std::mbrtoc32

 

C++

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Technical Specifications

 

Strings library

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Classes

basic_string

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Null-terminated multibyte strings

Wide/multibyte conversions
mbsinit
mbtowc mbstowcs btowc mbrtowc mbsrtowcs mbrtoc16 (C++11) mbrtoc32 (C++11) mblen	wctomb wcstombs wctob wcrtomb wcsrtombs c16rtomb (C++11) c32rtomb (C++11) mbrlen
Types
mbstate_t

 

Defined in header <cuchar>
std::size_t mbrtoc32( char32_t* pc32,                       const char* s,                       std::size_t n,                       std::mbstate_t* ps );		(since C++11)

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(NULL, "", 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

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

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.

Examples

Run this code

#include <iostream>
#include <iomanip>
#include <clocale>
#include <cstring>
#include <cwchar>
#include <cuchar>
#include <cassert>
 
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
 
    std::string str = u8"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[0], *end = &str[0] + str.size();
 
    while(int rc = std::mbrtoc32(&c32, ptr, end - ptr, &state))
    {   
        std::cout << "Next UTF-32 char: " << std::hex << c32 << " obtained from ";
        assert(rc != -3); // no surrogates in UTF-32
        if(rc > 0) {
            std::cout << std::dec << rc << " bytes [ ";
            for(int n = 0; n < rc; ++n)
                std::cout << std::hex << +(unsigned char)ptr[n] << ' ';
            std::cout << "]\n";
            ptr += rc;
        }
    }
}

Output:

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

c32rtomb (C++11)	convert a 32-bit wide character to narrow multibyte string (function)
do_in [virtual]	converts a string from externT to internT, such as when reading from file (virtual protected member function of std::codecvt)
C documentation for mbrtoc32