# c32rtomb

From cppreference.com
< c‎ | string‎ | multibyte

Defined in header `<uchar.h>` |  |
size_t c32rtomb( char* s, char32_t c32, mbstate_t* ps ); |  | (since C11)

Converts a single code point from its variable-length 32-bit wide character representation (but typically, UTF-32) to its narrow multibyte character representation.

If `s` is not a null pointer, the function determines the number of bytes necessary to store the multibyte character representation of `c32` (including any shift sequences), and stores the multibyte character representation in the character array whose first element is pointed to by `s`. At most MB_CUR_MAX bytes can be written by this function.

If `s` is a null pointer, the call is equivalent to c32rtomb(buf, U'\0', ps) for some internal buffer `buf`.

If `c32` is the null wide character U'\0', a null byte is stored, preceded by any shift sequence necessary to restore the initial shift state and the conversion state parameter *ps is updated to represent the initial shift state.

If the macro __STDC_UTF_32__ is defined, the 32-bit encoding used by this function is UTF-32; otherwise, it is implementation-defined. In any case, the multibyte character encoding used by this function is specified by the currently active C locale.

### Parameters

s | - | pointer to narrow character array where the multibyte character will be stored
c32 | - | the 32-bit wide character to convert
ps | - | pointer to the conversion state object used when interpreting the multibyte string

### Return value

On success, returns the number of bytes (including any shift sequences) written to the character array whose first element is pointed to by `s`. This value may be ​0​, e.g. when processing the leading char32_t units in a multi-char32_t-unit sequence (does not occur in UTF-32).

On failure (if c32 is not a valid 32-bit wide character), returns -1, stores EILSEQ in errno, and leaves *ps in unspecified state.

### Example

Run this code

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

    mbstate_t state;
    int main(void)
    {
        setlocale(LC_ALL, "en_US.utf8");
        char32_t in[] = U"zß水🍌"; // or "z\u00df\u6c34\U0001F34C"
        size_t in_sz = sizeof in / sizeof *in;

        printf("Processing %zu UTF-32 code units: [ ", in_sz);
        for(size_t n = 0; n < in_sz; ++n) printf("%#x ", in[n]);
        puts("]");

        char out[MB_CUR_MAX * in_sz];
        char *p = out;
        for(size_t n = 0; n < in_sz; ++n) {
            int rc = c32rtomb(p, in[n], &state);
            if(rc == -1) break;
            p += rc;
        }

        size_t out_sz = p - out;
        printf("into %zu UTF-8 code units: [ ", out_sz);
        for(size_t x = 0; x < out_sz; ++x) printf("%#x ", +(unsigned char)out[x]);
        puts("]");
    }

Output:

    Processing 5 UTF-32 code units: [ 0x7a 0xdf 0x6c34 0x1f34c 0 ]
    into 11 UTF-8 code units: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c 0 ]

### References

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

  - 7.28.1.4 The c32rtomb function (p: 401)

### See also

mbrtoc32 (C11) | generates the next 32-bit wide character from a narrow multibyte string (function)
C++ documentation for c32rtomb

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