Defined in header <locale> | ||
---|---|---|
public: char narrow( CharT c, char dflt ) const; | (1) | |
public: const CharT* narrow( const CharT* beg, const CharT* end, char dflt, char* dst ) const; | (2) | |
protected: virtual char do_narrow( CharT c, char dflt ) const; | (3) | |
protected: virtual const CharT* do_narrow( const CharT* beg, const CharT* end, char dflt, char* dst ) const; | (4) |
do_narrow
of the most derived class.c
to multibyte representation if the character can be represented with a single byte (for example, ASCII characters in UTF-8 encoding are single bytes). Returns dflt
if such conversion does not exist.[beg, end)
, writes narrowed characters (or dflt
whenever narrowing fails) to the successive locations in the character array pointed to by dst
.Narrowing is always successful and is always reversible (by calling widen()
) for all characters from the basic source character set (latin letters, digits, and punctuations required to write a C++ program).
Narrowing, if successful, preserves all character classification categories known to is()
.
Narrowing of any digit character guarantees that if the result is subtracted from the character literal '0'
, the difference equals the digit value of the original character.
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 |
dflt
if narrowing failsend
#include <locale> #include <iostream> void try_narrow(const std::ctype<wchar_t>& f, wchar_t c) { char n = f.narrow(c, 0); if (n) { std::wcout << '\'' << c << "' narrowed to " << +(unsigned char)n << '\n'; } else { std::wcout << '\'' << c << "' could not be narrowed\n"; } } int main() { std::locale::global(std::locale("en_US.utf8")); std::wcout.imbue(std::locale()); std::wcout << std::hex << std::showbase << "In US English UTF-8 locale:\n"; auto& f = std::use_facet<std::ctype<wchar_t>>(std::locale()); try_narrow(f, L'A'); try_narrow(f, L'A'); try_narrow(f, L'ě'); std::locale::global(std::locale("cs_CZ.iso88592")); auto& f2 = std::use_facet<std::ctype<wchar_t>>(std::locale()); std::wcout << "In Czech ISO-8859-2 locale:\n"; try_narrow(f2, L'A'); try_narrow(f2, L'A'); try_narrow(f2, L'ě'); }
Output:
In US English UTF-8 locale: 'A' narrowed to 0x41 'A' could not be narrowed 'ě' could not be narrowed In Czech ISO-8859-2 locale: 'A' narrowed to 0x41 'A' could not be narrowed 'ě' narrowed to 0xec
invokes do_widen (public member function) |
|
narrows characters (public member function of std::basic_ios<CharT,Traits> ) |
|
narrows a wide character to a single-byte narrow character, if possible (function) |
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