std:: mbrtoc32

Converts a narrow multibyte character to its UTF-32 character representation.

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 std :: mbrtoc32 ( nullptr, "" , 1 , ps ) .

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

The multibyte encoding used by this function is specified by the currently active C locale.

Parameters

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 of * ps is unspecified.

Examples

#include <cassert>
#include <clocale>
#include <cstring>
#include <cuchar>
#include <cwchar>
#include <iomanip>
#include <iostream>
 
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
 
    std::string str = "z\u00df\u6c34\U0001F34C"; // or u8"zß水🍌"
 
    std::cout << "Processing " << str.size() << " bytes: [ " << std::showbase;
    for (unsigned char c : str)
        std::cout << std::hex << +c << ' ';
    std::cout << "]\n";
 
    std::mbstate_t state{}; // zero-initialized to initial state
    char32_t c32;
    const char* ptr = str.c_str(), *end = str.c_str() + str.size() + 1;
 
    while (std::size_t rc = std::mbrtoc32(&c32, ptr, end - ptr, &state))
    {
        std::cout << "Next UTF-32 char: " << std::hex
                  << static_cast<int>(c32) << " obtained from ";
        assert(rc != (std::size_t) - 3); // no surrogates in UTF-32
        if (rc == (std::size_t) - 1)
            break;
        if (rc == (std::size_t) - 2)
            break;
        std::cout << std::dec << rc << " bytes [ ";
        for (std::size_t n = 0; n < rc; ++n)
            std::cout << std::hex << +static_cast<unsigned char>(ptr[n]) << ' ';
        std::cout << "]\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 ]

See also