mbrtoc32
<uchar.h>
size_t n, mbstate_t * restrict ps );
Converts a single code point from its narrow multibyte character representation to its variable-length 32-bit wide character representation (but 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, and taking into account the current multibyte conversion state *ps). If the function determines that the next multibyte character in s is complete and valid, converts it to the corresponding 32-bit wide 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. The macro is always defined and the encoding is always UTF-32.(since C23) In any case, the multibyte character encoding used by this function is specified by the currently active C locale.
[edit] Parameters
[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. - (size_t )-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.
- (size_t )-2 if the next n bytes constitute an incomplete, but so far valid, multibyte character. Nothing is written to *pc32.
- (size_t )-1 if encoding error occurs. Nothing is written to *pc32, the value EILSEQ is stored in errno and the value of *ps is unspecified.
[edit] Example
On MSVC you will need the /utf-8 compiler flag for UTF_8 to work properly.
#include <assert.h> #include <locale.h> #include <stdio.h> #include <uchar.h> int main(void) { setlocale (LC_ALL, "en_US.utf8"); char in[] = u8"zß水🍌"; // or "z\u00df\u6c34\U0001F34C" enum { in_size = sizeof in / sizeof *in }; printf ("Processing %d UTF-8 code units: [", in_size); for (int i = 0; i < in_size; ++i) printf ("%s%02X", i ? " " : "", (unsigned char)in[i]); puts ("]"); char32_t out[in_size]; char32_t* p_out = out; char* p_in = in; char* end = in + in_size; mbstate_t state = {0}; size_t rc; while ((rc = mbrtoc32(p_out, p_in, end - p_in, &state))) { assert (rc != (size_t )-3); // no surrogate pairs in UTF-32 if (rc == (size_t )-1) break; // invalid input if (rc == (size_t )-2) break; // truncated input p_in += rc; ++p_out; } size_t out_size = p_out+1 - out; printf ("into %zu UTF-32 code units: [", out_size); for (size_t i = 0; i < out_size; ++i) printf ("%s%08X", i ? " " : "", out[i]); puts ("]"); }
Output:
Processing 11 UTF-8 code units: [7A C3 9F E6 B0 B4 F0 9F 8D 8C 00] into 5 UTF-32 code units: [0000007A 000000DF 00006C34 0001F34C 00000000]
[edit] References
- C23 standard (ISO/IEC 9899:2024):
- 7.30.1.5 The mbrtoc32 function (p: 410)
- C17 standard (ISO/IEC 9899:2018):
- 7.28.1.3 The mbrtoc32 function (p: 293-294)
- C11 standard (ISO/IEC 9899:2011):
- 7.28.1.3 The mbrtoc32 function (p: 400-401)