From cppreference.com
std::size_tmbrtoc32(char32_t*pc32,constchar*s,std::size_tn,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(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
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
is stored in
and the value of *ps is unspecified.
Examples
Run this code
#include<cassert>#include<clocale>#include<cstring>#include<cuchar>#include<cwchar>#include<iomanip>#include<iostream>intmain(){std::setlocale(LC_ALL,"en_US.utf8");std::stringstr="z\u00df\u6c34\U0001F34C";// or u8"zß水🍌"std::cout<<"Processing "<<str.size()<<" bytes: [ "<<std::showbase;for(unsignedcharc:str)std::cout<<std::hex<<+c<<' ';std::cout<<"]\n";std::mbstate_tstate{};// zero-initialized to initial statechar32_tc32;constchar*ptr=str.c_str(),*end=str.c_str()+str.size()+1;while(std::size_trc=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-32if(rc==(std::size_t)-1)break;if(rc==(std::size_t)-2)break;std::cout<<std::dec<<rc<<" bytes [ ";for(std::size_tn=0;n<rc;++n)std::cout<<std::hex<<+static_cast<unsignedchar>(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
(C++11)
converts a UTF-32 character to narrow multibyte encoding
(function)
[virtual]
converts a string from ExternT to InternT, such as when reading from file
(virtual protected member function of std::codecvt<InternT,ExternT,StateT>)