path: root/man3p/printf.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FPRINTF" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fprintf 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
fprintf, printf, snprintf, sprintf \- print formatted output
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
.sp
int fprintf(FILE *restrict\fP \fIstream\fP\fB, const char *restrict\fP
\fIformat\fP\fB, ...);
.br
int printf(const char *restrict\fP \fIformat\fP\fB, ...);
.br
int snprintf(char *restrict\fP \fIs\fP\fB, size_t\fP \fIn\fP\fB,
.br
\ \ \ \ \ \  const char *restrict\fP \fIformat\fP\fB, ...);
.br
int sprintf(char *restrict\fP \fIs\fP\fB, const char *restrict\fP
\fIformat\fP\fB, ...);
.br
\fP
.SH DESCRIPTION
.LP
The \fIfprintf\fP() function shall place output on the named output
\fIstream\fP. The \fIprintf\fP() function shall place
output on the standard output stream \fIstdout\fP. The \fIsprintf\fP()
function shall place output followed by the null byte,
\fB'\\0'\fP , in consecutive bytes starting at *\fIs\fP; it is the
user's responsibility to ensure that enough space is
available.
.LP
The \fIsnprintf\fP() function shall be equivalent to \fIsprintf\fP(),
with the addition of the \fIn\fP argument which states
the size of the buffer referred to by \fIs\fP. If \fIn\fP is zero,
nothing shall be written and \fIs\fP may be a null pointer.
Otherwise, output bytes beyond the \fIn\fP-1st shall be discarded
instead of being written to the array, and a null byte is
written at the end of the bytes actually written into the array.
.LP
If copying takes place between objects that overlap as a result of
a call to \fIsprintf\fP() or \fIsnprintf\fP(), the results
are undefined.
.LP
Each of these functions converts, formats, and prints its arguments
under control of the \fIformat\fP. The \fIformat\fP is a
character string, beginning and ending in its initial shift state,
if any. The \fIformat\fP is composed of zero or more
directives: \fIordinary characters\fP, which are simply copied to
the output stream, and \fIconversion specifications\fP, each of
which shall result in the fetching of zero or more arguments. The
results are undefined if there are insufficient arguments for the
\fIformat\fP. If the \fIformat\fP is exhausted while arguments remain,
the excess arguments shall be evaluated but are otherwise
ignored.
.LP
Conversions can be applied to the \fIn\fPth argument after the \fIformat\fP
in the argument list, rather than to the next unused
argument. In this case, the conversion specifier character \fB%\fP
(see below) is replaced by the sequence
\fB"%\fP\fIn\fP\fB$"\fP, where \fIn\fP is a decimal integer in the
range [1,{NL_ARGMAX}], giving the position of the
argument in the argument list. This feature provides for the definition
of format strings that select arguments in an order
appropriate to specific languages (see the EXAMPLES section).
.LP
The \fIformat\fP can contain either numbered argument conversion specifications
(that is, \fB"%\fP\fIn\fP\fB$"\fP and
\fB"*\fP\fIm\fP\fB$"\fP), or unnumbered argument conversion specifications
(that is, \fB%\fP and \fB*\fP ), but not
both. The only exception to this is that \fB%%\fP can be mixed with
the \fB"%\fP\fIn\fP\fB$"\fP form. The results of
mixing numbered and unnumbered argument specifications in a \fIformat\fP
string are undefined. When numbered argument
specifications are used, specifying the \fIN\fPth argument requires
that all the leading arguments, from the first to the
(\fIN-1\fP)th, are specified in the format string.
.LP
In format strings containing the \fB"%\fP\fIn\fP\fB$"\fP form of conversion
specification, numbered arguments in the
argument list can be referenced from the format string as many times
as required. 
.LP
In format strings containing the \fB%\fP form of conversion specification,
each conversion specification uses the first
unused argument in the argument list.
.LP
All
forms of the \fIfprintf\fP() functions allow for the insertion of
a language-dependent radix character in the output string. The
radix character is defined in the program's locale (category \fILC_NUMERIC
).\fP In the POSIX locale, or in a locale where the
radix character is not defined, the radix character shall default
to a period ( \fB'.'\fP ). 
.LP
Each conversion specification is introduced by the \fB'%'\fP character
\ or by the
character sequence \fB"%\fP\fIn\fP\fB$"\fP,  after which the
following appear in sequence:
.IP " *" 3
Zero or more \fIflags\fP (in any order), which modify the meaning
of the conversion specification.
.LP
.IP " *" 3
An optional minimum \fIfield width\fP. If the converted value has
fewer bytes than the field width, it shall be padded with
spaces by default on the left; it shall be padded on the right if
the left-adjustment flag ( \fB'-'\fP ), described below, is
given to the field width. The field width takes the form of an asterisk
( \fB'*'\fP ), described below, or a decimal
integer.
.LP
.IP " *" 3
An optional \fIprecision\fP that gives the minimum number of digits
to appear for the \fBd\fP , \fBi\fP , \fBo\fP ,
\fBu\fP , \fBx\fP , and \fBX\fP conversion specifiers; the number
of digits to appear after the radix character for the
\fBa\fP , \fBA\fP , \fBe\fP , \fBE\fP , \fBf\fP , and \fBF\fP conversion
specifiers; the maximum number of
significant digits for the \fBg\fP and \fBG\fP conversion specifiers;
or the maximum number of bytes to be printed from a
string in the \fBs\fP   \ and \fBS\fP  \ conversion
specifiers. The precision takes the form of a period ( \fB'.'\fP )
followed either by an asterisk ( \fB'*'\fP ), described
below, or an optional decimal digit string, where a null digit string
is treated as zero. If a precision appears with any other
conversion specifier, the behavior is undefined.
.LP
.IP " *" 3
An optional length modifier that specifies the size of the argument.
.LP
.IP " *" 3
A \fIconversion specifier\fP character that indicates the type of
conversion to be applied.
.LP
.LP
A field width, or precision, or both, may be indicated by an asterisk
( \fB'*'\fP ). In this case an argument of type
\fBint\fP supplies the field width or precision. Applications shall
ensure that arguments specifying field width, or precision, or
both appear in that order before the argument, if any, to be converted.
A negative field width is taken as a \fB'-'\fP flag
followed by a positive field width. A negative precision is taken
as if the precision were omitted.   \ In format
strings containing the \fB"%\fP\fIn\fP\fB$"\fP form of a conversion
specification, a field width or precision may be
indicated by the sequence \fB"*\fP\fIm\fP\fB$"\fP, where \fIm\fP is
a decimal integer in the range [1,{NL_ARGMAX}] giving
the position in the argument list (after the \fIformat\fP argument)
of an integer argument containing the field width or
precision, for example:
.sp
.RS
.nf

\fBprintf("%1$d:%2$.*3$d:%4$.*3$d\\n", hour, min, precision, sec);
\fP
.fi
.RE
.LP
The flag characters and their meanings are:
.TP 7
\fB'\fP
The integer portion of the result of a decimal conversion ( \fB%i\fP
, \fB%d\fP , \fB%u\fP , \fB%f\fP , \fB%F\fP ,
\fB%g\fP , or \fB%G\fP ) shall be formatted with thousands' grouping
characters. For other conversions the behavior is
undefined. The non-monetary grouping character is used. 
.TP 7
\fB-\fP
The result of the conversion shall be left-justified within the field.
The conversion is right-justified if this flag is not
specified.
.TP 7
\fB+\fP
The result of a signed conversion shall always begin with a sign (
\fB'+'\fP or \fB'-'\fP ). The conversion shall begin
with a sign only when a negative value is converted if this flag is
not specified.
.TP 7
<space>
If the first character of a signed conversion is not a sign or if
a signed conversion results in no characters, a <space>
shall be prefixed to the result. This means that if the <space> and
\fB'+'\fP flags both appear, the <space> flag
shall be ignored.
.TP 7
\fB#\fP
Specifies that the value is to be converted to an alternative form.
For \fBo\fP conversion, it increases the precision (if
necessary) to force the first digit of the result to be zero. For
\fBx\fP or \fBX\fP conversion specifiers, a non-zero result
shall have 0x (or 0X) prefixed to it. For \fBa\fP , \fBA\fP , \fBe\fP
, \fBE\fP , \fBf\fP , \fBF\fP , \fBg\fP
, and \fBG\fP conversion specifiers, the result shall always contain
a radix character, even if no digits follow the radix
character. Without this flag, a radix character appears in the result
of these conversions only if a digit follows it. For
\fBg\fP and \fBG\fP conversion specifiers, trailing zeros shall \fInot\fP
be removed from the result as they normally are.
For other conversion specifiers, the behavior is undefined.
.TP 7
\fB0\fP
For \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP , \fBx\fP , \fBX\fP , \fBa\fP
, \fBA\fP , \fBe\fP ,
\fBE\fP , \fBf\fP , \fBF\fP , \fBg\fP , and \fBG\fP conversion specifiers,
leading zeros (following any indication
of sign or base) are used to pad to the field width; no space padding
is performed. If the \fB'0'\fP and \fB'-'\fP flags both
appear, the \fB'0'\fP flag is ignored. For \fBd\fP , \fBi\fP , \fBo\fP
, \fBu\fP , \fBx\fP , and \fBX\fP
conversion specifiers, if a precision is specified, the \fB'0'\fP
flag is ignored.   \ If the
\fB'0'\fP and \fB'"\fP flags both appear, the grouping characters
are inserted before zero padding. For other conversions,
the behavior is undefined. 
.sp
.LP
The length modifiers and their meanings are:
.TP 7
\fBhh\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to a \fBsigned char\fP or \fBunsigned char\fP argument (the
argument will have been promoted according to the integer
promotions, but its value shall be converted to \fBsigned char\fP
or \fBunsigned char\fP before printing); or that a following
\fBn\fP conversion specifier applies to a pointer to a \fBsigned char\fP
argument.
.TP 7
\fBh\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to a \fBshort\fP or \fBunsigned short\fP argument (the argument
will have been promoted according to the integer
promotions, but its value shall be converted to \fBshort\fP or \fBunsigned
short\fP before printing); or that a following
\fBn\fP conversion specifier applies to a pointer to a \fBshort\fP
argument.
.TP 7
\fBl\fP\ (ell)
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to a \fBlong\fP or \fBunsigned long\fP argument; that a following
\fBn\fP conversion specifier applies to a pointer to
a \fBlong\fP argument; that a following \fBc\fP conversion specifier
applies to a \fBwint_t\fP argument; that a following
\fBs\fP conversion specifier applies to a pointer to a \fBwchar_t\fP
argument; or has no effect on a following \fBa\fP ,
\fBA\fP , \fBe\fP , \fBE\fP , \fBf\fP , \fBF\fP , \fBg\fP , or \fBG\fP
conversion specifier.
.TP 7
\fBll\fP\ (ell-ell)
.sp
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to a \fBlong long\fP or \fBunsigned long long\fP argument;
or that a following \fBn\fP conversion specifier applies to
a pointer to a \fBlong long\fP argument.
.TP 7
\fBj\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to an \fBintmax_t\fP or \fBuintmax_t\fP argument; or that
a following \fBn\fP conversion specifier applies to a
pointer to an \fBintmax_t\fP argument.
.TP 7
\fBz\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to a \fBsize_t\fP or the corresponding signed integer type
argument; or that a following \fBn\fP conversion specifier
applies to a pointer to a signed integer type corresponding to a \fBsize_t\fP
argument.
.TP 7
\fBt\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , or \fBX\fP conversion specifier
applies to a \fBptrdiff_t\fP or the corresponding \fBunsigned\fP type
argument; or that a following \fBn\fP conversion
specifier applies to a pointer to a \fBptrdiff_t\fP argument.
.TP 7
\fBL\fP
Specifies that a following \fBa\fP , \fBA\fP , \fBe\fP , \fBE\fP ,
\fBf\fP , \fBF\fP , \fBg\fP , or
\fBG\fP conversion specifier applies to a \fBlong double\fP argument.
.sp
.LP
If a length modifier appears with any conversion specifier other than
as specified above, the behavior is undefined.
.LP
The conversion specifiers and their meanings are:
.TP 7
\fBd\fP,\ \fBi\fP
The \fBint\fP argument shall be converted to a signed decimal in the
style \fB"[-]\fP\fIdddd\fP\fB"\fP. The precision
specifies the minimum number of digits to appear; if the value being
converted can be represented in fewer digits, it shall be
expanded with leading zeros. The default precision is 1. The result
of converting zero with an explicit precision of zero shall be
no characters.
.TP 7
\fBo\fP
The \fBunsigned\fP argument shall be converted to unsigned octal format
in the style \fB"\fP\fIdddd\fP\fB"\fP. The
precision specifies the minimum number of digits to appear; if the
value being converted can be represented in fewer digits, it
shall be expanded with leading zeros. The default precision is 1.
The result of converting zero with an explicit precision of zero
shall be no characters.
.TP 7
\fBu\fP
The \fBunsigned\fP argument shall be converted to unsigned decimal
format in the style \fB"\fP\fIdddd\fP\fB"\fP. The
precision specifies the minimum number of digits to appear; if the
value being converted can be represented in fewer digits, it
shall be expanded with leading zeros. The default precision is 1.
The result of converting zero with an explicit precision of zero
shall be no characters.
.TP 7
\fBx\fP
The \fBunsigned\fP argument shall be converted to unsigned hexadecimal
format in the style \fB"\fP\fIdddd\fP\fB"\fP;
the letters \fB"abcdef"\fP are used. The precision specifies the minimum
number of digits to appear; if the value being
converted can be represented in fewer digits, it shall be expanded
with leading zeros. The default precision is 1. The result of
converting zero with an explicit precision of zero shall be no characters.
.TP 7
\fBX\fP
Equivalent to the \fBx\fP conversion specifier, except that letters
\fB"ABCDEF"\fP are used instead of \fB"abcdef"\fP
\&.
.TP 7
\fBf\fP,\ \fBF\fP
The \fBdouble\fP argument shall be converted to decimal notation in
the style
\fB"[-]\fP\fIddd\fP\fB.\fP\fIddd\fP\fB"\fP, where the number of digits
after the radix character is equal to the
precision specification. If the precision is missing, it shall be
taken as 6; if the precision is explicitly zero and no
\fB'#'\fP flag is present, no radix character shall appear. If a radix
character appears, at least one digit appears before it.
The low-order digit shall be rounded in an implementation-defined
manner. 
.LP
A \fBdouble\fP argument representing an infinity shall be converted
in one of the styles \fB"[-]inf"\fP or
\fB"[-]infinity"\fP ; which style is implementation-defined. A \fBdouble\fP
argument representing a NaN shall be converted in
one of the styles \fB"[-]nan(\fP\fIn-char-sequence\fP\fB)"\fP or \fB"[-]nan"\fP
; which style, and the meaning of any
\fIn-char-sequence\fP, is implementation-defined. The \fBF\fP conversion
specifier produces \fB"INF"\fP ,
\fB"INFINITY"\fP , or \fB"NAN"\fP instead of \fB"inf"\fP , \fB"infinity"\fP
, or \fB"nan"\fP , respectively.
.TP 7
\fBe\fP,\ \fBE\fP
The \fBdouble\fP argument shall be converted in the style
\fB"[-]\fP\fId\fP\fB.\fP\fIddd\fP\fBe\(+-\fP\fIdd\fP\fB"\fP, where
there is one digit before the radix character
(which is non-zero if the argument is non-zero) and the number of
digits after it is equal to the precision; if the precision is
missing, it shall be taken as 6; if the precision is zero and no \fB'#'\fP
flag is present, no radix character shall appear. The
low-order digit shall be rounded in an implementation-defined manner.
The \fBE\fP conversion specifier shall produce a number
with \fB'E'\fP instead of \fB'e'\fP introducing the exponent. The
exponent shall always contain at least two digits. If the
value is zero, the exponent shall be zero. 
.LP
A \fBdouble\fP argument representing an infinity or NaN shall be converted
in the style of an \fBf\fP or \fBF\fP
conversion specifier.
.TP 7
\fBg\fP,\ \fBG\fP
The \fBdouble\fP argument shall be converted in the style \fBf\fP
or \fBe\fP (or in the style \fBF\fP or \fBE\fP
in the case of a \fBG\fP conversion specifier), with the precision
specifying the number of significant digits. If an explicit
precision is zero, it shall be taken as 1. The style used depends
on the value converted; style \fBe\fP (or \fBE\fP ) shall
be used only if the exponent resulting from such a conversion is less
than -4 or greater than or equal to the precision. Trailing
zeros shall be removed from the fractional portion of the result;
a radix character shall appear only if it is followed by a digit
or a \fB'#'\fP flag is present. 
.LP
A \fBdouble\fP argument representing an infinity or NaN shall be converted
in the style of an \fBf\fP or \fBF\fP
conversion specifier.
.TP 7
\fBa\fP,\ \fBA\fP
A \fBdouble\fP argument representing a floating-point number shall
be converted in the style
\fB"[-]0x\fP\fIh\fP\fB.\fP\fIhhhh\fP\fBp\(+-\fP\fId\fP\fB"\fP, where
there is one hexadecimal digit (which shall
be non-zero if the argument is a normalized floating-point number
and is otherwise unspecified) before the decimal-point character
and the number of hexadecimal digits after it is equal to the precision;
if the precision is missing and FLT_RADIX is a power of 2,
then the precision shall be sufficient for an exact representation
of the value; if the precision is missing and FLT_RADIX is not a
power of 2, then the precision shall be sufficient to distinguish
values of type \fBdouble\fP, except that trailing zeros may be
omitted; if the precision is zero and the \fB'#'\fP flag is not specified,
no decimal-point character shall appear. The letters
\fB"abcdef"\fP shall be used for \fBa\fP conversion and the letters
\fB"ABCDEF"\fP for \fBA\fP conversion. The
\fBA\fP conversion specifier produces a number with \fB'X'\fP and
\fB'P'\fP instead of \fB'x'\fP and \fB'p'\fP . The
exponent shall always contain at least one digit, and only as many
more digits as necessary to represent the decimal exponent of 2.
If the value is zero, the exponent shall be zero. 
.LP
A \fBdouble\fP argument representing an infinity or NaN shall be converted
in the style of an \fBf\fP or \fBF\fP
conversion specifier.
.TP 7
\fBc\fP
The \fBint\fP argument shall be converted to an \fBunsigned char\fP,
and the resulting byte shall be written. 
.LP
If an \fBl\fP (ell) qualifier is present, the \fBwint_t\fP argument
shall be converted as if by an \fBls\fP conversion
specification with no precision and an argument that points to a two-element
array of type \fBwchar_t\fP, the first element of
which contains the \fBwint_t\fP argument to the \fBls\fP conversion
specification and the second element contains a null wide
character.
.TP 7
\fBs\fP
The argument shall be a pointer to an array of \fBchar\fP. Bytes from
the array shall be written up to (but not including) any
terminating null byte. If the precision is specified, no more than
that many bytes shall be written. If the precision is not
specified or is greater than the size of the array, the application
shall ensure that the array contains a null byte. 
.LP
If an \fBl\fP (ell) qualifier is present, the argument shall be a
pointer to an array of type \fBwchar_t\fP. Wide characters
from the array shall be converted to characters (each as if by a call
to the \fIwcrtomb\fP() function, with the conversion state described
by an \fBmbstate_t\fP object
initialized to zero before the first wide character is converted)
up to and including a terminating null wide character. The
resulting characters shall be written up to (but not including) the
terminating null character (byte). If no precision is
specified, the application shall ensure that the array contains a
null wide character. If a precision is specified, no more than
that many characters (bytes) shall be written (including shift sequences,
if any), and the array shall contain a null wide
character if, to equal the character sequence length given by the
precision, the function would need to access a wide character one
past the end of the array. In no case shall a partial character be
written.
.TP 7
\fBp\fP
The argument shall be a pointer to \fBvoid\fP. The value of the pointer
is converted to a sequence of printable characters, in
an implementation-defined manner.
.TP 7
\fBn\fP
The argument shall be a pointer to an integer into which is written
the number of bytes written to the output so far by this
call to one of the \fIfprintf\fP() functions. No argument is converted.
.TP 7
\fBC\fP
Equivalent to \fBlc\fP . 
.TP 7
\fBS\fP
Equivalent to \fBls\fP . 
.TP 7
\fB%\fP
Print a \fB'%'\fP character; no argument is converted. The complete
conversion specification shall be \fB%%\fP .
.sp
.LP
If a conversion specification does not match one of the above forms,
the behavior is undefined. If any argument is not the
correct type for the corresponding conversion specification, the behavior
is undefined.
.LP
In no case shall a nonexistent or small field width cause truncation
of a field; if the result of a conversion is wider than the
field width, the field shall be expanded to contain the conversion
result. Characters generated by \fIfprintf\fP() and
\fIprintf\fP() are printed as if \fIfputc\fP() had been called.
.LP
For the \fBa\fP and \fBA\fP conversion specifiers, if FLT_RADIX is
a power of 2, the value shall be correctly rounded to a
hexadecimal floating number with the given precision.
.LP
For \fBa\fP and \fBA\fP conversions, if FLT_RADIX is not a power of
2 and the result is not exactly representable in the
given precision, the result should be one of the two adjacent numbers
in hexadecimal floating style with the given precision, with
the extra stipulation that the error should have a correct sign for
the current rounding direction.
.LP
For the \fBe\fP , \fBE\fP , \fBf\fP , \fBF\fP , \fBg\fP , and \fBG\fP
conversion specifiers, if the number of
significant decimal digits is at most DECIMAL_DIG, then the result
should be correctly rounded. If the number of significant
decimal digits is more than DECIMAL_DIG but the source value is exactly
representable with DECIMAL_DIG digits, then the result
should be an exact representation with trailing zeros. Otherwise,
the source value is bounded by two adjacent decimal strings
\fIL\fP < \fIU\fP, both having DECIMAL_DIG significant digits; the
value of the resultant decimal string \fID\fP should
satisfy \fIL\fP <= \fID\fP <= \fIU\fP, with the extra stipulation
that the error should have a correct sign for the
current rounding direction.
.LP
The
\fIst_ctime\fP and \fIst_mtime\fP fields of the file shall be marked
for update between the call to a successful execution of
\fIfprintf\fP() or \fIprintf\fP() and the next successful completion
of a call to \fIfflush\fP() or \fIfclose\fP() on the same stream or
a
call to \fIexit\fP() or \fIabort\fP(). 
.SH RETURN VALUE
.LP
Upon successful completion, the \fIfprintf\fP() and \fIprintf\fP()
functions shall return the number of bytes transmitted.
.LP
Upon successful completion, the \fIsprintf\fP() function shall return
the number of bytes written to \fIs\fP, excluding the
terminating null byte.
.LP
Upon successful completion, the \fIsnprintf\fP() function shall return
the number of bytes that would be written to \fIs\fP
had \fIn\fP been sufficiently large excluding the terminating null
byte.
.LP
If an output error was encountered, these functions shall return a
negative value.
.LP
If the value of \fIn\fP is zero on a call to \fIsnprintf\fP(), nothing
shall be written, the number of bytes that would have
been written had \fIn\fP been sufficiently large excluding the terminating
null shall be returned, and \fIs\fP may be a null
pointer.
.SH ERRORS
.LP
For the conditions under which \fIfprintf\fP() and \fIprintf\fP()
fail and may fail, refer to \fIfputc\fP() or \fIfputwc\fP() .
.LP
In addition, all forms of \fIfprintf\fP() may fail if:
.TP 7
.B EILSEQ
A wide-character code that does not correspond to a valid character
has been detected. 
.TP 7
.B EINVAL
There are insufficient arguments. 
.sp
.LP
The \fIprintf\fP() and \fIfprintf\fP() functions may fail if:
.TP 7
.B ENOMEM
Insufficient storage space is available. 
.sp
.LP
The \fIsnprintf\fP() function shall fail if:
.TP 7
.B EOVERFLOW
The value of \fIn\fP is greater than {INT_MAX} or the number of bytes
needed to hold the output excluding the terminating null is
greater than {INT_MAX}. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.SS Printing Language-Independent Date and Time
.LP
The following statement can be used to print date and time using a
language-independent format:
.sp
.RS
.nf

\fBprintf(format, weekday, month, day, hour, min);
\fP
.fi
.RE
.LP
For American usage, \fIformat\fP could be a pointer to the following
string:
.sp
.RS
.nf

\fB"%s, %s %d, %d:%.2d\\n"
\fP
.fi
.RE
.LP
This example would produce the following message:
.sp
.RS
.nf

\fBSunday, July 3, 10:02
\fP
.fi
.RE
.LP
For German usage, \fIformat\fP could be a pointer to the following
string:
.sp
.RS
.nf

\fB"%1$s, %3$d. %2$s, %4$d:%5$.2d\\n"
\fP
.fi
.RE
.LP
This definition of \fIformat\fP would produce the following message:
.sp
.RS
.nf

\fBSonntag, 3. Juli, 10:02
\fP
.fi
.RE
.SS Printing File Information
.LP
The following example prints information about the type, permissions,
and number of links of a specific file in a directory.
.LP
The first two calls to \fIprintf\fP() use data decoded from a previous
\fIstat\fP() call.
The user-defined \fIstrperm\fP() function shall return a string similar
to the one at the beginning of the output for the
following command:
.sp
.RS
.nf

\fBls -l
\fP
.fi
.RE
.LP
The next call to \fIprintf\fP() outputs the owner's name if it is
found using \fIgetpwuid\fP(); the \fIgetpwuid\fP() function shall
return a \fBpasswd\fP structure from which the name of the user is
extracted. If the user name is not found, the program instead
prints out the numeric value of the user ID.
.LP
The next call prints out the group name if it is found using \fIgetgrgid\fP();
\fIgetgrgid\fP() is very similar to \fIgetpwuid\fP() except that it
shall return group information based on the group number. Once
again, if the group is not found, the program prints the numeric value
of the group for the entry.
.LP
The final call to \fIprintf\fP() prints the size of the file.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <grp.h>
.sp

char *strperm (mode_t);
\&...
struct stat statbuf;
struct passwd *pwd;
struct group *grp;
\&...
printf("%10.10s", strperm (statbuf.st_mode));
printf("%4d", statbuf.st_nlink);
.sp

if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
    printf(" %-8.8s", pwd->pw_name);
else
    printf(" %-8ld", (long) statbuf.st_uid);
.sp

if ((grp = getgrgid(statbuf.st_gid)) != NULL)
    printf(" %-8.8s", grp->gr_name);
else
    printf(" %-8ld", (long) statbuf.st_gid);
.sp

printf("%9jd", (intmax_t) statbuf.st_size);
\&...
\fP
.fi
.RE
.SS Printing a Localized Date String
.LP
The following example gets a localized date string. The \fInl_langinfo\fP()
function shall return the localized date string, which specifies the
order and layout of the date. The \fIstrftime\fP() function takes
this information and, using the \fBtm\fP structure for values,
places the date and time information into \fIdatestring\fP. The \fIprintf\fP()
function then outputs \fIdatestring\fP and the
name of the entry.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <time.h>
#include <langinfo.h>
\&...
struct dirent *dp;
struct tm *tm;
char datestring[256];
\&...
strftime(datestring, sizeof(datestring), nl_langinfo (D_T_FMT), tm);
.sp

printf(" %s %s\\n", datestring, dp->d_name);
\&...
\fP
.fi
.RE
.SS Printing Error Information
.LP
The following example uses \fIfprintf\fP() to write error information
to standard error.
.LP
In the first group of calls, the program tries to open the password
lock file named \fBLOCKFILE\fP. If the file already exists,
this is an error, as indicated by the O_EXCL flag on the \fIopen\fP()
function. If the call
fails, the program assumes that someone else is updating the password
file, and the program exits.
.LP
The next group of calls saves a new password file as the current password
file by creating a link between \fBLOCKFILE\fP and
the new password file \fBPASSWDFILE\fP.
.sp
.RS
.nf

\fB#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
.sp

#define LOCKFILE "/etc/ptmp"
#define PASSWDFILE "/etc/passwd"
\&...
int pfd;
\&...
if ((pfd = open(LOCKFILE, O_WRONLY | O_CREAT | O_EXCL,
    S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)) == -1)
{
    fprintf(stderr, "Cannot open /etc/ptmp. Try again later.\\n");
    exit(1);
}
\&...
if (link(LOCKFILE,PASSWDFILE) == -1) {
    fprintf(stderr, "Link error: %s\\n", strerror(errno));
    exit(1);
}
\&...
\fP
.fi
.RE
.SS Printing Usage Information
.LP
The following example checks to make sure the program has the necessary
arguments, and uses \fIfprintf\fP() to print usage
information if the expected number of arguments is not present.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <stdlib.h>
\&...
char *Options = "hdbtl";
\&...
if (argc < 2) {
    fprintf(stderr, "Usage: %s -%s <file\\n", argv[0], Options); exit(1);
}
\&...
\fP
.fi
.RE
.SS Formatting a Decimal String
.LP
The following example prints a key and data pair on \fIstdout\fP.
Note use of the \fB'*'\fP (asterisk) in the format string;
this ensures the correct number of decimal places for the element
based on the number of elements requested.
.sp
.RS
.nf

\fB#include <stdio.h>
\&...
long i;
char *keystr;
int elementlen, len;
\&...
while (len < elementlen) {
\&...
    printf("%s Element%0*ld\\n", keystr, elementlen, i);
\&...
}
\fP
.fi
.RE
.SS Creating a Filename
.LP
The following example creates a filename using information from a
previous \fIgetpwnam\fP() function that returned the HOME directory
of the user.
.sp
.RS
.nf

\fB#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
\&...
char filename[PATH_MAX+1];
struct passwd *pw;
\&...
sprintf(filename, "%s/%d.out", pw->pw_dir, getpid());
\&...
\fP
.fi
.RE
.SS Reporting an Event
.LP
The following example loops until an event has timed out. The \fIpause\fP()
function
waits forever unless it receives a signal. The \fIfprintf\fP() statement
should never occur due to the possible return values of
\fIpause\fP().
.sp
.RS
.nf

\fB#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
\&...
while (!event_complete) {
\&...
    if (pause() != -1 || errno != EINTR)
        fprintf(stderr, "pause: unknown error: %s\\n", strerror(errno));
}
\&...
\fP
.fi
.RE
.SS Printing Monetary Information
.LP
The following example uses \fIstrfmon\fP() to convert a number and
store it as a
formatted monetary string named \fIconvbuf\fP. If the first number
is printed, the program prints the format and the description;
otherwise, it just prints the number.
.sp
.RS
.nf

\fB#include <monetary.h>
#include <stdio.h>
\&...
struct tblfmt {
    char *format;
    char *description;
};
.sp

struct tblfmt table[] = {
    { "%n", "default formatting" },
    { "%11n", "right align within an 11 character field" },
    { "%#5n", "aligned columns for values up to 99999" },
    { "%=*#5n", "specify a fill character" },
    { "%=0#5n", "fill characters do not use grouping" },
    { "%^#5n", "disable the grouping separator" },
    { "%^#5.0n", "round off to whole units" },
    { "%^#5.4n", "increase the precision" },
    { "%(#5n", "use an alternative pos/neg style" },
    { "%!(#5n", "disable the currency symbol" },
};
\&...
float input[3];
int i, j;
char convbuf[100];
\&...
strfmon(convbuf, sizeof(convbuf), table[i].format, input[j]);
.sp

if (j == 0) {
    printf("%s  %s  %s\\n", table[i].format,
        convbuf, table[i].description);
}
else {
    printf("    %s\\n", convbuf);
}
\&...
\fP
.fi
.RE
.SS Printing Wide Characters
.LP
The following example prints a series of wide characters. Suppose
that \fB"L`@`"\fP expands to three bytes:
.sp
.RS
.nf

\fBwchar_t wz [3] = L"@@";       // Zero-terminated
wchar_t wn [3] = L"@@@";      // Unterminated
.sp

fprintf (stdout,"%ls", wz);   // Outputs 6 bytes
fprintf (stdout,"%ls", wn);   // Undefined because wn has no terminator
fprintf (stdout,"%4ls", wz);  // Outputs 3 bytes
fprintf (stdout,"%4ls", wn);  // Outputs 3 bytes; no terminator needed
fprintf (stdout,"%9ls", wz);  // Outputs 6 bytes
fprintf (stdout,"%9ls", wn);  // Outputs 9 bytes; no terminator needed
fprintf (stdout,"%10ls", wz); // Outputs 6 bytes
fprintf (stdout,"%10ls", wn); // Undefined because wn has no terminator
\fP
.fi
.RE
.LP
In the last line of the example, after processing three characters,
nine bytes have been output. The fourth character must then
be examined to determine whether it converts to one byte or more.
If it converts to more than one byte, the output is only nine
bytes. Since there is no fourth character in the array, the behavior
is undefined.
.SH APPLICATION USAGE
.LP
If the application calling \fIfprintf\fP() has any objects of type
\fBwint_t\fP or \fBwchar_t\fP, it must also include the \fI<wchar.h>\fP
header to have these objects defined.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIfputc\fP() , \fIfscanf\fP() , \fIsetlocale\fP() , \fIstrfmon\fP()
, \fIwcrtomb\fP()
, the Base Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter 7,
Locale, \fI<stdio.h>\fP, \fI<wchar.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .