vwprintf, vfwprintf, vswprintf, vwprintf_s, vfwprintf_s, vswprintf_s, vsnwprintf_s

Header: <wchar.h>

Loads the data from locations, defined by vlist, converts them to wide string equivalents and writes the results to a variety of sinks.

# Declarations

int vwprintf( const wchar_t* format, va_list vlist );

(since C95) (until C99)

int vwprintf( const wchar_t* restrict format, va_list vlist );

(since C99)

int vfwprintf( FILE* stream, const wchar_t* format, va_list vlist );

(since C95) (until C99)

int vfwprintf( FILE* restrict stream,
const wchar_t* restrict format, va_list vlist );

(since C99)

int vswprintf( wchar_t* buffer, size_t bufsz,
const wchar_t* format, va_list vlist );

(since C95) (until C99)

int vswprintf( wchar_t* restrict buffer, size_t bufsz,
const wchar_t* restrict format, va_list vlist );

(since C99)

int vwprintf_s( const wchar_t* restrict format, va_list vlist);

(since C11)

int vfwprintf_s( FILE* restrict stream,
const wchar_t* restrict format, va_list vlist);

(since C11)

int vswprintf_s( wchar_t* restrict buffer, rsize_t bufsz,
const wchar_t* restrict format, va_list vlist);

(since C11)

int vsnwprintf_s( wchar_t* restrict buffer, rsize_t bufsz,
const wchar_t* restrict format, va_list vlist);

(since C11)

# Parameters

# Notes

All these functions invoke va_arg at least once, the value of arg is indeterminate after the return. These functions to not invoke va_end, and it must be done by the caller.

While narrow strings provide vsnprintf, which makes it possible to determine the required output buffer size, there is no equivalent for wide strings (until C11’s vsnwprintf_s), and in order to determine the buffer size, the program may need to call vswprintf, check the result value, and reallocate a larger buffer, trying again until successful.

vsnwprintf_s, unlike vswprintf_s, will truncate the result to fit within the array pointed to by buffer, even though truncation is treated as an error by most bounds-checked functions.

# Example

#include <locale.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <time.h>
#include <wchar.h>
 
void debug_wlog(const wchar_t* fmt, ...)
{
    struct timespec ts;
    timespec_get(&ts, TIME_UTC);
    char time_buf[100];
    size_t rc = strftime(time_buf, sizeof time_buf, "%D %T", gmtime(&ts.tv_sec));
    snprintf(time_buf + rc, sizeof time_buf - rc, ".%06ld UTC", ts.tv_nsec / 1000);
 
    va_list args;
    va_start(args, fmt);
    wchar_t buf[1024];
    int rc2 = vswprintf(buf, sizeof buf / sizeof *buf, fmt, args);
    va_end(args);
 
    if(rc2 > 0)
       wprintf(L"%s [debug]: %ls\n", time_buf, buf);
    else
       wprintf(L"%s [debug]: (string too long)\n", time_buf);
}
 
int main(void)
{
    setlocale(LC_ALL, "");
    debug_wlog(L"Logging, %d, %d, %d", 1, 2, 3);
}

# See also