From cppreference.com
< c‎ | string‎ | multibyte
Defined in header <uchar.h>
size_t mbrtoc32( char32_t* pc32, const char* s, size_t n, mbstate_t* ps );
(since C11)

Converts a narrow multibyte character to its 32-bit character representation (typically, UTF-32).

If s is not a null pointer, inspects at most n bytes of the multibyte character string, beginning with the byte pointed to by s to determine the number of bytes necessary to complete the next multibyte character (including any shift sequences). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding 32-bit character and stores it in *pc32 (if pc32 is not null).

If the multibyte character in *s corresponds to a multi-char32_t sequence (not possible with UTF-32), then after the first call to this function, *ps is updated in such a way that the next calls to mbrtoc32 will write out the additional char32_t, without considering *s.

If s is a null pointer, the values of n and pc32 are ignored and the call is equivalent to mbrtoc32(NULL, "", 1, ps).

If the wide character produced is the null character, the conversion state *ps represents 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.


[edit] Parameters

pc32 - pointer to the location where the resulting 32-bit character will be written
s - pointer to the multibyte character string used as input
n - limit on the number of bytes in s that can be examined
ps - pointer to the conversion state object used when interpreting the multibyte string

[edit] Return value

The first of the following that applies:

  • 0 if the character converted from s (and stored in *pc32 if non-null) was the null character
  • the number of bytes [1...n] of the multibyte character successfully converted from s
  • -3 if the next char32_t from a multi-char32_t character has now been written to *pc32. No bytes are processed from the input in this case.
  • -2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc32.
  • -1 if encoding error occurs. Nothing is written to *pc32, the value EILSEQ is stored in errno and the value if *ps is unspecified.

[edit] Example

#include <stdio.h>
#include <locale.h>
#include <string.h>
#include <uchar.h>
#include <assert.h>
mbstate_t state;
int main(void)
    setlocale(LC_ALL, "en_US.utf8");
    char *str = u8"z\u00df\u6c34\U0001F34C"; // or u8"zß水🍌"
    printf("Processing %zu bytes: [ ", strlen(str));
    for(char* p = str; *p; ++p) printf("%#x ", (unsigned char)*p);
    char32_t c32;
    char *ptr = str, *end = str + strlen(str);
    int rc;
    while(rc = mbrtoc32(&c32, ptr, end - ptr, &state))
        printf("Next UTF-32 char: %#x obtained from ", c32);
        assert(rc != -3); // no surrogate pairs in UTF-32
        if(rc > 0) {
            printf("%d bytes [ ", rc);
            for(int n = 0; n < rc; ++n) printf("%#x ", (unsigned char)ptr[n]);
            ptr += rc;


Processing 10 bytes: [ 0x7a 0xc3 0x9f 0xe6 0xb0 0xb4 0xf0 0x9f 0x8d 0x8c ]
Next UTF-32 char: 0x7a obtained from 1 bytes [ 0x7a ]
Next UTF-32 char: 0xdf obtained from 2 bytes [ 0xc3 0x9f ]
Next UTF-32 char: 0x6c34 obtained from 3 bytes [ 0xe6 0xb0 0xb4 ]
Next UTF-32 char: 0x1f34c obtained from 4 bytes [ 0xf0 0x9f 0x8d 0x8c ]

[edit] References

  • C11 standard (ISO/IEC 9899:2011):
  • The mbrtoc32 function (p: 400-401)

[edit] See also

convert a 32-bit wide character to narrow multibyte string
C++ documentation for mbrtoc32