fwprintf(3)
NAME
wprintf, fwprintf, swprintf, vwprintf, vfwprintf, vswprintf - formatted
wide-character output conversion
SYNOPSIS
#include <stdio.h>
#include <wchar.h>
int wprintf(const wchar_t *format, ...);
int fwprintf(FILE *stream, const wchar_t *format, ...);
int swprintf(wchar_t *wcs, size_t maxlen,
const wchar_t *format, ...);
int vwprintf(const wchar_t *format, va_list args);
int vfwprintf(FILE *stream, const wchar_t *format, va_list args);
int vswprintf(wchar_t *wcs, size_t maxlen,
const wchar_t *format, va_list args);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
All functions shown above:
_XOPEN_SOURCE >= 500 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L
DESCRIPTION
The wprintf() family of functions is the wide-character equivalent of
the printf(3) family of functions. It performs formatted output of
wide characters.
The wprintf() and vwprintf() functions perform wide-character output to
stdout. stdout must not be byte oriented; see fwide(3) for more
information.
The fwprintf() and vfwprintf() functions perform wide-character output
to stream. stream must not be byte oriented; see fwide(3) for more
information.
The swprintf() and vswprintf() functions perform wide-character output
to an array of wide characters. The programmer must ensure that there
is room for at least maxlen wide characters at wcs.
These functions are like the printf(3), vprintf(3), fprintf(3),
vfprintf(3), sprintf(3), vsprintf(3) functions except for the following
differences:
* The format string is a wide-character string.
* The output consists of wide characters, not bytes.
* swprintf() and vswprintf() take a maxlen argument, sprintf(3)
and vsprintf(3) do not. (snprintf(3) and vsnprintf(3) take a
maxlen argument, but these functions do not return -1 upon
buffer overflow on Linux.)
The treatment of the conversion characters c and s is different:
c If no l modifier is present, the int argument is converted to a
wide character by a call to the btowc(3) function, and the
resulting wide character is written. If an l modifier is
present, the wint_t (wide character) argument is written.
s If no l modifier is present: the const char * argument is
expected to be a pointer to an array of character type (pointer
to a string) containing a multibyte character sequence beginning
in the initial shift state. Characters from the array are
converted to wide characters (each by a call to the mbrtowc(3)
function with a conversion state starting in the initial state
before the first byte). The resulting wide characters are
written up to (but not including) the terminating null wide
character (L'\0'). If a precision is specified, no more wide
characters than the number specified are written. Note that the
precision determines the number of wide characters written, not
the number of bytes or screen positions. The array must contain
a terminating null byte ('\0'), unless a precision is given and
it is so small that the number of converted wide characters
reaches it before the end of the array is reached. If an l
modifier is present: the const wchar_t * argument is expected to
be a pointer to an array of wide characters. Wide characters
from the array are written up to (but not including) a
terminating null wide character. If a precision is specified,
no more than the number specified are written. The array must
contain a terminating null wide character, unless a precision is
given and it is smaller than or equal to the number of wide
characters in the array.
RETURN VALUE
The functions return the number of wide characters written, excluding
the terminating null wide character in case of the functions swprintf()
and vswprintf(). They return -1 when an error occurs.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
Interface Attribute Value
wprintf(), fwprintf(), Thread safety MT-Safe locale
swprintf(), vwprintf(),
vfwprintf(), vswprintf()
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C99.
NOTES
The behavior of wprintf() et al. depends on the LC_CTYPE category of
the current locale.
If the format string contains non-ASCII wide characters, the program
will work correctly only if the LC_CTYPE category of the current locale
at run time is the same as the LC_CTYPE category of the current locale
at compile time. This is because the wchar_t representation is
platform- and locale-dependent. (The glibc represents wide characters
using their Unicode (ISO-10646) code point, but other platforms don't
do this. Also, the use of C99 universal character names of the form
\unnnn does not solve this problem.) Therefore, in internationalized
programs, the format string should consist of ASCII wide characters
only, or should be constructed at run time in an internationalized way
(e.g., using gettext(3) or iconv(3), followed by mbstowcs(3)).
SEE ALSO
fprintf(3), fputwc(3), fwide(3), printf(3), snprintf(3)
COLOPHON
This page is part of release 4.09 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
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