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# wctomb, wctomb_s

From cppreference.com
< c‎ | string‎ | multibyte

Defined in header `<stdlib.h>` |  |
int wctomb( char *s, wchar_t wc ); | (1) |
errno_t wctomb_s(int *restrict status, char *restrict s, rsize_t ssz, wchar_t wc); | (2) | (since C11)

1) Converts a wide character `wc` to multibyte encoding and stores it (including any shift sequences) in the char array whose first element is pointed to by `s`. No more than MB_CUR_MAX characters are stored.
If `wc` is the null character, the null byte is written to `s`, preceded by any shift sequences necessary to restore the initial shift state.
If `s` is a null pointer, this function resets the global conversion state and determines whether shift sequences are used.
2) Same as (1), except that the result is returned in the out-parameter `status` and the following errors are detected at runtime and call the currently installed constraint handler function:

  - `ssz` is less than the number of bytes that would be written (unless `s` is null)
  - `ssz` is greater than RSIZE_MAX (unless `s` is null)
  - `s` is a null pointer but `ssz` is not zero
  As all bounds-checked functions, `wctomb_s` is 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 `stdlib.h`.

### [edit] Notes

Each call to `wctomb` updates the internal global conversion state (a static object of type mbstate_t, only known to this function). If the multibyte encoding uses shift states, this function is not reentrant. In any case, multiple threads should not call `wctomb` without synchronization: wcrtomb or `wctomb_s` may be used instead.

Unlike most bounds-checked functions, `wctomb_s` does not null-terminate its output, because it is designed to be used in loops that process strings character-by-character.

### [edit] Parameters

s | - | pointer to the character array for output
wc | - | wide character to convert
ssz | - | maximum number of bytes to write to `s` (size of the array `s`)
status | - | pointer to an out-parameter where the result (length of the multibyte sequence or the shift sequence status) will be stored

### [edit] Return value

1) If `s` is not a null pointer, returns the number of bytes that are contained in the multibyte representation of `wc` or -1 if `wc` is not a valid character.
If `s` is a null pointer, resets its internal conversion state to represent the initial shift state and returns ​0​ if the current multibyte encoding is not state-dependent (does not use shift sequences) or a non-zero value if the current multibyte encoding is state-dependent (uses shift sequences).
2) zero on success, in which case the multibyte representation of `wc` is stored in `s` and its length is stored in *status, or, if `s` is null, the shift sequence status is stored in `status`). Non-zero on encoding error or runtime constraint violation, in which case (size_t)-1 is stored in *status. The value stored in *status never exceeds MB_CUR_MAX

### [edit] Example

Run this code

    #include <stdio.h>
    #include <stdlib.h>
    #include <locale.h>

    void demo(wchar_t wc)
    {
        printf("State-dependent encoding?   %d\n", wctomb(NULL, wc));

        char mb[MB_CUR_MAX];
        int len = wctomb(mb,wc);
        printf("wide char '%lc' -> multibyte char '", wc);
        for (int idx = 0; idx < len; ++idx)
            printf("%#2x ", (unsigned char)mb[idx]);
        printf("'\n");
    }

    int main(void)
    {
        setlocale(LC_ALL, "en_US.utf8");
        printf("MB_CUR_MAX = %zu\n", MB_CUR_MAX);
        demo(L'A');
        demo(L'\u00df');
        demo(L'\U0001d10b');
    }

Possible output:

    MB_CUR_MAX = 6
    State-dependent encoding?   0
    wide char 'A' -> multibyte char '0x41 '
    State-dependent encoding?   0
    wide char 'ß' -> multibyte char '0xc3 0x9f '
    State-dependent encoding?   0
    wide char '𝄋' -> multibyte char '0xf0 0x9d 0x84 0x8b '

### [edit] References

- C11 standard (ISO/IEC 9899:2011):

  - 7.22.7.3 The wctomb function (p: 358-359)

  - K.3.6.4.1 The wctomb_s function (p: 610-611)

- C99 standard (ISO/IEC 9899:1999):

  - 7.20.7.3 The wctomb function (p: 322-323)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.10.7.3 The wctomb function

### [edit] See also

mbtowc | converts the next multibyte character to wide character (function) [edit]
wcrtombwcrtomb_s (C95)(C11) | converts a wide character to its multibyte representation, given state (function) [edit]
C++ documentation for wctomb

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