Difference between revisions of "cpp/locale/codecvt mode"
From cppreference.com
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===Constants=== | ===Constants=== | ||
| − | |||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc header | locale}} | + | {{dsc header|locale}} |
| − | {{dsc hitem | Value | Meaning }} | + | {{dsc hitem|Value|Meaning }} |
| − | {{dsc | {{tt|little_endian}} | + | {{dsc|{{tt|little_endian}}|assume the input is in little-endian byte order (applies to UTF-16 input only, the default is big-endian) }} |
| − | {{dsc | {{tt|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}} | + | {{dsc|{{tt|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}} |
| − | {{dsc | {{tt|generate_header}} | output the byte order mark at the start of the output sequence }} | + | {{dsc|{{tt|generate_header}}|output the byte order mark at the start of the output sequence }} |
{{dsc end}} | {{dsc end}} | ||
The recognized byte order marks are: | The recognized byte order marks are: | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc | {{tt|0xfe 0xff}} | UTF-16 big-endian }} | + | {{dsc|{{tt|0xfe 0xff}}|UTF-16 big-endian }} |
| − | {{dsc | {{tt|0xff 0xfe}} | UTF-16 little-endian }} | + | {{dsc|{{tt|0xff 0xfe}}|UTF-16 little-endian }} |
| − | {{dsc | {{tt|0xef 0xbb 0xbf}} | UTF-8 (no effect on endianness)}} | + | {{dsc|{{tt|0xef 0xbb 0xbf}}|UTF-8 (no effect on endianness)}} |
{{dsc end}} | {{dsc end}} | ||
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|The following example demonstrates consuming the UTF-8 BOM: | |The following example demonstrates consuming the UTF-8 BOM: | ||
|code= | |code= | ||
| + | #include <codecvt> | ||
| + | #include <cwchar> | ||
#include <fstream> | #include <fstream> | ||
#include <iostream> | #include <iostream> | ||
| + | #include <locale> | ||
#include <string> | #include <string> | ||
| − | |||
| − | |||
int main() | int main() | ||
{ | { | ||
// UTF-8 data with BOM | // UTF-8 data with BOM | ||
| − | std::ofstream | + | std::ofstream{"text.txt"} << "\ufeffz\u6c34\U0001d10b"; |
// read the UTF8 file, skipping the BOM | // read the UTF8 file, skipping the BOM | ||
| − | std::wifstream fin | + | std::wifstream fin{"text.txt"}; |
fin.imbue(std::locale(fin.getloc(), | fin.imbue(std::locale(fin.getloc(), | ||
new std::codecvt_utf8<wchar_t, 0x10ffff, std::consume_header>)); | new std::codecvt_utf8<wchar_t, 0x10ffff, std::consume_header>)); | ||
for (wchar_t c; fin.get(c);) | for (wchar_t c; fin.get(c);) | ||
| − | std::cout << std::hex << std::showbase << c << '\n'; | + | std::cout << std::hex << std::showbase << (std::wint_t)c << '\n'; |
} | } | ||
|output= | |output= | ||
| Line 61: | Line 61: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/locale/dsc codecvt}} | + | {{dsc inc|cpp/locale/dsc codecvt}} |
| − | {{dsc inc | cpp/locale/dsc codecvt_utf8}} | + | {{dsc inc|cpp/locale/dsc codecvt_utf8}} |
| − | {{dsc inc | cpp/locale/dsc codecvt_utf16}} | + | {{dsc inc|cpp/locale/dsc codecvt_utf16}} |
| − | {{dsc inc | cpp/locale/dsc codecvt_utf8_utf16}} | + | {{dsc inc|cpp/locale/dsc codecvt_utf8_utf16}} |
{{dsc end}} | {{dsc end}} | ||
{{langlinks|de|es|fr|it|ja|pt|ru|zh}} | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | ||
Revision as of 07:07, 26 January 2023
| Defined in header <codecvt>
|
||
| enum codecvt_mode { consume_header = 4, |
(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 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
See also
| converts between character encodings, including UTF-8, UTF-16, UTF-32 (class template) | |
| (C++11)(deprecated in C++17)(removed in C++26) |
converts between UTF-8 and UCS-2/UCS-4 (class template) |
| (C++11)(deprecated in C++17)(removed in C++26) |
converts between UTF-16 and UCS-2/UCS-4 (class template) |
| (C++11)(deprecated in C++17)(removed in C++26) |
converts between UTF-8 and UTF-16 (class template) |
