLineOptions`_ call in main. This additional +argument is then printed as the overview information for your program, allowing +you to include any additional information that you want. For example: + +.. code-block:: c++ + + int main(int argc, char **argv) { + cl::ParseCommandLineOptions(argc, argv, " CommandLine compiler example\n\n" + " This program blah blah blah...\n"); + ... + } + +would yield the help output: + +:: + + **OVERVIEW: CommandLine compiler example + + This program blah blah blah...** + + USAGE: compiler [options] <input file> + + OPTIONS: + ... + -help - display available options (-help-hidden for more) + -o <filename> - Specify output filename + +.. _Reference Guide: + +Reference Guide +=============== + +Now that you know the basics of how to use the CommandLine library, this section +will give you the detailed information you need to tune how command line options +work, as well as information on more "advanced" command line option processing +capabilities. + +.. _positional: +.. _positional argument: +.. _Positional Arguments: +.. _Positional arguments section: +.. _positional options: + +Positional Arguments +-------------------- + +Positional arguments are those arguments that are not named, and are not +specified with a hyphen. Positional arguments should be used when an option is +specified by its position alone. For example, the standard Unix ``grep`` tool +takes a regular expression argument, and an optional filename to search through +(which defaults to standard input if a filename is not specified). Using the +CommandLine library, this would be specified as: + +.. code-block:: c++ + + cl::opt<string> Regex (cl::Positional, cl::desc("<regular expression>"), cl::Required); + cl::opt<string> Filename(cl::Positional, cl::desc("<input file>"), cl::init("-")); + +Given these two option declarations, the ``-help`` output for our grep +replacement would look like this: + +:: + + USAGE: spiffygrep [options] <regular expression> <input file> + + OPTIONS: + -help - display available options (-help-hidden for more) + +... and the resultant program could be used just like the standard ``grep`` +tool. + +Positional arguments are sorted by their order of construction. This means that +command line options will be ordered according to how they are listed in a .cpp +file, but will not have an ordering defined if the positional arguments are +defined in multiple .cpp files. The fix for this problem is simply to define +all of your positional arguments in one .cpp file. + +Specifying positional options with hyphens +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Sometimes you may want to specify a value to your positional argument that +starts with a hyphen (for example, searching for '``-foo``' in a file). At +first, you will have trouble doing this, because it will try to find an argument +named '``-foo``', and will fail (and single quotes will not save you). Note +that the system ``grep`` has the same problem: + +:: + + $ spiffygrep '-foo' test.txt + Unknown command line argument '-foo'. Try: spiffygrep -help' + + $ grep '-foo' test.txt + grep: illegal option -- f + grep: illegal option -- o + grep: illegal option -- o + Usage: grep -hblcnsviw pattern file . . . + +The solution for this problem is the same for both your tool and the system +version: use the '``--``' marker. When the user specifies '``--``' on the +command line, it is telling the program that all options after the '``--``' +should be treated as positional arguments, not options. Thus, we can use it +like this: + +:: + + $ spiffygrep -- -foo test.txt + ...output... + +Determining absolute position with getPosition() +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Sometimes an option can affect or modify the meaning of another option. For +example, consider ``gcc``'s ``-x LANG`` option. This tells ``gcc`` to ignore the +suffix of subsequent positional arguments and force the file to be interpreted +as if it contained source code in language ``LANG``. In order to handle this +properly, you need to know the absolute position of each argument, especially +those in lists, so their interaction(s) can be applied correctly. This is also +useful for options like ``-llibname`` which is actually a positional argument +that starts with a dash. + +So, generally, the problem is that you have two ``cl::list`` variables that +interact in some way. To ensure the correct interaction, you can use the +``cl::list::getPosition(optnum)`` method. This method returns the absolute +position (as found on the command line) of the ``optnum`` item in the +``cl::list``. + +The idiom for usage is like this: + +.. code-block:: c++ + + static cl::list<std::string> Files(cl::Positional, cl::OneOrMore); + static cl::list<std::string> Libraries("l", cl::ZeroOrMore); + + int main(int argc, char**argv) { + // ... + std::vector<std::string>::iterator fileIt = Files.begin(); + std::vector<std::string>::iterator libIt = Libraries.begin(); + unsigned libPos = 0, filePos = 0; + while ( 1 ) { + if ( libIt != Libraries.end() ) + libPos = Libraries.getPosition( libIt - Libraries.begin() ); + else + libPos = 0; + if ( fileIt != Files.end() ) + filePos = Files.getPosition( fileIt - Files.begin() ); + else + filePos = 0; + + if ( filePos != 0 && (libPos == 0 || filePos < libPos) ) { + // Source File Is next + ++fileIt; + } + else if ( libPos != 0 && (filePos == 0 || libPos < filePos) ) { + // Library is next + ++libIt; + } + else + break; // we're done with the list + } + } + +Note that, for compatibility reasons, the ``cl::opt`` also supports an +``unsigned getPosition()`` option that will provide the absolute position of +that option. You can apply the same approach as above with a ``cl::opt`` and a +``cl::list`` option as you can with two lists. + +.. _interpreter style options: +.. _cl::ConsumeAfter: +.. _this section for more information: + +The ``cl::ConsumeAfter`` modifier +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::ConsumeAfter`` `formatting option`_ is used to construct programs that +use "interpreter style" option processing. With this style of option +processing, all arguments specified after the last positional argument are +treated as special interpreter arguments that are not interpreted by the command +line argument. + +As a concrete example, lets say we are developing a replacement for the standard +Unix Bourne shell (``/bin/sh``). To run ``/bin/sh``, first you specify options +to the shell itself (like ``-x`` which turns on trace output), then you specify +the name of the script to run, then you specify arguments to the script. These +arguments to the script are parsed by the Bourne shell command line option +processor, but are not interpreted as options to the shell itself. Using the +CommandLine library, we would specify this as: + +.. code-block:: c++ + + cl::opt<string> Script(cl::Positional, cl::desc("<input script>"), cl::init("-")); + cl::list<string> Argv(cl::ConsumeAfter, cl::desc("<program arguments>...")); + cl::opt<bool> Trace("x", cl::desc("Enable trace output")); + +which automatically provides the help output: + +:: + + USAGE: spiffysh [options] <input script> <program arguments>... + + OPTIONS: + -help - display available options (-help-hidden for more) + -x - Enable trace output + +At runtime, if we run our new shell replacement as ```spiffysh -x test.sh -a -x +-y bar``', the ``Trace`` variable will be set to true, the ``Script`` variable +will be set to "``test.sh``", and the ``Argv`` list will contain ``["-a", "-x", +"-y", "bar"]``, because they were specified after the last positional argument +(which is the script name). + +There are several limitations to when ``cl::ConsumeAfter`` options can be +specified. For example, only one ``cl::ConsumeAfter`` can be specified per +program, there must be at least one `positional argument`_ specified, there must +not be any `cl::list`_ positional arguments, and the ``cl::ConsumeAfter`` option +should be a `cl::list`_ option. + +.. _can be changed: +.. _Internal vs External Storage: + +Internal vs External Storage +---------------------------- + +By default, all command line options automatically hold the value that they +parse from the command line. This is very convenient in the common case, +especially when combined with the ability to define command line options in the +files that use them. This is called the internal storage model. + +Sometimes, however, it is nice to separate the command line option processing +code from the storage of the value parsed. For example, lets say that we have a +'``-debug``' option that we would like to use to enable debug information across +the entire body of our program. In this case, the boolean value controlling the +debug code should be globally accessible (in a header file, for example) yet the +command line option processing code should not be exposed to all of these +clients (requiring lots of .cpp files to ``#include CommandLine.h``). + +To do this, set up your .h file with your option, like this for example: + +.. code-block:: c++ + + // DebugFlag.h - Get access to the '-debug' command line option + // + + // DebugFlag - This boolean is set to true if the '-debug' command line option + // is specified. This should probably not be referenced directly, instead, use + // the DEBUG macro below. + // + extern bool DebugFlag; + + // DEBUG macro - This macro should be used by code to emit debug information. + // In the '-debug' option is specified on the command line, and if this is a + // debug build, then the code specified as the option to the macro will be + // executed. Otherwise it will not be. + #ifdef NDEBUG + #define DEBUG(X) + #else + #define DEBUG(X) do { if (DebugFlag) { X; } } while (0) + #endif + +This allows clients to blissfully use the ``DEBUG()`` macro, or the +``DebugFlag`` explicitly if they want to. Now we just need to be able to set +the ``DebugFlag`` boolean when the option is set. To do this, we pass an +additional argument to our command line argument processor, and we specify where +to fill in with the `cl::location`_ attribute: + +.. code-block:: c++ + + bool DebugFlag; // the actual value + static cl::opt<bool, true> // The parser + Debug("debug", cl::desc("Enable debug output"), cl::Hidden, cl::location(DebugFlag)); + +In the above example, we specify "``true``" as the second argument to the +`cl::opt`_ template, indicating that the template should not maintain a copy of +the value itself. In addition to this, we specify the `cl::location`_ +attribute, so that ``DebugFlag`` is automatically set. + +Option Attributes +----------------- + +This section describes the basic attributes that you can specify on options. + +* The option name attribute (which is required for all options, except + `positional options`_) specifies what the option name is. This option is + specified in simple double quotes: + + .. code-block:: c++ + + cl::opt<**bool**> Quiet("quiet"); + +.. _cl::desc(...): + +* The **cl::desc** attribute specifies a description for the option to be + shown in the ``-help`` output for the program. + +.. _cl::value_desc: + +* The **cl::value_desc** attribute specifies a string that can be used to + fine tune the ``-help`` output for a command line option. Look `here`_ for an + example. + +.. _cl::init: + +* The **cl::init** attribute specifies an initial value for a `scalar`_ + option. If this attribute is not specified then the command line option value + defaults to the value created by the default constructor for the + type. + + .. warning:: + + If you specify both **cl::init** and **cl::location** for an option, you + must specify **cl::location** first, so that when the command-line parser + sees **cl::init**, it knows where to put the initial value. (You will get an + error at runtime if you don't put them in the right order.) + +.. _cl::location: + +* The **cl::location** attribute where to store the value for a parsed command + line option if using external storage. See the section on `Internal vs + External Storage`_ for more information. + +.. _cl::aliasopt: + +* The **cl::aliasopt** attribute specifies which option a `cl::alias`_ option is + an alias for. + +.. _cl::values: + +* The **cl::values** attribute specifies the string-to-value mapping to be used + by the generic parser. It takes a **clEnumValEnd terminated** list of + (option, value, description) triplets that specify the option name, the value + mapped to, and the description shown in the ``-help`` for the tool. Because + the generic parser is used most frequently with enum values, two macros are + often useful: + + #. The **clEnumVal** macro is used as a nice simple way to specify a triplet + for an enum. This macro automatically makes the option name be the same as + the enum name. The first option to the macro is the enum, the second is + the description for the command line option. + + #. The **clEnumValN** macro is used to specify macro options where the option + name doesn't equal the enum name. For this macro, the first argument is + the enum value, the second is the flag name, and the second is the + description. + + You will get a compile time error if you try to use cl::values with a parser + that does not support it. + +.. _cl::multi_val: + +* The **cl::multi_val** attribute specifies that this option takes has multiple + values (example: ``-sectalign segname sectname sectvalue``). This attribute + takes one unsigned argument - the number of values for the option. This + attribute is valid only on ``cl::list`` options (and will fail with compile + error if you try to use it with other option types). It is allowed to use all + of the usual modifiers on multi-valued options (besides + ``cl::ValueDisallowed``, obviously). + +Option Modifiers +---------------- + +Option modifiers are the flags and expressions that you pass into the +constructors for `cl::opt`_ and `cl::list`_. These modifiers give you the +ability to tweak how options are parsed and how ``-help`` output is generated to +fit your application well. + +These options fall into five main categories: + +#. Hiding an option from ``-help`` output + +#. Controlling the number of occurrences required and allowed + +#. Controlling whether or not a value must be specified + +#. Controlling other formatting options + +#. Miscellaneous option modifiers + +It is not possible to specify two options from the same category (you'll get a +runtime error) to a single option, except for options in the miscellaneous +category. The CommandLine library specifies defaults for all of these settings +that are the most useful in practice and the most common, which mean that you +usually shouldn't have to worry about these. + +Hiding an option from ``-help`` output +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::NotHidden``, ``cl::Hidden``, and ``cl::ReallyHidden`` modifiers are +used to control whether or not an option appears in the ``-help`` and +``-help-hidden`` output for the compiled program: + +.. _cl::NotHidden: + +* The **cl::NotHidden** modifier (which is the default for `cl::opt`_ and + `cl::list`_ options) indicates the option is to appear in both help + listings. + +.. _cl::Hidden: + +* The **cl::Hidden** modifier (which is the default for `cl::alias`_ options) + indicates that the option should not appear in the ``-help`` output, but + should appear in the ``-help-hidden`` output. + +.. _cl::ReallyHidden: + +* The **cl::ReallyHidden** modifier indicates that the option should not appear + in any help output. + +Controlling the number of occurrences required and allowed +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +This group of options is used to control how many time an option is allowed (or +required) to be specified on the command line of your program. Specifying a +value for this setting allows the CommandLine library to do error checking for +you. + +The allowed values for this option group are: + +.. _cl::Optional: + +* The **cl::Optional** modifier (which is the default for the `cl::opt`_ and + `cl::alias`_ classes) indicates that your program will allow either zero or + one occurrence of the option to be specified. + +.. _cl::ZeroOrMore: + +* The **cl::ZeroOrMore** modifier (which is the default for the `cl::list`_ + class) indicates that your program will allow the option to be specified zero + or more times. + +.. _cl::Required: + +* The **cl::Required** modifier indicates that the specified option must be + specified exactly one time. + +.. _cl::OneOrMore: + +* The **cl::OneOrMore** modifier indicates that the option must be specified at + least one time. + +* The **cl::ConsumeAfter** modifier is described in the `Positional arguments + section`_. + +If an option is not specified, then the value of the option is equal to the +value specified by the `cl::init`_ attribute. If the ``cl::init`` attribute is +not specified, the option value is initialized with the default constructor for +the data type. + +If an option is specified multiple times for an option of the `cl::opt`_ class, +only the last value will be retained. + +Controlling whether or not a value must be specified +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +This group of options is used to control whether or not the option allows a +value to be present. In the case of the CommandLine library, a value is either +specified with an equal sign (e.g. '``-index-depth=17``') or as a trailing +string (e.g. '``-o a.out``'). + +The allowed values for this option group are: + +.. _cl::ValueOptional: + +* The **cl::ValueOptional** modifier (which is the default for ``bool`` typed + options) specifies that it is acceptable to have a value, or not. A boolean + argument can be enabled just by appearing on the command line, or it can have + an explicit '``-foo=true``'. If an option is specified with this mode, it is + illegal for the value to be provided without the equal sign. Therefore + '``-foo true``' is illegal. To get this behavior, you must use + the `cl::ValueRequired`_ modifier. + +.. _cl::ValueRequired: + +* The **cl::ValueRequired** modifier (which is the default for all other types + except for `unnamed alternatives using the generic parser`_) specifies that a + value must be provided. This mode informs the command line library that if an + option is not provides with an equal sign, that the next argument provided + must be the value. This allows things like '``-o a.out``' to work. + +.. _cl::ValueDisallowed: + +* The **cl::ValueDisallowed** modifier (which is the default for `unnamed + alternatives using the generic parser`_) indicates that it is a runtime error + for the user to specify a value. This can be provided to disallow users from + providing options to boolean options (like '``-foo=true``'). + +In general, the default values for this option group work just like you would +want them to. As mentioned above, you can specify the `cl::ValueDisallowed`_ +modifier to a boolean argument to restrict your command line parser. These +options are mostly useful when `extending the library`_. + +.. _formatting option: + +Controlling other formatting options +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The formatting option group is used to specify that the command line option has +special abilities and is otherwise different from other command line arguments. +As usual, you can only specify one of these arguments at most. + +.. _cl::NormalFormatting: + +* The **cl::NormalFormatting** modifier (which is the default all options) + specifies that this option is "normal". + +.. _cl::Positional: + +* The **cl::Positional** modifier specifies that this is a positional argument + that does not have a command line option associated with it. See the + `Positional Arguments`_ section for more information. + +* The **cl::ConsumeAfter** modifier specifies that this option is used to + capture "interpreter style" arguments. See `this section for more + information`_. + +.. _prefix: +.. _cl::Prefix: + +* The **cl::Prefix** modifier specifies that this option prefixes its value. + With 'Prefix' options, the equal sign does not separate the value from the + option name specified. Instead, the value is everything after the prefix, + including any equal sign if present. This is useful for processing odd + arguments like ``-lmalloc`` and ``-L/usr/lib`` in a linker tool or + ``-DNAME=value`` in a compiler tool. Here, the '``l``', '``D``' and '``L``' + options are normal string (or list) options, that have the **cl::Prefix** + modifier added to allow the CommandLine library to recognize them. Note that + **cl::Prefix** options must not have the **cl::ValueDisallowed** modifier + specified. + +.. _grouping: +.. _cl::Grouping: + +* The **cl::Grouping** modifier is used to implement Unix-style tools (like + ``ls``) that have lots of single letter arguments, but only require a single + dash. For example, the '``ls -labF``' command actually enables four different + options, all of which are single letters. Note that **cl::Grouping** options + cannot have values. + +The CommandLine library does not restrict how you use the **cl::Prefix** or +**cl::Grouping** modifiers, but it is possible to specify ambiguous argument +settings. Thus, it is possible to have multiple letter options that are prefix +or grouping options, and they will still work as designed. + +To do this, the CommandLine library uses a greedy algorithm to parse the input +option into (potentially multiple) prefix and grouping options. The strategy +basically looks like this: + +:: + + parse(string OrigInput) { + + 1. string input = OrigInput; + 2. if (isOption(input)) return getOption(input).parse(); // Normal option + 3. while (!isOption(input) && !input.empty()) input.pop_back(); // Remove the last letter + 4. if (input.empty()) return error(); // No matching option + 5. if (getOption(input).isPrefix()) + return getOption(input).parse(input); + 6. while (!input.empty()) { // Must be grouping options + getOption(input).parse(); + OrigInput.erase(OrigInput.begin(), OrigInput.begin()+input.length()); + input = OrigInput; + while (!isOption(input) && !input.empty()) input.pop_back(); + } + 7. if (!OrigInput.empty()) error(); + + } + +Miscellaneous option modifiers +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The miscellaneous option modifiers are the only flags where you can specify more +than one flag from the set: they are not mutually exclusive. These flags +specify boolean properties that modify the option. + +.. _cl::CommaSeparated: + +* The **cl::CommaSeparated** modifier indicates that any commas specified for an + option's value should be used to split the value up into multiple values for + the option. For example, these two options are equivalent when + ``cl::CommaSeparated`` is specified: "``-foo=a -foo=b -foo=c``" and + "``-foo=a,b,c``". This option only makes sense to be used in a case where the + option is allowed to accept one or more values (i.e. it is a `cl::list`_ + option). + +.. _cl::PositionalEatsArgs: + +* The **cl::PositionalEatsArgs** modifier (which only applies to positional + arguments, and only makes sense for lists) indicates that positional argument + should consume any strings after it (including strings that start with a "-") + up until another recognized positional argument. For example, if you have two + "eating" positional arguments, "``pos1``" and "``pos2``", the string "``-pos1 + -foo -bar baz -pos2 -bork``" would cause the "``-foo -bar -baz``" strings to + be applied to the "``-pos1``" option and the "``-bork``" string to be applied + to the "``-pos2``" option. + +.. _cl::Sink: + +* The **cl::Sink** modifier is used to handle unknown options. If there is at + least one option with ``cl::Sink`` modifier specified, the parser passes + unrecognized option strings to it as values instead of signaling an error. As + with ``cl::CommaSeparated``, this modifier only makes sense with a `cl::list`_ + option. + +So far, these are the only three miscellaneous option modifiers. + +.. _response files: + +Response files +^^^^^^^^^^^^^^ + +Some systems, such as certain variants of Microsoft Windows and some older +Unices have a relatively low limit on command-line length. It is therefore +customary to use the so-called 'response files' to circumvent this +restriction. These files are mentioned on the command-line (using the "@file") +syntax. The program reads these files and inserts the contents into argv, +thereby working around the command-line length limits. Response files are +enabled by an optional fourth argument to `cl::ParseEnvironmentOptions`_ and +`cl::ParseCommandLineOptions`_. + +Top-Level Classes and Functions +------------------------------- + +Despite all of the built-in flexibility, the CommandLine option library really +only consists of one function `cl::ParseCommandLineOptions`_) and three main +classes: `cl::opt`_, `cl::list`_, and `cl::alias`_. This section describes +these three classes in detail. + +.. _cl::ParseCommandLineOptions: + +The ``cl::ParseCommandLineOptions`` function +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::ParseCommandLineOptions`` function is designed to be called directly +from ``main``, and is used to fill in the values of all of the command line +option variables once ``argc`` and ``argv`` are available. + +The ``cl::ParseCommandLineOptions`` function requires two parameters (``argc`` +and ``argv``), but may also take an optional third parameter which holds +`additional extra text`_ to emit when the ``-help`` option is invoked, and a +fourth boolean parameter that enables `response files`_. + +.. _cl::ParseEnvironmentOptions: + +The ``cl::ParseEnvironmentOptions`` function +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::ParseEnvironmentOptions`` function has mostly the same effects as +`cl::ParseCommandLineOptions`_, except that it is designed to take values for +options from an environment variable, for those cases in which reading the +command line is not convenient or desired. It fills in the values of all the +command line option variables just like `cl::ParseCommandLineOptions`_ does. + +It takes four parameters: the name of the program (since ``argv`` may not be +available, it can't just look in ``argv[0]``), the name of the environment +variable to examine, the optional `additional extra text`_ to emit when the +``-help`` option is invoked, and the boolean switch that controls whether +`response files`_ should be read. + +``cl::ParseEnvironmentOptions`` will break the environment variable's value up +into words and then process them using `cl::ParseCommandLineOptions`_. +**Note:** Currently ``cl::ParseEnvironmentOptions`` does not support quoting, so +an environment variable containing ``-option "foo bar"`` will be parsed as three +words, ``-option``, ``"foo``, and ``bar"``, which is different from what you +would get from the shell with the same input. + +The ``cl::SetVersionPrinter`` function +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::SetVersionPrinter`` function is designed to be called directly from +``main`` and *before* ``cl::ParseCommandLineOptions``. Its use is optional. It +simply arranges for a function to be called in response to the ``--version`` +option instead of having the ``CommandLine`` library print out the usual version +string for LLVM. This is useful for programs that are not part of LLVM but wish +to use the ``CommandLine`` facilities. Such programs should just define a small +function that takes no arguments and returns ``void`` and that prints out +whatever version information is appropriate for the program. Pass the address of +that function to ``cl::SetVersionPrinter`` to arrange for it to be called when +the ``--version`` option is given by the user. + +.. _cl::opt: +.. _scalar: + +The ``cl::opt`` class +^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::opt`` class is the class used to represent scalar command line +options, and is the one used most of the time. It is a templated class which +can take up to three arguments (all except for the first have default values +though): + +.. code-block:: c++ + + namespace cl { + template <class DataType, bool ExternalStorage = false, + class ParserClass = parser<DataType> > + class opt; + } + +The first template argument specifies what underlying data type the command line +argument is, and is used to select a default parser implementation. The second +template argument is used to specify whether the option should contain the +storage for the option (the default) or whether external storage should be used +to contain the value parsed for the option (see `Internal vs External Storage`_ +for more information). + +The third template argument specifies which parser to use. The default value +selects an instantiation of the ``parser`` class based on the underlying data +type of the option. In general, this default works well for most applications, +so this option is only used when using a `custom parser`_. + +.. _lists of arguments: +.. _cl::list: + +The ``cl::list`` class +^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::list`` class is the class used to represent a list of command line +options. It too is a templated class which can take up to three arguments: + +.. code-block:: c++ + + namespace cl { + template <class DataType, class Storage = bool, + class ParserClass = parser<DataType> > + class list; + } + +This class works the exact same as the `cl::opt`_ class, except that the second +argument is the **type** of the external storage, not a boolean value. For this +class, the marker type '``bool``' is used to indicate that internal storage +should be used. + +.. _cl::bits: + +The ``cl::bits`` class +^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::bits`` class is the class used to represent a list of command line +options in the form of a bit vector. It is also a templated class which can +take up to three arguments: + +.. code-block:: c++ + + namespace cl { + template <class DataType, class Storage = bool, + class ParserClass = parser<DataType> > + class bits; + } + +This class works the exact same as the `cl::list`_ class, except that the second +argument must be of **type** ``unsigned`` if external storage is used. + +.. _cl::alias: + +The ``cl::alias`` class +^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::alias`` class is a nontemplated class that is used to form aliases for +other arguments. + +.. code-block:: c++ + + namespace cl { + class alias; + } + +The `cl::aliasopt`_ attribute should be used to specify which option this is an +alias for. Alias arguments default to being `cl::Hidden`_, and use the aliased +options parser to do the conversion from string to data. + +.. _cl::extrahelp: + +The ``cl::extrahelp`` class +^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +The ``cl::extrahelp`` class is a nontemplated class that allows extra help text +to be printed out for the ``-help`` option. + +.. code-block:: c++ + + namespace cl { + struct extrahelp; + } + +To use the extrahelp, simply construct one with a ``const char*`` parameter to +the constructor. The text passed to the constructor will be printed at the +bottom of the help message, verbatim. Note that multiple ``cl::extrahelp`` +**can** be used, but this practice is discouraged. If your tool needs to print +additional help information, put all that help into a single ``cl::extrahelp`` +instance. + +For example: + +.. code-block:: c++ + + cl::extrahelp("\nADDITIONAL HELP:\n\n This is the extra help\n"); + +.. _different parser: +.. _discussed previously: + +Builtin parsers +--------------- + +Parsers control how the string value taken from the command line is translated +into a typed value, suitable for use in a C++ program. By default, the +CommandLine library uses an instance of ``parser<type>`` if the command line +option specifies that it uses values of type '``type``'. Because of this, +custom option processing is specified with specializations of the '``parser``' +class. + +The CommandLine library provides the following builtin parser specializations, +which are sufficient for most applications. It can, however, also be extended to +work with new data types and new ways of interpreting the same data. See the +`Writing a Custom Parser`_ for more details on this type of library extension. + +.. _enums: +.. _cl::parser: + +* The generic ``parser<t>`` parser can be used to map strings values to any data + type, through the use of the `cl::values`_ property, which specifies the + mapping information. The most common use of this parser is for parsing enum + values, which allows you to use the CommandLine library for all of the error + checking to make sure that only valid enum values are specified (as opposed to + accepting arbitrary strings). Despite this, however, the generic parser class + can be used for any data type. + +.. _boolean flags: +.. _bool parser: + +* The **parser<bool> specialization** is used to convert boolean strings to a + boolean value. Currently accepted strings are "``true``", "``TRUE``", + "``True``", "``1``", "``false``", "``FALSE``", "``False``", and "``0``". + +* The **parser<boolOrDefault> specialization** is used for cases where the value + is boolean, but we also need to know whether the option was specified at all. + boolOrDefault is an enum with 3 values, BOU_UNSET, BOU_TRUE and BOU_FALSE. + This parser accepts the same strings as **``parser<bool>``**. + +.. _strings: + +* The **parser<string> specialization** simply stores the parsed string into the + string value specified. No conversion or modification of the data is + performed. + +.. _integers: +.. _int: + +* The **parser<int> specialization** uses the C ``strtol`` function to parse the + string input. As such, it will accept a decimal number (with an optional '+' + or '-' prefix) which must start with a non-zero digit. It accepts octal + numbers, which are identified with a '``0``' prefix digit, and hexadecimal + numbers with a prefix of '``0x``' or '``0X``'. + +.. _doubles: +.. _float: +.. _double: + +* The **parser<double>** and **parser<float> specializations** use the standard + C ``strtod`` function to convert floating point strings into floating point + values. As such, a broad range of string formats is supported, including + exponential notation (ex: ``1.7e15``) and properly supports locales. + +.. _Extension Guide: +.. _extending the library: + +Extension Guide +=============== + +Although the CommandLine library has a lot of functionality built into it +already (as discussed previously), one of its true strengths lie in its +extensibility. This section discusses how the CommandLine library works under +the covers and illustrates how to do some simple, common, extensions. + +.. _Custom parsers: +.. _custom parser: +.. _Writing a Custom Parser: + +Writing a custom parser +----------------------- + +One of the simplest and most common extensions is the use of a custom parser. +As `discussed previously`_, parsers are the portion of the CommandLine library +that turns string input from the user into a particular parsed data type, +validating the input in the process. + +There are two ways to use a new parser: + +#. Specialize the `cl::parser`_ template for your custom data type. + + This approach has the advantage that users of your custom data type will + automatically use your custom parser whenever they define an option with a + value type of your data type. The disadvantage of this approach is that it + doesn't work if your fundamental data type is something that is already + supported. + +#. Write an independent class, using it explicitly from options that need it. + + This approach works well in situations where you would line to parse an + option using special syntax for a not-very-special data-type. The drawback + of this approach is that users of your parser have to be aware that they are + using your parser instead of the builtin ones. + +To guide the discussion, we will discuss a custom parser that accepts file +sizes, specified with an optional unit after the numeric size. For example, we +would like to parse "102kb", "41M", "1G" into the appropriate integer value. In +this case, the underlying data type we want to parse into is '``unsigned``'. We +choose approach #2 above because we don't want to make this the default for all +``unsigned`` options. + +To start out, we declare our new ``FileSizeParser`` class: + +.. code-block:: c++ + + struct FileSizeParser : public cl::basic_parser<unsigned> { + // parse - Return true on error. + bool parse(cl::Option &O, const char *ArgName, const std::string &ArgValue, + unsigned &Val); + }; + +Our new class inherits from the ``cl::basic_parser`` template class to fill in +the default, boiler plate code for us. We give it the data type that we parse +into, the last argument to the ``parse`` method, so that clients of our custom +parser know what object type to pass in to the parse method. (Here we declare +that we parse into '``unsigned``' variables.) + +For most purposes, the only method that must be implemented in a custom parser +is the ``parse`` method. The ``parse`` method is called whenever the option is +invoked, passing in the option itself, the option name, the string to parse, and +a reference to a return value. If the string to parse is not well-formed, the +parser should output an error message and return true. Otherwise it should +return false and set '``Val``' to the parsed value. In our example, we +implement ``parse`` as: + +.. code-block:: c++ + + bool FileSizeParser::parse(cl::Option &O, const char *ArgName, + const std::string &Arg, unsigned &Val) { + const char *ArgStart = Arg.c_str(); + char *End; + + // Parse integer part, leaving 'End' pointing to the first non-integer char + Val = (unsigned)strtol(ArgStart, &End, 0); + + while (1) { + switch (*End++) { + case 0: return false; // No error + case 'i': // Ignore the 'i' in KiB if people use that + case 'b': case 'B': // Ignore B suffix + break; + + case 'g': case 'G': Val *= 1024*1024*1024; break; + case 'm': case 'M': Val *= 1024*1024; break; + case 'k': case 'K': Val *= 1024; break; + + default: + // Print an error message if unrecognized character! + return O.error("'" + Arg + "' value invalid for file size argument!"); + } + } + } + +This function implements a very simple parser for the kinds of strings we are +interested in. Although it has some holes (it allows "``123KKK``" for example), +it is good enough for this example. Note that we use the option itself to print +out the error message (the ``error`` method always returns true) in order to get +a nice error message (shown below). Now that we have our parser class, we can +use it like this: + +.. code-block:: c++ + + static cl::opt<unsigned, false, FileSizeParser> + MFS("max-file-size", cl::desc("Maximum file size to accept"), + cl::value_desc("size")); + +Which adds this to the output of our program: + +:: + + OPTIONS: + -help - display available options (-help-hidden for more) + ... + -max-file-size=<size> - Maximum file size to accept + +And we can test that our parse works correctly now (the test program just prints +out the max-file-size argument value): + +:: + + $ ./test + MFS: 0 + $ ./test -max-file-size=123MB + MFS: 128974848 + $ ./test -max-file-size=3G + MFS: 3221225472 + $ ./test -max-file-size=dog + -max-file-size option: 'dog' value invalid for file size argument! + +It looks like it works. The error message that we get is nice and helpful, and +we seem to accept reasonable file sizes. This wraps up the "custom parser" +tutorial. + +Exploiting external storage +--------------------------- + +Several of the LLVM libraries define static ``cl::opt`` instances that will +automatically be included in any program that links with that library. This is +a feature. However, sometimes it is necessary to know the value of the command +line option outside of the library. In these cases the library does or should +provide an external storage location that is accessible to users of the +library. Examples of this include the ``llvm::DebugFlag`` exported by the +``lib/Support/Debug.cpp`` file and the ``llvm::TimePassesIsEnabled`` flag +exported by the ``lib/VMCore/PassManager.cpp`` file. + +.. todo:: + + TODO: complete this section + +.. _dynamically loaded options: + +Dynamically adding command line options + +.. todo:: + + TODO: fill in this section diff --git a/docs/programming.rst b/docs/programming.rst index add923f899..27e43014ee 100644 --- a/docs/programming.rst +++ b/docs/programming.rst @@ -7,6 +7,7 @@ Programming Documentation :hidden: CodingStandards + CommandLine * `LLVM Language Reference Manual <LangRef.html>`_ @@ -18,7 +19,7 @@ Programming Documentation Introduction to the general layout of the LLVM sourcebase, important classes and APIs, and some tips & tricks. -* `CommandLine library Reference Manual <CommandLine.html>`_ +* :ref:`commandline` Provides information on using the command line parsing library. |