std::ctype<CharT>::widen, do_widen
From cppreference.com
| Defined in header <locale>
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| public: CharT widen( char c ) const; |
(1) | |
| public: const char* widen( const char* beg, const char* end, CharT* dst ) const; |
(2) | |
| protected: virtual CharT do_widen( char c ) const; |
(3) | |
| protected: virtual const char* do_widen( const char* beg, const char* end, CharT* dst ) const; |
(4) | |
1,2) public member function, calls the protected virtual member function
do_widen of the most derived class.3) Converts the single-byte character
c to the corresponding wide character representation using the simplest reasonable transformation. Typically, this applies only to the characters whose multibyte encoding is a single byte (e.g. U+0000-U+007F in UTF-8).4) For every character in the character array
[beg, end), writes the corresponding widened character to the successive locations in the character array pointed to by dst.Widening always returns a wide character, but only the characters from the basic source character set (until C++23)basic character set (since C++23) are guaranteed to have a unique, well-defined, widening transformation, which is also guaranteed to be reversible (by narrow()). In practice, all characters whose multibyte representation is a single byte are usually widened to their wide character counterparts, and the rest of the possible single-byte values are usually mapped into the same placeholder value, typically CharT(-1).
Widening, if successful, preserves all character classification categories known to is().
Parameters
| c | - | character to convert |
| dflt | - | default value to produce if the conversion fails |
| beg | - | pointer to the first character in an array of characters to convert |
| end | - | one past the end pointer for the array of characters to convert |
| dst | - | pointer to the first element of the array of char to fill |
Return value
1,3) widened character
2,4)
endExample
Run this code
#include <locale> #include <iostream> void try_widen(const std::ctype<wchar_t>& f, char c) { wchar_t w = f.widen(c); std::cout << "The single-byte character " << +(unsigned char)c << " widens to " << +w << '\n'; } int main() { std::locale::global(std::locale("cs_CZ.iso88592")); auto& f = std::use_facet<std::ctype<wchar_t>>(std::locale()); std::cout << std::hex << std::showbase << "In Czech ISO-8859-2 locale:\n"; try_widen(f, 'a'); try_widen(f, '\xdf'); // German letter ß (U+00df) in ISO-8859-2 try_widen(f, '\xec'); // Czech letter ě (U+011b) in ISO-8859-2 std::locale::global(std::locale("cs_CZ.utf8")); auto& f2 = std::use_facet<std::ctype<wchar_t>>(std::locale()); std::cout << "In Czech UTF-8 locale:\n"; try_widen(f2, 'a'); try_widen(f2, '\xdf'); try_widen(f2, '\xec'); }
Output:
In Czech ISO-8859-2 locale: The single-byte character 0x61 widens to 0x61 The single-byte character 0xdf widens to 0xdf The single-byte character 0xec widens to 0x11b In Czech UTF-8 locale: The single-byte character 0x61 widens to 0x61 The single-byte character 0xdf widens to 0xffffffff The single-byte character 0xec widens to 0xffffffff
See also
invokes do_narrow (public member function) | |
| widens characters (public member function of std::basic_ios<CharT,Traits>) | |
| widens a single-byte narrow character to wide character, if possible (function) |