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fwscanf(3c)
Standard C Library Functions fwscanf(3C)
NAME
fwscanf, wscanf, swscanf, vfwscanf, vwscanf, vswscanf - convert format‐
ted wide-character input
fwscanf_s, wscanf_s, swscanf_s, vfwscanf_s, vwscanf_s, vswscanf_s -
convert formatted wide-character input with additional safety checks
SYNOPSIS
#include <stdio.h>
#include <wchar.h>
int fwscanf(FILE *restrict stream, const wchar_t *restrict format, ...);
int wscanf(const wchar_t *restrict format, ...);
int swscanf(const wchar_t *restrict s,
const wchar_t *restrict format, ...);
#include <stdarg.h>
#include <stdio.h>
#include <wchar.h>
int vfwscanf(FILE *restrict stream, const wchar_t *restrict format,
va_list arg);
int vswcanf(const wchar_t *restrict ws, const wchar_t *restrict format,
va_list arg);
int vwscanf(const wchar_t *restrict format, va_list arg);
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <wchar.h>
int fwscanf_s(FILE *restrict stream,
const wchar_t *restrict format, ...);
int vfwscanf_s(FILE *restrict stream, const wchar_t *restrict format,
va_list arg);
#define __STDC_WANT_LIB_EXT1__ 1
#include <stdarg.h>
#include <wchar.h>
int vswscanf_s(const wchar_t *restrict s, const wchar_t *restrict format,
va_list arg);
int vwscanf_s(const wchar_t *restrict format, va_list arg);
#define __STDC_WANT_LIB_EXT1__ 1
#include <wchar.h>
int wscanf_s(const wchar_t *restrict format, ...);
int swscanf_s(const wchar_t *restrict s,
const wchar_t *restrict format, ...);
DESCRIPTION
The fwscanf() function reads from the named input stream.
The wscanf() function reads from the standard input stream stdin.
The swscanf() function reads from the wide-character string s.
The vfwscanf(), vswscanf(), and vwscanf() functions are similar to the
fwscanf(), swscanf(), and wscanf() functions, respectively, except that
instead of being called with a variable number of arguments, they are
called with an argument list as defined by the <stdarg.h> header. These
functions do not invoke the va_end() macro. Applications using these
functions should call va_end(ap) afterward to clean up.
Each function reads wide-characters, interprets them according to a
format, and stores the results in its arguments. Each expects, as argu‐
ments, 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 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$, but the two forms cannot normally be mixed within a sin‐
gle format wide-character string. The only exception to this is that %%
or %* can be mixed with the %n$ form.
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 program's locale
(category LC_NUMERIC). In the POSIX locale, or in a locale where the
radix character is not defined, the radix character defaults 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 characters); 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 fol‐
lowing appear in sequence:
o An optional assignment-suppressing character *.
o An optional non-zero decimal integer that specifies the max‐
imum field width.
o An option length modifier that specifies the size of the
receiving object.
o A conversion specifier wide-character that specifies the
type of conversion to be applied. The valid conversion wide-
characters are described below.
The fwscanf() functions execute each directive of the format in turn.
If a directive fails, as detailed below, the function returns. 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 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 is 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 fails, and the differing
and subsequent wide-characters remain unread.
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(3C)) are
skipped, unless the conversion specification includes a [, c, or n con‐
version character.
An item is read from the input unless the conversion specification
includes an n conversion wide-character. The length of the item read is
limited to any specified maximum field width. In Solaris default mode,
the input item is defined as the longest sequence of input wide-charac‐
ters that forms a matching sequence. In some cases, fwscanf() might
need to read several extra wide-characters beyond the end of the input
item to find the end of a matching sequence. In C99/SUSv3 mode, the
input item is defined as the longest sequence of input wide-characters
that is, or is a prefix of, a matching sequence. With this definition,
fwscanf() need only read at most one wide-character beyond the end of
the input item. Therefore, in C99/SUSv3 mode, some sequences that are
acceptable to wcstod(3C), wcstol(3C), and similar functions are unac‐
ceptable to fwscanf(). In either mode, fwscanf() attempts to push back
any excess bytes read using ungetc(3C). Assuming all such attempts suc‐
ceed, the first wide-character, if any, after the input item remains
unread. If the length of the input item is 0, the conversion fails.
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 wide-character, the input item
(or, in the case of a %n conversion specification, the count of input
wide-characters) is 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 fails; this condition is a
matching failure. Unless assignment suppression was indicated by a *,
the result of the conversion is 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 intro‐
duced 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 pro‐
vided, the behavior is undefined.
The length modifiers and their meanings are:
hh Specifies that a following d, i, o, u, x, X, or n con‐
version 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 con‐
version 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 con‐
version 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 fol‐
lowing 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 con‐
version 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 con‐
version 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 con‐
version 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 con‐
version 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 wide-characters are valid:
d Matches an optionally signed decimal integer, whose format
is the same as expected for the subject sequence of
wcstol(3C) with the value 10 for the base argument. In the
absence of a size modifier, the corresponding argument must
be a pointer to int.
i Matches an optionally signed integer, whose format is the
same as expected for the subject sequence of wcstol(3C) with
0 for the base argument. In the absence of a size modifier,
the corresponding argument must be a pointer to int.
o Matches an optionally signed octal integer, whose format is
the same as expected for the subject sequence of wcstoul(3C)
with the value 8 for the base argument. In the absence of a
size modifier, the corresponding argument must be a pointer
to unsigned int.
u Matches an optionally signed decimal integer, whose format
is the same as expected for the subject sequence of
wcstoul(3C) with the value 10 for the base argument. In the
absence of a size modifier, the corresponding argument must
be a pointer to unsigned int.
x Matches an optionally signed hexadecimal integer, whose for‐
mat is the same as expected for the subject sequence of
wcstoul(3C) with the value 16 for the base argument. In the
absence of a size modifier, the corresponding argument must
be a pointer to unsigned int.
a,e,f,g Matches an optionally signed floating-point number, whose
format is the same as expected for the subject sequence of
wcstod(3C). In the absence of a size modifier, the corre‐
sponding argument must be a pointer to float. The e, f, and
g specifiers match hexadecimal floating-point values only in
C99/SUSv3 (see standards(7)) mode, but the a specifier
always matches hexadecimal floating-point values.
These conversion specifiers match any subject sequence
accepted by strtod(3C), including the INF, INFINITY, NAN,
and NAN(n-char-sequence) forms. The result of the conversion
is the same as that of calling strtod() (or strtof() or str‐
told()) with the matching sequence, including the raising of
floating-point exceptions and the setting of errno to
ERANGE, if applicable.
s Matches a sequence of non white-space wide-characters. If no
l (ell) qualifier is present, characters from the input
field are converted as if by repeated calls to the wcr‐
tomb(3C) function, with the conversion state described by an
mbstate_t object initialized to zero before the first wide-
character is converted. The corresponding argument must be a
pointer to a character array large enough to accept the
sequence and the terminating null character, which will be
added automatically.
Otherwise, the corresponding argument must be a pointer to
an array of wchar_t large enough to accept the sequence and
the terminating null wide-character, which will 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
are converted as if by repeated calls to the wcrtomb() func‐
tion, with the conversion state described by an mbstate_t
object initialized to zero before the first wide-character
is converted. The corresponding argument must be a pointer
to a character array large enough to accept the sequence and
the terminating null character, which will be added automat‐
ically.
If an l (ell) qualifier is present, the corresponding argu‐
ment must be a pointer to an array of wchar_t large enough
to accept the sequence and the terminating null wide-charac‐
ter, which will be added automatically.
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 con‐
tains 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 minus-sign (−) 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, it indi‐
cates a range of characters to be matched.
c Matches a sequence of wide-characters of the number speci‐
fied by the field width (1 if no field width is present in
the conversion specification). If no l (ell) qualifier is
present, wide-characters from the input field are converted
as if by repeated calls to the wcrtomb() function, with the
conversion state described by an mbstate_t object initial‐
ized to zero before the first wide-character is converted.
The corresponding argument must be a pointer to a character
array large enough to accept the sequence. No null character
is added.
Otherwise, the corresponding argument must be a pointer to
an array of wchar_t large enough to accept the sequence. No
null wide-character is added.
p Matches the set of sequences that is the same as the set of
sequences that is produced by the %p conversion of the cor‐
responding fwprintf(3C) functions. The corresponding argu‐
ment must be a pointer to a pointer to void. If the input
item is a value converted earlier during the same program
execution, the pointer that results will compare equal to
that value; otherwise the behavior of the %p conversion is
undefined.
n No input is consumed. The corresponding argument must be a
pointer to the integer into which is to be written the num‐
ber of wide-characters read from the input so far by this
call to the fwscanf() functions. Execution of a %n conver‐
sion specification does not increment the assignment count
returned at the completion of execution of the function.
C Same as lc.
S Same as ls.
% Matches a single %; no conversion or assignment occurs. The
complete conversion specification must be %%.
If a conversion specification is invalid, the behavior is undefined.
The conversion characters A, E, F, G, and X are also valid and behave
the same as, 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 terminates 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) is terminated with an input failure.
Reaching the end of the string in swscanf() is equivalent to encounter‐
ing end-of-file for fwscanf().
If conversion terminates on a conflicting input, the offending input is
left unread in the input. Any trailing white space (including newline)
is left unread unless matched by a conversion specification. The suc‐
cess of literal 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 will be
marked for update by the first successful execution of fgetc(3C),
fgetwc(3C), fgets(3C), fgetws(3C), fread(3C), getc(3C), getwc(3C),
getchar(3C), getwchar(3C), gets(3C), fscanf(3C) or fwscanf() using
stream that returns data not supplied by a prior call to ungetc(3C).
C11 Bounds Checking Interfaces
The fwscanf_s(), wscanf_s(), swscanf_s(), vwscanf_s(), vfwscanf_s(),
and vswscanf_s() functions are part of the C11 bounds checking inter‐
faces specified in the C11 standard, Annex K. They are similar to their
respective non-bounds checking interfaces, except for providing addi‐
tional checks on the parameters passed and explicit runtime-constraints
as defined in the C11 standard. See runtime_constraint_handler(3C) and
INCITS/ISO/IEC 9899:2011.
RETURN VALUES
Upon successful completion, these functions return the number of suc‐
cessfully matched and assigned input items; this number can be 0 in the
event of an early matching failure. If the input ends before the first
matching failure or conversion, or in the case of the bounds checking
interfaces, a runtime-constraint violation is detected, EOF is
returned. If a read error occurs, the error indicator for the stream is
set, EOF is returned, and errno is set to indicate the error.
ERRORS
For the conditions under which the fwscanf() functions will fail and
may fail, refer to fgetwc(3C).
In addition, fwscanf() may fail if:
EILSEQ Input byte sequence does not form a valid character.
EINVAL There are insufficient arguments.
USAGE
In format strings containing the % form of conversion specifications,
each argument in the argument list is used exactly once.
EXAMPLES
Example 1 wscanf() example
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
will assign to n the value 3, to i the value 25, to x the value 5.432,
and name will contain 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
will assign 56 to i, 789.0 to x, skip 0123, and place the string 56\0
in name. The next call to getchar(3C) will return the character a.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSee below _
StandardSee standards(7).
The fwscanf(), wscanf(), swscanf(), vfwscanf(), vwscanf(), and vsws‐
canf() functions can be used safely in multithreaded applications.
The fwscanf_s(), wscanf_s(), swscanf_s(), vfwscanf_s(), vwscanf_s(),
and vswscanf_s() functions cannot be used safely in a multithreaded
application due to the runtime constraint handler. For more informa‐
tion, see the runtime_constraint_handler(3C) man page.
SEE ALSO
fgetc(3C), fgets(3C), fgetwc(3C), fgetws(3C), fread(3C), fscanf(3C),
fwprintf(3C), getc(3C), getchar(3C), gets(3C), getwc(3C), getwchar(3C),
setlocale(3C), strtod(3C), wcrtomb(3C), wcstod(3C), wcstol(3C),
wcstoul(3C), attributes(7), standards(7), runtime_constraint_han‐
dler(3C)
NOTES
The behavior of the conversion specifier "%%" has changed for all of
the functions described on this manual page. Previously the "%%" speci‐
fier accepted a "%" character from input only if there were no preced‐
ing whitespace characters. The new behavior accepts "%" even if there
are preceding whitespace characters. This new behavior now aligns with
the description on this manual page and in various standards. If the
old behavior is desired, the conversion specification "%*[%]" can be
used.
Oracle Solaris 11.4 11 May 2021 fwscanf(3C)