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

NAME
     std::codecvt_mode - std::codecvt_mode

Synopsis
	Defined in header <codecvt>
	enum codecvt_mode {

	    consume_header = 4,      (since C++11)
	    generate_header = 2,     (deprecated in C++17)
	    little_endian = 1	     (removed in C++26)

	};

	The	 facets      std::codecvt_utf8,      std::codecvt_utf16,     and
     std::codecvt_utf8_utf16 accept
	an optional value of type  std::codecvt_mode  as  a  template  argument,
     which specifies
	optional features of the unicode string conversion.

Constants
	Defined in header <locale>
	Value		Meaning
	little_endian	assume the input is in little-endian byte order (applies
     to UTF-16
			input only, the default is big-endian)
			consume  the byte order mark, if present at the start of
     input
	consume_header	sequence, and (in case of UTF-16), rely on the byte  or-
     der it
			specifies for decoding the rest of the input
	generate_header  output  the  byte order mark at the start of the output
     sequence

	The recognized byte order marks are:

	0xfe 0xff      UTF-16 big-endian
	0xff 0xfe      UTF-16 little-endian
	0xef 0xbb 0xbf UTF-8 (no effect on endianness)

	If std::consume_header is not selected when  reading  a  file  beginning
     with byte order
	mark,  the Unicode character U+FEFF (Zero width non-breaking space) will
     be read as
	the first character of the string content.

Example
	The following example demonstrates consuming the UTF-8 BOM:

     // Run this code

      #include <codecvt>
      #include <cwchar>
      #include <fstream>
      #include <iostream>
      #include <locale>
      #include <string>

      int main()
      {
	  // UTF-8 data with BOM
	  std::ofstream{"text.txt"} << "\ufeffz\u6c34\U0001d10b";

	  // read the UTF-8 file, skipping the BOM
	  std::wifstream fin{"text.txt"};
	  fin.imbue(std::locale(fin.getloc(),
				new	std::codecvt_utf8<wchar_t,     0x10ffff,
     std::consume_header>));

	  for (wchar_t c; fin.get(c);)
	      std::cout << std::hex << std::showbase << (std::wint_t)c << '\n';
      }

Output:
      0x7a
      0x6c34
      0x1d10b

See also
			      converts	between  character  encodings, including
     UTF-8, UTF-16,
	codecvt 	      UTF-32
			      (class template)
	codecvt_utf8
	(C++11) 	      converts between UTF-8 and UCS-2/UCS-4
	(deprecated in C++17) (class template)
	(removed in C++26)
	codecvt_utf16
	(C++11) 	      converts between UTF-16 and UCS-2/UCS-4
	(deprecated in C++17) (class template)
	(removed in C++26)
	codecvt_utf8_utf16
	(C++11) 	      converts between UTF-8 and UTF-16
	(deprecated in C++17) (class template)
	(removed in C++26)

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