fwprintf(3) -- Linux man page

 

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, ...);

#include <stdarg.h>

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);
 

DESCRIPTION

The wprintf family of functions is the wide-character equivalent of the printf 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 function fwide for more information.

The fwprintf and vfwprintf functions perform wide character output to stream. stream must not be byte oriented; see function fwide 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, vprintf, fprintf, vfprintf, sprintf, vsprintf 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 and vsprintf do not. (snprintf and vsnprintf 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 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 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. 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, 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.  

CONFORMING TO

ISO/ANSI C, UNIX98  

SEE ALSO

printf(3), fprintf(3), snprintf(3), fputwc(3), fwide(3), wscanf(3)  

NOTES

The behaviour 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 only work correctly 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 GNU libc represents wide characters using their Unicode (ISO-10646) code point, but other platforms don't do this. Also, the use of ISO 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 or iconv, followed by mbstowcs).