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std::mbrtoc32(3)	       C++ Standard Libary		std::mbrtoc32(3)

NAME
     std::mbrtoc32 - std::mbrtoc32

Synopsis
	Defined in header <cuchar>
	std::size_t mbrtoc32( char32_t* pc32,

			      const char* s,	     (since C++11)
			      std::size_t n,

			      std::mbstate_t* ps );

	Converts  a narrow multibyte character to its UTF-32 character represen-
     tation.

	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 se-
     quence (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 cur-
     rently 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 of *ps is unspecified.

Examples
     // Run this code

      #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"zAae<degree>'dh"

	  std::cout << "Processing " << str.size() << " bytes: [ " << std::show-
     base;
	  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;
	  }
      }

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  convert a 32-bit wide character to narrow multibyte string
	(C++11)   (function)
	do_in	   converts a string from ExternT to InternT, such as when read-
     ing from file
	[virtual] (virtual protected member function of
		  std::codecvt<InternT,ExternT,StateT>)
	C documentation for
	mbrtoc32

http://cppreference.com 	   2024.06.10			std::mbrtoc32(3)
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