std::ctype<CharT>::widen,do_widen (3) - Linux Manuals

std::ctype<CharT>::widen,do_widen: std::ctype<CharT>::widen,do_widen


std::ctype<CharT>::widen,do_widen - std::ctype<CharT>::widen,do_widen


Defined in header <locale>
public: (1)
CharT widen( char c ) const;
public: (2)
const char* widen( const char* beg, const char* end, CharT* dst ) const;
protected: (3)
virtual CharT do_widen( char c ) const;
protected: (4)
virtual const char* do_widen( const char* beg, const char* end, CharT* dst ) const;

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 (latin letters, digits, and punctuations required to write a C++ program) 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().


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) end


// 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()
      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

      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');


  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
narrow (public member function)
       widens characters
widen (public member function of std::basic_ios<CharT,Traits>)
       widens a single-byte narrow character to wide character, if possible
btowc (function)