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 order 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)