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std::codecvt_mode

From cppreference.com
< cpp‎ | locale
Defined in header <codecvt>
enum codecvt_mode {

    consume_header = 4,
    generate_header = 2,
    little_endian = 1

};
(since C++11)
(deprecated in C++17)

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.

[edit] 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_header consume the byte order mark, if present at the start of input 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.

[edit] Example

The following example demonstrates consuming the UTF-8 BOM:

#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 UTF8 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

[edit] See also

converts between character encodings, including UTF-8, UTF-16, UTF-32
(class template) [edit]
(C++11)(deprecated in C++17)
converts between UTF-8 and UCS2/UCS4
(class template) [edit]
(C++11)(deprecated in C++17)
converts between UTF-16 and UCS2/UCS4
(class template) [edit]
(C++11)(deprecated in C++17)
converts between UTF-8 and UTF-16
(class template) [edit]