WPRINTF(3) Linux Programmer’s Manual WPRINTF(3)
wprintf, fwprintf, swprintf, vwprintf, vfwprintf, vswprintf - formatted
wide character output conversion
#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);
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 over‐
flow 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 con‐
verted 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 writ‐
ten up to (but not including) the terminating null wide charac‐
ter. 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 termi‐
nating 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 char‐
acter. 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.
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.
C99.
fprintf(3), fputwc(3), fwide(3), printf(3), snprintf(3).
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 plat‐
form 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 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()).
GNU 1999-11-20 WPRINTF(3)