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FWSCANF(3P) POSIX Programmer's Manual FWSCANF(3P)
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.
fwscanf, swscanf, wscanf — convert formatted wide-character input
#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, ...);
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 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 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
directives. 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
character 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
receiving 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
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 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.
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(3p))
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 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 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 %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 corresponding 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
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. If the 'm' assignment-allocation character is
specified, the conversion 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 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 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 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 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
terminating 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)
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. 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-
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
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
characters 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 <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 character, 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. No null character is added. If the
'm' assignment-allocation character is not specified, the
application 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 character is specified, the application
shall ensure that the corresponding 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() functions. 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 consumed. 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
assignment 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
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.
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 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(), vfwscanf(), vwscanf(), or wscanf() using stream that
returns data not supplied by a prior call to ungetwc().
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.
For the conditions under which the fwscanf() functions shall fail and
may fail, refer to fgetwc(3p).
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.
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'.
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.
None.
None.
Section 2.5, Standard I/O Streams, getwc(3p), fwprintf(3p),
setlocale(3p), wcstod(3p), wcstol(3p), wcstoul(3p), wcrtomb(3p)
The Base Definitions volume of POSIX.1‐2008, Chapter 7, Locale,
stdio.h(0p), wchar.h(0p)
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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FWSCANF(3P)
Pages that refer to this page: wchar.h(0p), fwprintf(3p), swscanf(3p), vfwscanf(3p), wscanf(3p)