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

NAME
       std::wcrtomb - std::wcrtomb

Synopsis
	  Defined in header <cwchar>
	  std::size_t wcrtomb( char* s,	wchar_t	wc, std::mbstate_t* ps );

	  Converts a wide 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  wc  (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::wcrtomb(buf,
       L'\0', ps) for
	  some internal	buffer buf.

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

Parameters
	  s  - pointer to narrow character array where the multibyte character
       will be stored
	  wc - the wide	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.

	  On failure (if wc is not a valid wide	character), returns
	  static_cast<std::size_t>(-1),	stores EILSEQ in errno,	and leaves *ps
       in unspecified
	  state.

Example
       // Run this code

	#include <iostream>
	#include <clocale>
	#include <string>
	#include <cwchar>

	void print_wide(const std::wstring& wstr)
	{
	    std::mbstate_t state {};
	    for(wchar_t	wc : wstr) {
		std::string mb(MB_CUR_MAX, '\0');
		std::size_t ret	= std::wcrtomb(&mb[0], wc, &state);
		std::cout  <<  "multibyte  char	 " << mb << " is " << ret << "
       bytes\n";
	    }
	}

	int main()
	{
	    std::setlocale(LC_ALL, "en_US.utf8");
	    std::wstring wstr =	L"z\u00df\u6c34\U0001f34c"; // or L"z"
	    print_wide(wstr);
	}

Output:
	multibyte char z is 1 bytes
	multibyte char	is 2 bytes
	multibyte char	is 3 bytes
	multibyte char	is 4 bytes

See also
	  wctomb    converts a wide character to its multibyte representation
		    (function)
	  mbrtowc   converts the next multibyte	character to  wide  character,
       given state
		    (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::wcrtomb(3)

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