mbstowcs, mbstowcs_s

Header: <stdlib.h>

1. Converts a multibyte character string from the array whose first element is pointed to by src to its wide character representation. Converted characters are stored in the successive elements of the array pointed to by dst. No more than len wide characters are written to the destination array.

# Declarations

size_t mbstowcs( wchar_t *dst, const char *src, size_t len)

(until C99)

size_t mbstowcs( wchar_t *restrict dst, const char *restrict src, size_t len)

(since C99)

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

(since C11)

# Parameters

• dst: pointer to wide character array where the wide string will be stored
• src: pointer to the first element of a null-terminated multibyte string to convert
• len: number of wide characters available in the array pointed to by dst
• dstsz: max number of wide characters that will be written (size of the dst array)
• retval: pointer to a size_t object where the result will be stored

# Notes

In most implementations, mbstowcs updates a global static object of type mbstate_t as it processes through the string, and cannot be called simultaneously by two threads, mbsrtowcs should be used in such cases.

POSIX specifies a common extension: if dst is a null pointer, this function returns the number of wide characters that would be written to dst, if converted. Similar behavior is standard for mbstowcs_s and for mbsrtowcs.

# Example

#include <stdio.h>
#include <locale.h>
#include <stdlib.h>
#include <wchar.h>
 
int main(void)
{
    setlocale(LC_ALL, "en_US.utf8");
    const char* mbstr = u8"z\u00df\u6c34\U0001F34C"; // or u8"zß水🍌"
    wchar_t wstr[5];
    mbstowcs(wstr, mbstr, 5);
    wprintf(L"MB string: %s\n", mbstr);
    wprintf(L"Wide string: %ls\n", wstr);
}

# See also

• mbsrtowcsmbsrtowcs_s
• wcstombswcstombs_s
• C++ documentation