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FWSCANF(3P) POSIX Programmer's Manual FWSCANF(3P)
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (con-
sult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on
Linux.
NAME
fwscanf, swscanf, wscanf - convert formatted wide-character input
SYNOPSIS
#include <stdio.h>
#include <wchar.h>
int fwscanf(FILE *restrict stream, const wchar_t *restrict format, ... );
int swscanf(const wchar_t *restrict ws,
const wchar_t *restrict format, ... );
int wscanf(const wchar_t *restrict format, ... );
DESCRIPTION
The fwscanf() function shall read from the named input stream. The wscanf() function shall read from the standard input
stream stdin. The swscanf() function shall read from the wide-character string ws. 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 format described below, and a set of pointer arguments indicating where the converted input should
be stored. The result is undefined if there are insufficient arguments for the format. If the format is exhausted while
arguments remain, the excess arguments are evaluated but are otherwise ignored.
Conversions can be applied to the nth argument after the format in the argument list, rather than to the next unused
argument. In this case, the conversion specifier wide character % (see below) is replaced by the sequence "%n$", where n
is a decimal integer in the range [1,{NL_ARGMAX}]. This feature provides for the definition of format wide-character
strings that select arguments in an order appropriate to specific languages. In format wide-character strings containing
the "%n$" form of conversion specifications, it is unspecified whether numbered arguments in the argument list can be
referenced from the format wide-character string more than once.
The format can contain either form of a conversion specification-that is, % or "%n$"- but the two forms cannot normally
be mixed within a single format wide-character string. The only exception to this is that %% or %* can be mixed with the
"%n$" form. When numbered argument specifications are used, specifying the Nth argument requires that all the leading
arguments, from the first to the ( N-1)th, are pointers.
The fwscanf() 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 LC_NUMERIC ). In the
POSIX locale, or in a locale where the radix character is not defined, the radix character shall default to a period (
'.' ).
The format is a wide-character string composed of zero or more directives. Each directive is composed of one of the fol-
lowing: 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 '%' nor a white-space character); or a conversion specification. Each conversion speci-
fication is introduced by a '%' or the sequence "%n$" after which the following appear in sequence:
* An optional assignment-suppressing character '*' .
* An optional non-zero decimal integer that specifies the maximum field width.
* An optional length modifier that specifies the size of the receiving object.
* A conversion specifier wide character that specifies the type of conversion to be applied. The valid conversion speci-
fiers are described below.
The fwscanf() 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).
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.
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 equiv-
alent, 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.
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.
Input white-space wide characters (as specified by iswspace() ) shall be skipped, unless the conversion specification
includes a [, c, or n conversion specifier.
An item shall be read from the input, unless the conversion specification includes an n conversion specifier wide charac-
ter. 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.
Except in the case of a % conversion specifier, the input item (or, in the case of a %n 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 '*', the result of the conversion shall be placed in the object
pointed to by the first argument following the format argument that has not already received a conversion result if the
conversion specification is introduced by %, or in the nth argument if introduced by the wide-character sequence "%n$".
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.
The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
signed char or unsigned char.
h Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
short or unsigned short.
l (ell)
Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
long or unsigned long; that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with
type pointer to double; or that a following c, s, or [ conversion specifier applies to an argument with type
pointer to wchar_t.
ll (ell-ell)
Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
long long or unsigned long long.
j Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
intmax_t or uintmax_t.
z Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
size_t or the corresponding signed integer type.
t Specifies that a following d, i, o, u, x, X, or n conversion specifier applies to an argument with type pointer to
ptrdiff_t or the corresponding unsigned type.
L Specifies that a following a, A, e, E, f, F, g, or G conversion specifier applies to an argument with type pointer
to long double.
If a length modifier appears with any conversion specifier other than as specified above, the behavior is undefined.
The following conversion specifier wide characters are valid:
d Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of
wcstol() with the value 10 for the base argument. In the absence of a size modifier, the application shall ensure
that the corresponding argument is a pointer to int.
i Matches an optionally signed integer, whose format is the same as expected for the subject sequence of wcstol()
with 0 for the base argument. In the absence of a size modifier, the application shall ensure that the correspond-
ing argument is a pointer to int.
o Matches an optionally signed octal integer, whose format is the same as expected for the subject sequence of
wcstoul() with the value 8 for the base argument. In the absence of a size modifier, the application shall ensure
that the corresponding argument is a pointer to unsigned.
u Matches an optionally signed decimal integer, whose format is the same as expected for the subject sequence of
wcstoul() with the value 10 for the base argument. In the absence of a size modifier, the application shall ensure
that the corresponding argument is a pointer to unsigned.
x Matches an optionally signed hexadecimal integer, whose format is the same as expected for the subject sequence of
wcstoul() with the value 16 for the base argument. In the absence of a size modifier, the application shall ensure
that the corresponding argument is a pointer to unsigned.
a, e, f, g
Matches an optionally signed floating-point number, infinity, or NaN whose format is the same as expected for the
subject sequence of wcstod(). In the absence of a size modifier, the application shall ensure that the correspond-
ing argument is a pointer to float.
If the fwprintf() 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 fwscanf() family of functions shall recognize them as
input.
s Matches a sequence of non white-space wide characters. If no l (ell) qualifier is present, characters from the
input field shall be converted as if by repeated calls to the wcrtomb() function, with the conversion state
described by an mbstate_t 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.
Otherwise, the application shall ensure that the corresponding argument is a pointer to an array of wchar_t large enough
to accept the sequence and the terminating null wide character, which shall be added automatically.
[ Matches a non-empty sequence of wide characters from a set of expected wide characters (the scanset). If no l
(ell) qualifier is present, wide characters from the input field shall be converted as if by repeated calls to the
wcrtomb() function, with the conversion state described by an mbstate_t 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 auto-
matically.
If an l (ell) qualifier is present, the application shall ensure that the corresponding argument is a pointer to an array
of wchar_t large enough to accept the sequence and the terminating null wide character, which shall be added automati-
cally.
The conversion specification includes all subsequent wide characters in the format string up to and including the match-
ing right square bracket ( ']' ). The wide characters between the square brackets (the scanlist) comprise the scanset,
unless the wide character after the left square bracket is a circumflex ( '^' ), 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 "[]" or "[^]", 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 '-' is in the scanlist and is not the first wide charac-
ter, nor the second where the first wide character is a '^', nor the last wide character, the behavior is implementation-
defined.
c 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).
If no l (ell) length modifier is present, characters from the input field shall be converted as if by repeated calls to
the wcrtomb() function, with the conversion state described by an mbstate_t 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.
If an l (ell) length modifier is present, the corresponding argument shall be a pointer to the initial element of an
array of wchar_t large enough to accept the sequence. No null wide character is added.
Otherwise, the application shall ensure that the corresponding argument is a pointer to an array of wchar_t large enough
to accept the sequence. No null wide character is added.
p Matches an implementation-defined set of sequences, which shall be the same as the set of sequences that is pro-
duced by the %p conversion specification of the corresponding fwprintf() functions. The application shall ensure
that the corresponding argument is a pointer to a pointer to void. The interpretation of the input item is imple-
mentation-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 %p conversion is undefined.
n 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 fwscanf()
functions. Execution of a %n 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 con-
version specification includes an assignment-suppressing wide character or a field width, the behavior is unde-
fined.
C Equivalent to lc .
S Equivalent to ls .
% Matches a single '%' wide character; no conversion or assignment shall occur. The complete conversion specifica-
tion shall be %% .
If a conversion specification is invalid, the behavior is undefined.
The conversion specifiers A, E, F, G, and X are also valid and shall be equivalent to, respectively, a, e, f, g, and x .
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 %n ) have been read (other than leading white-space, where per-
mitted), execution of the current conversion specification shall terminate with an input failure. Otherwise, unless exe-
cution of the current conversion specification is terminated with a matching failure, execution of the following conver-
sion specification (if any) shall be terminated with an input failure.
Reaching the end of the string in swscanf() shall be equivalent to encountering end-of-file for fwscanf().
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 lit-
eral matches and suppressed assignments is only directly determinable via the %n conversion specification.
The fwscanf() and wscanf() functions may mark the st_atime field of the file associated with stream for update. The
st_atime field shall be marked for update by the first successful execution of fgetc(), fgetwc(), fgets(), fgetws(),
fread(), getc(), getwc(), getchar(), getwchar(), gets(), fscanf(), or fwscanf() using stream that returns data not sup-
plied by a prior call to ungetc().
RETURN VALUE
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 errno shall be set to indicate the error.
ERRORS
For the conditions under which the fwscanf() functions shall fail and may fail, refer to fgetwc().
In addition, fwscanf() may fail if:
EILSEQ Input byte sequence does not form a valid character.
EINVAL There are insufficient arguments.
The following sections are informative.
EXAMPLES
The call:
int i, n; float x; char name[50];
n = wscanf(L"%d%f%s", &i, &x, name);
with the input line:
25 54.32E-1 Hamster
assigns to n the value 3, to i the value 25, to x the value 5.432, and name contains the string "Hamster" .
The call:
int i; float x; char name[50];
(void) wscanf(L"%2d%f%*d %[0123456789]", &i, &x, name);
with input:
56789 0123 56a72
assigns 56 to i, 789.0 to x, skips 0123, and places the string "56\0" in name. The next call to getchar() shall return
the character 'a' .
APPLICATION USAGE
In format strings containing the '%' form of conversion specifications, each argument in the argument list is used
exactly once.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
getwc(), fwprintf(), setlocale(), wcstod(), wcstol(), wcstoul(), wcrtomb(), the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 7, Locale, <langinfo.h>, <stdio.h>, <wchar.h>
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, Copy-
right (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.open-
group.org/unix/online.html .
IEEE/The Open Group 2003 FWSCANF(3P)
