std::codecvt_mode

 

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Localizations library

Locales and facets
Locales
has_facet use_facet	locale
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
ctype facets
ctype ctype_byname ctype<char>	codecvt codecvt_byname
numeric facets
num_get num_put	numpunct numpunct_byname
collate facets
collate	collate_byname
time facets
time_get time_get_byname	time_put time_put_byname
monetary facets
money_get money_put	moneypunct moneypunct_byname
messages facets
messages	messages_byname
Character classification and conversion
Character classification
isspace isblank (C++11) iscntrl isupper islower isalpha	isdigit ispunct isxdigit isalnum isprint isgraph
Conversions
toupper tolower	wstring_convert (C++11/17*) wbuffer_convert (C++11/17*)
Code conversion facets
codecvt_utf8 (C++11/17*) codecvt_utf16 (C++11/17*)	codecvt_utf8_utf16 (C++11/17*) codecvt_mode (C++11/17*)
C locale
LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME	setlocale localeconv lconv

 

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.

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.

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

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