Tribblix: manual page: fwscanf.3c

FWSCANF(3C) Standard C Library Functions FWSCANF(3C)

NAME

fwscanf, wscanf, swscanf, vfwscanf, vwscanf, vswscanf - convert
formatted wide-character input

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);

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 equivalent 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) afterwards
to clean up.

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 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.

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
defaults 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 characters); an ordinary wide-character (neither %
nor a white-space character); or a conversion specification. Each
conversion specification is introduced by a % or the sequence %n$
after which the following appear in sequence:

o An optional assignment-suppressing character *.

o An optional non-zero decimal integer that specifies the
maximum 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
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 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
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(3C)) are
skipped, unless the conversion specification includes a [, c, or n
conversion 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-characters 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 unacceptable to fwscanf(). In
either mode, fwscanf() attempts to push back any excess bytes read
using ungetc(3C). Assuming all such attempts succeed, 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
execution 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
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 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
format 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
corresponding 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 strtold()) 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
wcrtomb(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()
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.

If an l (ell) qualifier is present, 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.

The conversion specification includes all subsequent widw
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 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 indicates a range of characters to
be matched.

c
Matches a sequence of wide-characters of the number
specified 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 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. 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
corresponding fwprintf(3C) functions. The corresponding
argument 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
number of wide-characters read from the input so far by
this call to the fwscanf() functions. Execution of a %n
conversion 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
conversion 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
encountering 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 success 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).

RETURN VALUES

Upon successful completion, these functions return the number of
successfully 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, 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

NOTES

The behavior of the conversion specifier "%%" has changed for all of
the functions described on this manual page. Previously the "%%"
specifier accepted a "%" character from input only if there were no
preceding 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.

February 17, 2023 FWSCANF(3C)