path: root/man3p/wscanf.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FWSCANF" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fwscanf 
.SH NAME
fwscanf, swscanf, wscanf \- convert formatted wide-character input
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
#include <wchar.h>
.br
.sp
int fwscanf(FILE *restrict\fP \fIstream\fP\fB, const wchar_t *restrict\fP
\fIformat\fP\fB, ... );
.br
int swscanf(const wchar_t *restrict\fP \fIws\fP\fB,
.br
\ \ \ \ \ \  const wchar_t *restrict\fP \fIformat\fP\fB, ... );
.br
int wscanf(const wchar_t *restrict\fP \fIformat\fP\fB, ... );
.br
\fP
.SH DESCRIPTION
.LP
The \fIfwscanf\fP() function shall read from the named input \fIstream\fP.
The \fIwscanf\fP() function shall read from the
standard input stream \fIstdin\fP. The \fIswscanf\fP() function shall
read from the wide-character string \fIws\fP. Each
function reads wide characters, interprets them according to a format,
and stores the results in its arguments. Each expects, as
arguments, a control wide-character string \fIformat\fP described
below, and a set of \fIpointer\fP arguments indicating where
the converted input should be stored. The result is undefined if there
are insufficient arguments for the format. If the
\fIformat\fP is exhausted while arguments remain, the excess arguments
are 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 wide character \fB%\fP
(see below) is replaced by the sequence \fB"%n$"\fP ,
where \fIn\fP is a decimal integer in the range [1,{NL_ARGMAX}]. This
feature provides for the definition of \fIformat\fP
wide-character strings that select arguments in an order appropriate
to specific languages. In \fIformat\fP wide-character strings
containing the \fB"%\fP\fIn\fP\fB$"\fP form of conversion specifications,
it is unspecified whether numbered arguments in
the argument list can be referenced from the \fIformat\fP wide-character
string more than once.
.LP
The \fIformat\fP can contain either form of a conversion specification-that
is, \fB%\fP or \fB"%\fP\fIn\fP\fB$"\fP-
but the two forms cannot normally be mixed within a single \fIformat\fP
wide-character string. The only exception to this is that
\fB%%\fP or \fB%*\fP can be mixed with the \fB"%\fP\fIn\fP\fB$"\fP
form. When numbered argument specifications are
used, specifying the \fIN\fPth argument requires that all the leading
arguments, from the first to the ( \fIN\fP-1)th, are
pointers. 
.LP
The
\fIfwscanf\fP() function in all its forms allows for detection of
a language-dependent radix character in the input string,
encoded as a wide-character value. 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
The \fIformat\fP is a wide-character string composed of zero or more
directives. Each directive is composed of one of the
following: one or more white-space wide characters ( <space>s, <tab>s,
<newline>s, <vertical-tab>s, or
<form-feed>s); an ordinary wide character (neither \fB'%'\fP nor a
white-space character); or a conversion specification.
Each conversion specification is introduced by a \fB'%'\fP   \ or
the sequence \fB"%\fP\fIn\fP\fB$"\fP  after which the following appear
in sequence:
.IP " *" 3
An optional assignment-suppressing character \fB'*'\fP .
.LP
.IP " *" 3
An optional non-zero decimal integer that specifies the maximum field
width.
.LP
.IP " *" 3
An optional length modifier that specifies the size of the receiving
object.
.LP
.IP " *" 3
A conversion specifier wide character that specifies the type of conversion
to be applied. The valid conversion specifiers are
described below.
.LP
.LP
The \fIfwscanf\fP() functions shall execute each directive of the
format in turn. If a directive fails, as detailed below, the
function shall return. Failures are described as input failures (due
to the unavailability of input bytes) or matching failures
(due to inappropriate input).
.LP
A directive composed of one or more white-space wide characters is
executed by reading input until no more valid input can be
read, or up to the first wide character which is not a white-space
wide character, which remains unread.
.LP
A directive that is an ordinary wide character shall be executed as
follows. The next wide character is read from the input and
compared with the wide character that comprises the directive; if
the comparison shows that they are not equivalent, the directive
shall fail, and the differing and subsequent wide characters remain
unread. Similarly, if end-of-file, an encoding error, or a read
error prevents a wide character from being read, the directive shall
fail.
.LP
A directive that is a conversion specification defines a set of matching
input sequences, as described below for each conversion
wide character. A conversion specification is executed in the following
steps.
.LP
Input white-space wide characters (as specified by \fIiswspace\fP()
) shall be skipped, unless the
conversion specification includes a \fB[\fP , \fBc\fP , or \fBn\fP
conversion specifier.
.LP
An item shall be read from the input, unless the conversion specification
includes an \fBn\fP conversion specifier wide
character. An input item is defined as the longest sequence of input
wide characters, not exceeding any specified field width,
which is an initial subsequence of a matching sequence. The first
wide character, if any, after the input item shall remain unread.
If the length of the input item is zero, the execution of the conversion
specification shall fail; this condition is a matching
failure, unless end-of-file, an encoding error, or a read error prevented
input from the stream, in which case it is an input
failure.
.LP
Except in the case of a \fB%\fP conversion specifier, the input item
(or, in the case of a \fB%n\fP conversion
specification, the count of input wide characters) shall be converted
to a type appropriate to the conversion wide character. If
the input item is not a matching sequence, the execution of the conversion
specification shall fail; this condition is a matching
failure. Unless assignment suppression was indicated by a \fB'*'\fP
, the result of the conversion shall be placed in the object
pointed to by the first argument following the \fIformat\fP argument
that has not already received a conversion result if the
conversion specification is introduced by \fB%\fP ,   \ or in the
\fIn\fPth argument if introduced by the wide-character
sequence \fB"%\fP\fIn\fP\fB$"\fP.  If this object does not
have an appropriate type, or if the result of the conversion cannot
be represented in the space provided, the behavior is
undefined.
.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 , \fBX\fP , or \fBn\fP
conversion specifier applies to an argument with type pointer to \fBsigned
char\fP or \fBunsigned char\fP.
.TP 7
\fBh\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , \fBX\fP , or \fBn\fP
conversion specifier applies to an argument with type pointer to \fBshort\fP
or \fBunsigned short\fP.
.TP 7
\fBl\fP\ (ell)
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , \fBX\fP , or \fBn\fP
conversion specifier applies to an argument with type pointer to \fBlong\fP
or \fBunsigned long\fP; that a following \fBa\fP ,
\fBA\fP , \fBe\fP , \fBE\fP , \fBf\fP , \fBF\fP , \fBg\fP , or \fBG\fP
conversion specifier applies to an
argument with type pointer to \fBdouble\fP; or that a following \fBc\fP
, \fBs\fP , or \fB[\fP conversion specifier
applies to an argument with type pointer to \fBwchar_t\fP.
.TP 7
\fBll\fP\ (ell-ell)
.sp
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , \fBX\fP , or \fBn\fP conversion
specifier applies to an argument with type pointer to \fBlong long\fP
or \fBunsigned long long\fP.
.TP 7
\fBj\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , \fBX\fP , or \fBn\fP
conversion specifier applies to an argument with type pointer to \fBintmax_t\fP
or \fBuintmax_t\fP.
.TP 7
\fBz\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , \fBX\fP , or \fBn\fP
conversion specifier applies to an argument with type pointer to \fBsize_t\fP
or the corresponding signed integer type.
.TP 7
\fBt\fP
Specifies that a following \fBd\fP , \fBi\fP , \fBo\fP , \fBu\fP ,
\fBx\fP , \fBX\fP , or \fBn\fP
conversion specifier applies to an argument with type pointer to \fBptrdiff_t\fP
or the corresponding \fBunsigned\fP type.
.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 an argument with type pointer
to \fBlong double\fP.
.sp
.LP
If a length modifier appears with any conversion specifier other than
as specified above, the behavior is undefined.
.LP
The following conversion specifier wide characters are valid:
.TP 7
\fBd\fP
Matches an optionally signed decimal integer, whose format is the
same as expected for the subject sequence of \fIwcstol\fP() with the
value 10 for the \fIbase\fP argument. In the absence of a size modifier,
the application shall ensure that the corresponding argument is a
pointer to \fBint\fP.
.TP 7
\fBi\fP
Matches an optionally signed integer, whose format is the same as
expected for the subject sequence of \fIwcstol\fP() with 0 for the
\fIbase\fP argument. In the absence of a size modifier, the
application shall ensure that the corresponding argument is a pointer
to \fBint\fP.
.TP 7
\fBo\fP
Matches an optionally signed octal integer, whose format is the same
as expected for the subject sequence of \fIwcstoul\fP() with the value
8 for the \fIbase\fP argument. In the absence of a size modifier,
the application shall ensure that the corresponding argument is a
pointer to \fBunsigned\fP.
.TP 7
\fBu\fP
Matches an optionally signed decimal integer, whose format is the
same as expected for the subject sequence of \fIwcstoul\fP() with
the value 10 for the \fIbase\fP argument. In the absence of a size
modifier,
the application shall ensure that the corresponding argument is a
pointer to \fBunsigned\fP.
.TP 7
\fBx\fP
Matches an optionally signed hexadecimal integer, whose format is
the same as expected for the subject sequence of \fIwcstoul\fP() with
the value 16 for the \fIbase\fP argument. In the absence of a size
modifier,
the application shall ensure that the corresponding argument is a
pointer to \fBunsigned\fP.
.TP 7
\fBa\fP,\ \fBe\fP,\ \fBf\fP,\ \fBg\fP
.sp
Matches an optionally signed floating-point number, infinity, or NaN
whose format is the same as expected for the subject sequence
of \fIwcstod\fP(). In the absence of a size modifier, the application
shall ensure that the
corresponding argument is a pointer to \fBfloat\fP. 
.LP
If the \fIfwprintf\fP() family of functions generates character string
representations
for infinity and NaN (a symbolic entity encoded in floating-point
format) to support IEEE\ Std\ 754-1985, the
\fIfwscanf\fP() family of functions shall recognize them as input.
.TP 7
\fBs\fP
Matches a sequence of non white-space wide characters. If no \fBl\fP
(ell) qualifier is present, characters from the input
field shall be converted as if by repeated calls 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. The
application shall ensure that the corresponding argument is a pointer
to a character array large enough to accept the sequence and
the terminating null character, which shall be added automatically.
.LP
Otherwise, the application shall ensure that the corresponding argument
is a pointer to an array of \fBwchar_t\fP large enough
to accept the sequence and the terminating null wide character, which
shall be added automatically.
.TP 7
\fB[\fP
Matches a non-empty sequence of wide characters from a set of expected
wide characters (the \fIscanset\fP). If no \fBl\fP
(ell) qualifier is present, wide characters from the input field shall
be converted as if by repeated calls 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.
The application shall ensure that the corresponding argument is a
pointer to a character array large enough to accept the sequence and
the terminating null character, which shall be added
automatically. 
.LP
If an \fBl\fP (ell) qualifier is present, the application shall ensure
that the corresponding argument is a pointer to an
array of \fBwchar_t\fP large enough to accept the sequence and the
terminating null wide character, which shall be added
automatically.
.LP
The conversion specification includes all subsequent wide characters
in the \fIformat\fP string up to and including the
matching right square bracket ( \fB']'\fP ). The wide characters between
the square brackets (the \fIscanlist\fP) comprise the
scanset, unless the wide character after the left square bracket is
a circumflex ( \fB'^'\fP ), in which case the scanset
contains all wide characters that do not appear in the scanlist between
the circumflex and the right square bracket. If the
conversion specification begins with \fB"[]"\fP or \fB"[^]"\fP , the
right square bracket is included in the scanlist and the
next right square bracket is the matching right square bracket that
ends the conversion specification; otherwise, the first right
square bracket is the one that ends the conversion specification.
If a \fB'-'\fP is in the scanlist and is not the first wide
character, nor the second where the first wide character is a \fB'^'\fP
, nor the last wide character, the behavior is
implementation-defined.
.TP 7
\fBc\fP
Matches a sequence of wide characters of exactly the number specified
by the field width (1 if no field width is present in the
conversion specification). 
.LP
If no \fBl\fP (ell) length modifier is present, characters from the
input field shall be converted as if by repeated calls 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.
The corresponding argument shall be a pointer to the
initial element of a character array large enough to accept the sequence.
No null character is added.
.LP
If an \fBl\fP (ell) length modifier is present, the corresponding
argument shall be a pointer to the initial element of an
array of \fBwchar_t\fP large enough to accept the sequence. No null
wide character is added.
.LP
Otherwise, the application shall ensure that the corresponding argument
is a pointer to an array of \fBwchar_t\fP large enough
to accept the sequence. No null wide character is added.
.TP 7
\fBp\fP
Matches an implementation-defined set of sequences, which shall be
the same as the set of sequences that is produced by the
\fB%p\fP conversion specification of the corresponding \fIfwprintf\fP()
functions. The
application shall ensure that the corresponding argument is a pointer
to a pointer to \fBvoid\fP. The interpretation of the input
item is implementation-defined. If the input item is a value converted
earlier during the same program execution, the pointer that
results shall compare equal to that value; otherwise, the behavior
of the \fB%p\fP conversion is undefined.
.TP 7
\fBn\fP
No input is consumed. The application shall ensure that the corresponding
argument is a pointer to the integer into which is to
be written the number of wide characters read from the input so far
by this call to the \fIfwscanf\fP() functions. Execution of a
\fB%n\fP conversion specification shall not increment the assignment
count returned at the completion of execution of the
function. No argument shall be converted, but one shall be consumed.
If the conversion specification includes an
assignment-suppressing wide character or a field width, the behavior
is undefined.
.TP 7
\fBC\fP
Equivalent to \fBlc\fP . 
.TP 7
\fBS\fP
Equivalent to \fBls\fP . 
.TP 7
\fB%\fP
Matches a single \fB'%'\fP wide character; no conversion or assignment
shall occur. The complete conversion specification
shall be \fB%%\fP .
.sp
.LP
If a conversion specification is invalid, the behavior is undefined.
.LP
The conversion specifiers \fBA\fP , \fBE\fP , \fBF\fP , \fBG\fP ,
and \fBX\fP are also valid and shall be
equivalent to, respectively, \fBa\fP , \fBe\fP , \fBf\fP , \fBg\fP
, and \fBx\fP .
.LP
If end-of-file is encountered during input, conversion is terminated.
If end-of-file occurs before any wide characters matching
the current conversion specification (except for \fB%n\fP ) have been
read (other than leading white-space, where permitted),
execution of the current conversion specification shall terminate
with an input failure. Otherwise, unless execution of the current
conversion specification is terminated with a matching failure, execution
of the following conversion specification (if any) shall
be terminated with an input failure.
.LP
Reaching the end of the string in \fIswscanf\fP() shall be equivalent
to encountering end-of-file for \fIfwscanf\fP().
.LP
If conversion terminates on a conflicting input, the offending input
shall be left unread in the input. Any trailing white space
(including <newline>) shall be left unread unless matched by a conversion
specification. The success of literal matches and
suppressed assignments is only directly determinable via the \fB%n\fP
conversion specification.
.LP
The
\fIfwscanf\fP() and \fIwscanf\fP() functions may mark the \fIst_atime\fP
field of the file associated with \fIstream\fP for
update. The \fIst_atime\fP field shall be marked for update by the
first successful execution of \fIfgetc\fP(), \fIfgetwc\fP(), \fIfgets\fP(),
\fIfgetws\fP(), \fIfread\fP(), \fIgetc\fP(), \fIgetwc\fP(), \fIgetchar\fP(),
\fIgetwchar\fP(), \fIgets\fP(), \fIfscanf\fP(), or \fIfwscanf\fP()
using \fIstream\fP that returns data not supplied by a prior
call to \fIungetc\fP(). 
.SH RETURN VALUE
.LP
Upon successful completion, these functions shall return the number
of successfully matched and assigned input items; this
number can be zero in the event of an early matching failure. If the
input ends before the first matching failure or conversion,
EOF shall be returned. If a read error occurs, the error indicator
for the stream is set, EOF shall be returned,   \ and
\fIerrno\fP shall be set to indicate the error. 
.SH ERRORS
.LP
For the conditions under which the \fIfwscanf\fP() functions shall
fail and may fail, refer to \fIfgetwc\fP() .
.LP
In addition, \fIfwscanf\fP() may fail if:
.TP 7
.B EILSEQ
Input byte sequence does not form a valid character. 
.TP 7
.B EINVAL
There are insufficient arguments. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
The call:
.sp
.RS
.nf

\fBint i, n; float x; char name[50];
n = wscanf(L"%d%f%s", &i, &x, name);
\fP
.fi
.RE
.LP
with the input line:
.sp
.RS
.nf

\fB25 54.32E-1 Hamster
\fP
.fi
.RE
.LP
assigns to \fIn\fP the value 3, to \fIi\fP the value 25, to \fIx\fP
the value 5.432, and \fIname\fP contains the string
\fB"Hamster"\fP .
.LP
The call:
.sp
.RS
.nf

\fBint i; float x; char name[50];
(void) wscanf(L"%2d%f%*d %[0123456789]", &i, &x, name);
\fP
.fi
.RE
.LP
with input:
.sp
.RS
.nf

\fB56789 0123 56a72
\fP
.fi
.RE
.LP
assigns 56 to \fIi\fP, 789.0 to \fIx\fP, skips 0123, and places the
string \fB"56\\0"\fP in \fIname\fP. The next call to \fIgetchar\fP()
shall return the character \fB'a'\fP .
.SH APPLICATION USAGE
.LP
In format strings containing the \fB'%'\fP form of conversion specifications,
each argument in the argument list is used
exactly once.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIgetwc\fP() , \fIfwprintf\fP() , \fIsetlocale\fP() , \fIwcstod\fP()
, \fIwcstol\fP() ,
\fIwcstoul\fP() , \fIwcrtomb\fP() , the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Chapter 7, Locale, \fI<langinfo.h>\fP, \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 .