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)