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# wcsrtombs, wcsrtombs_s

From cppreference.com
< c‎ | string‎ | multibyte

Defined in header `<wchar.h>` |  |
size_t wcsrtombs( char *dst, const wchar_t **src, size_t len, mbstate_t* ps ) | (1) | (since C95)
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); | (2) | (since C11)

1) Converts a sequence of wide characters from the array whose first element is pointed to by *src to its narrow multibyte representation that begins in the conversion state described by *ps. If `dst` is not null, converted characters are stored in the successive elements of the char array pointed to by `dst`. No more than `len` bytes are written to the destination array.
Each character is converted as if by a call to wcrtomb. The conversion stops if:
* 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 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==NULL.
2) Same as (1), except that
* 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` 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 `wchar.h`.

### [edit] Parameters

dst | - | pointer to narrow character array where the multibyte characters will be stored
src | - | pointer to pointer to the first element of a null-terminated wide string
len | - | number of bytes available in the array pointed to by dst
ps | - | pointer to the conversion state object
dstsz | - | max number of bytes that will be written (size of the `dst` array)
retval | - | pointer to a size_t object where the result will be stored

### [edit] Return value

1) On success, returns the number of bytes (including any shift sequences, but excluding the terminating '\0') written to the character array whose first element is pointed to by `dst`. If dst==NULL, returns the number of bytes that would have been written. On conversion error (if invalid wide character was encountered), returns (size_t)-1, stores EILSEQ in errno, and leaves *ps in unspecified state.
2) Returns zero on success (in which case the number of bytes excluding terminating zero that were, or would be written to `dst`, is stored in *retval), non-zero on error. In case of a runtime constraint violation, stores (size_t)-1 in *retval (unless `retval` is null) and sets dst[0] to '\0' (unless `dst` is null or `dstmax` is zero or greater than RSIZE_MAX)

### [edit] Example

Run this code

    #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);
        int 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': %d\n", len);
    }

    int main(void)
    {
        setlocale(LC_ALL, "en_US.utf8");
        print_wide(L"z\u00df\u6c34\U0001f34c"); // or L"zß水🍌"
    }

Output:

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

### [edit] References

- 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)

### [edit] See also

wcstombswcstombs_s (C11) | converts a wide string to narrow multibyte character string (function) [edit]
wcrtombwcrtomb_s (C95)(C11) | converts a wide character to its multibyte representation, given state (function) [edit]
mbsrtowcsmbsrtowcs_s (C95)(C11) | converts a narrow multibyte character string to wide string, given state (function) [edit]
C++ documentation for wcsrtombs

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