wcsrtombs, wcsrtombs_s

size_t wcsrtombs( char *dst, const wchar_t **src, size_t len, mbstate_t* ps );

size_t wcsrtombs( char *restrict dst, const wchar_t **restrict src, size_t len,
                  mbstate_t *restrict ps );

errno_t wcsrtombs_s( size_t *restrict retval, char *restrict dst, rsize_t dstsz,
                     const wchar_t **restrict src, rsize_t len,
                     mbstate_t *restrict ps );

• The null character L'\0' was converted and stored. The bytes stored in this case are the unshift sequence (if necessary) followed by '\0', *src is set to null pointer value and *ps represents the initial shift state.
• A wchar_t was found that does not correspond to a valid character in the current C locale. *src is set to point at the first unconverted wide character.
• the next multibyte character to be stored would exceed len. *src is set to point at the first unconverted wide character. This condition is not checked if dst is a null pointer.

• the function returns its result as an out-parameter retval
• if the conversion stops without writing a null character, the function will store '\0' in the next byte in dst, which may be dst[len] or dst[dstsz], whichever comes first (meaning up to len+1/dstsz+1 total bytes may be written). In this case, there may be no unshift sequence written before the terminating null.
• the function clobbers the destination array from the terminating null and until dstsz
• If src and dst overlap, the behavior is unspecified.
• the following errors are detected at runtime and call the currently installed constraint handler function:

• retval, ps, src, or *src is a null pointer
• dstsz or len is greater than RSIZE_MAX (unless dst is null)
• dstsz is not zero (unless dst is null)
• len is greater than dstsz and the conversion does not encounter null or encoding error in the src array by the time dstsz is reached (unless dst is null)

As with all bounds-checked functions, wcsrtombs_s only guaranteed to be available if __STDC_LIB_EXT1__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT1__ to the integer constant 1 before including <wchar.h>.

Parameters

Return value

Example

#include <stdio.h>
#include <locale.h>
#include <string.h>
#include <wchar.h>
 
void print_wide(const wchar_t* wstr)
{
    mbstate_t state;
    memset(&state, 0, sizeof state);
    size_t len = 1 + wcsrtombs(NULL, &wstr, 0, &state);
    char mbstr[len];
    wcsrtombs(mbstr, &wstr, len, &state);
    printf("Multibyte string: %s\n", mbstr);
    printf("Length, including '\\0': %zu\n", len);
}
 
int main(void)
{
    setlocale(LC_ALL, "en_US.utf8");
    print_wide(L"z\u00df\u6c34\U0001f34c"); // or L"zß水🍌"
}

Multibyte string: zß水🍌
Length, including '\0': 11

References

• C17 standard (ISO/IEC 9899:2018):
• 7.29.6.4.2 The wcsrtombs function (p: 324-325)
• K.3.9.3.2.2 The wcsrtombs_s function (p: 471-472)
• C11 standard (ISO/IEC 9899:2011):
• 7.29.6.4.2 The wcsrtombs function (p: 446)
• K.3.9.3.2.2 The wcsrtombs_s function (p: 649-651)
• C99 standard (ISO/IEC 9899:1999):
• 7.24.6.4.2 The wcsrtombs function (p: 392)

See also