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std::c32rtomb(3)	      C++ Standard Libary	      std::c32rtomb(3)

NAME
       std::c32rtomb - std::c32rtomb

Synopsis
	  Defined in header <cuchar>
	  std::size_t  c32rtomb(  char*	s, char32_t c32, std::mbstate_t* ps );
       (since C++11)

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

	  If s is not a	null pointer, the function determines  the  number  of
       bytes necessary to
	  store	 the  multibyte	character representation of c32	(including any
       shift sequences,
	  and taking into account the current multibyte	conversion state *ps),
       and stores the
	  multibyte character representation  in  the  character  array	 whose
       first element is
	  pointed to by	s, updating *ps	as necessary. At most MB_CUR_MAX bytes
       can be written
	  by this function.

	  If s is a null pointer, the call is equivalent to std::c32rtomb(buf,
       U'\0', ps) for
	  some internal	buffer buf.

	  If c32 is the	null wide character U'\0', a null byte is stored, pre-
       ceded by	any
	  shift	 sequence necessary to restore the initial shift state and the
       conversion state
	  parameter *ps	is updated to represent	the initial shift state.

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

Parameters
	  s    - pointer to narrow character array where the multibyte charac-
       ter will	be stored
	  c32 -	the 32-bit character to	convert
	  ps  -	pointer	to the conversion state	object used when  interpreting
       the multibyte
		string

Return value
	  On  success,	returns	 the  number of	bytes (including any shift se-
       quences)	written	to
	  the character	array whose first element is pointed  to  by  s.  This
       value may be
	  0, e.g. when processing the first char32_t in	multi-char32_t-charac-
       ter
	  sequence (does not occur in UTF-32).

	  On  failure  (if  c32	 is not	a valid	32-bit character), returns -1,
       stores EILSEQ in
	  errno, and leaves *ps	in unspecified state.

Example
       // Run this code

	#include <iostream>
	#include <iomanip>
	#include <string_view>
	#include <clocale>
	#include <cuchar>
	#include <climits>

	int main()
	{
	    std::setlocale(LC_ALL, "en_US.utf8");
	    std::u32string_view	strv = U"z"; //	or z\u00df\u6c34\U0001F34C
	    std::cout << "Processing " << strv.size() << " UTF-32 code	units:
       [ ";
	    for(char32_t c : strv)
		std::cout  << std::showbase << std::hex	<< static_cast<int>(c)
       << ' ';
	    std::cout << "]\n";

	    std::mbstate_t state{};
	    char out[MB_LEN_MAX]{};
	    for(char32_t c : strv)
	    {
		std::size_t rc = std::c32rtomb(out, c, &state);
		std::cout << static_cast<int>(c) << " converted	to [ ";
		if(rc != (std::size_t)-1)
		    for(unsigned char c8 : std::string_view{out, rc})
			std::cout << +c8 << ' ';
		std::cout << "]\n";
	    }
	}

Output:
	Processing 4 UTF-32 code units:	[ 0x7a 0xdf 0x6c34 0x1f34c ]
	0x7a converted to [ 0x7a ]
	0xdf converted to [ 0xc3 0x9f ]
	0x6c34 converted to [ 0xe6 0xb0	0xb4 ]
	0x1f34c	converted to [ 0xf0 0x9f 0x8d 0x8c ]

See also
	  mbrtoc32  converts a narrow multibyte	character to UTF-32 encoding
	  (C++11)   (function)
	  do_out    converts a string from internT to externT,	such  as  when
       writing to file
	  [virtual]  (virtual  protected  member  function of std::codecvt<In-
       ternT,ExternT,State>)

http://cppreference.com		  2022.07.31		      std::c32rtomb(3)

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