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 (consult 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 functionality described on this reference page is aligned with the
ISO C standard. Any conflict between the requirements described here
and the ISO C standard is unintentional. This volume of POSIX.1‐2008
defers to the ISO C standard.
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 num‐
bered 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 spec‐
ifications 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 lan‐
guage-dependent radix character in the input string, encoded as a wide-
character value. The radix character is defined in the current 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 direc‐
tives. Each directive is composed of one of the following: one or more
white-space wide characters (<space>, <tab>, <newline>, <vertical-tab>,
or <form-feed>); an ordinary wide character (neither '%' nor a white-
space character); or a conversion specification.
Each conversion specification is introduced by the '%' or by the char‐
acter 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 assignment-allocation character 'm'.
* An optional length modifier that specifies the size of the receiv‐
ing object.
* A conversion specifier wide character that specifies the type of
conversion to be applied. The valid conversion specifiers 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 unavail‐
ability of input bytes) or matching failures (due to inappropriate
input).
A directive composed of one or more white-space wide characters is exe‐
cuted 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 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 charac‐
ter from being read, the directive shall fail.
A directive that is a conversion specification defines a set of match‐
ing input sequences, as described below for each conversion wide char‐
acter. 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 con‐
version specifier.
An item shall be read from the input, unless the conversion specifica‐
tion includes an n 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.
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 exe‐
cution 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-char‐
acter 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 %c, %s, and %[ conversion specifiers shall accept an optional
assignment-allocation character 'm', which shall cause a memory buffer
to be allocated to hold the wide-character string converted including a
terminating null wide character. In such a case, the argument corre‐
sponding to the conversion specifier should be a reference to a pointer
value that will receive a pointer to the allocated buffer. The system
shall allocate a buffer as if malloc() had been called. The application
shall be responsible for freeing the memory after usage. If there is
insufficient memory to allocate a buffer, the function shall set errno
to [ENOMEM] and a conversion error shall result. If the function
returns EOF, any memory successfully allocated for parameters using
assignment-allocation character 'm' by this call shall be freed before
the function returns.
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 con‐
version 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. If the
'm' assignment-allocation character is specified, the conver‐
sion applies to an argument with the type pointer to a 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 dou‐
ble.
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 applica‐
tion shall ensure that the corresponding 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 modi‐
fier, the application shall ensure that the corresponding argu‐
ment 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 corre‐
sponding 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 corresponding 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. If the 'm' assignment-allocation character is not
specified, 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 a
pointer to a wchar_t.
If the l (ell) qualifier is present and the 'm' assignment-
allocation character is not specified, 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 termi‐
nating null wide character, which shall be added automatically.
If the l (ell) qualifier is present and the 'm' assignment-
allocation character is present, the application shall ensure
that the corresponding argument is a pointer to a pointer to a
wchar_t.
[ Matches a non-empty sequence of wide characters from a set of
expected wide characters (the scanset). If no l (ell) quali‐
fier 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 ini‐
tialized to zero before the first wide character is converted.
If the 'm' assignment-allocation character is not specified,
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 a pointer to a
wchar_t.
If an l (ell) qualifier is present and the 'm' assignment-allo‐
cation character is not specified, 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. If an l (ell) qualifier is present and
the 'm' assignment-allocation character is specified, the
application shall ensure that the corresponding argument is a
pointer to a pointer to a wchar_t.
The conversion specification includes all subsequent wide char‐
acters in the format string up to and including the matching
<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 <circum‐
flex> ('^'), in which case the scanset contains all wide char‐
acters that do not appear in the scanlist between the <circum‐
flex> and the <right-square-bracket>. If the conversion speci‐
fication 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 character, nor the sec‐
ond 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. No null character is added. If the 'm'
assignment-allocation character is not specified, the applica‐
tion shall ensure that the corresponding argument is a pointer
to the initial element of a character array large enough to
accept the sequence. Otherwise, the application shall ensure
that the corresponding argument is a pointer to a pointer to a
char.
No null wide character is added. If an l (ell) length modifier
is present and the 'm' assignment-allocation character is not
specified, the application shall ensure that the corresponding
argument shall be a pointer to the initial element of an array
of wchar_t large enough to accept the sequence. If an l (ell)
qualifier is present and the 'm' assignment-allocation charac‐
ter is specified, the application shall ensure that the corre‐
sponding argument is a pointer to a pointer to a wchar_t.
p Matches an implementation-defined set of sequences, which shall
be the same as the set of sequences that is produced by the %p
conversion specification of the corresponding fwprintf() func‐
tions. The application shall ensure that the corresponding
argument is a pointer to a pointer to void. 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 %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 con‐
sumed. If the conversion specification includes an assignment-
suppressing wide character or a field width, the behavior is
undefined.
C Equivalent to lc.
S Equivalent to ls.
% Matches a single '%' wide character; no conversion or assign‐
ment shall occur. The complete conversion specification 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 permitted), execution of the current conver‐
sion 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 specifi‐
cation (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 specifi‐
cation. The success of literal matches and suppressed assignments is
only directly determinable via the %n conversion specification.
The fwscanf() and wscanf() functions may mark the last data access
timestamp of the file associated with stream for update. The last data
access timestamp shall be marked for update by the first successful
execution of fgetwc(), fgetws(), fwscanf(), getwc(), getwchar(), vfws‐
canf(), vwscanf(), or wscanf() using stream that returns data not sup‐
plied by a prior call to ungetwc().
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 any
error occurs, EOF shall be returned, and errno shall be set to indicate
the error. If a read error occurs, the error indicator for the stream
shall be set.
ERRORS
For the conditions under which the fwscanf() functions shall fail and
may fail, refer to fgetwc().
In addition, the fwscanf() function shall fail if:
EILSEQ Input byte sequence does not form a valid character.
ENOMEM Insufficient storage space is available.
In addition, the fwscanf() function may fail if:
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.
For functions that allocate memory as if by malloc(), the application
should release such memory when it is no longer required by a call to
free(). For fwscanf(), this is memory allocated via use of the 'm'
assignment-allocation character.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.5, Standard I/O Streams, getwc(), fwprintf(), setlocale(),
wcstod(), wcstol(), wcstoul(), wcrtomb()
The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale,
<stdio.h>, <wchar.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FWSCANF(3P)
