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# std::codecvt_mode

From cppreference.com
< cpp‎ | locale

Defined in header `<locale>` |  |
enum codecvt_mode { consume_header = 4, generate_header = 2, little_endian = 1 }; |  |

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

Run this code

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

    int main()
    {
        // UTF-8 data with BOM
        std::ofstream("text.txt") << u8"\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 << c << '\n';
    }

Output:

    0x7a
    0x6c34
    0x1d10b

### [edit] See also

codecvt | converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template) [edit]
codecvt_utf8 (C++11) | converts between UTF-8 and UCS2/UCS4 (class template) [edit]
codecvt_utf16 (C++11) | converts between UTF-16 and UCS2/UCS4 (class template) [edit]
codecvt_utf8_utf16 (C++11) | converts between UTF-8 and UTF-16 (class template) [edit]

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