std::ctype<CharT>::is,std::ctype<CharT>::do_is (3) - Linux Manuals

std::ctype<CharT>::is,std::ctype<CharT>::do_is: std::ctype<CharT>::is,std::ctype<CharT>::do_is


std::ctype<CharT>::is,std::ctype<CharT>::do_is - std::ctype<CharT>::is,std::ctype<CharT>::do_is


Defined in header <locale>
public: (1)
bool is(mask m, CharT c) const;
public: (2)
const CharT* is(const CharT* low, const CharT* high, mask* vec) const;
protected: (3)
virtual bool do_is(mask m, CharT c) const;
protected: (4)
virtual const CharT* do_is(const CharT* low, const CharT* high, mask* vec) const;

1,2) public member function, calls the protected virtual member function do_is of the most derived class.
3) Checks if the character c is classified by the mask m
4) For every character in the character array [low, high), identifies the complete classification mask (e.g. digit|xdigit|alnum|print|graph for the digit '0' in the default locale), and stores the masks in the corresponding elements of the array pointed to by vec


c - character to classify
m - mask to use for classifying a single character
low - pointer to the first character in an array of characters to classify
high - one past the end pointer for the array of characters to classify
vec - pointer to the first element of the array of masks to fill

Return value

1,3) true if c is classified by m
2,4) high


// Run this code

  #include <locale>
  #include <utility>
  #include <vector>
  #include <iostream>

  // utility wrapper to make locale-bound facets destructible
  template<class Facet>
  struct deletable_facet : Facet
      template<class ...Args>
      deletable_facet(Args&& ...args) : Facet(std::forward<Args>(args)...) {}
      ~deletable_facet() {}

  int main()
      // classify a single character using the default locale
      auto& f = std::use_facet<std::ctype<char>>(std::locale());
      char c = '0';
      if (, c)) // or isdigit(c, locale());
          std::cout << "'" << c << "' is a digit\n";

      // classify every character in a string using a named locale
      deletable_facet<std::ctype_byname<wchar_t>> f2("en_US.utf8");
      std::wstring str = L"z\u00df\u6c34\U0001d10b";
      std::vector<std::ctype_base::mask> vec(str.size());[0], &str[0] + str.size(), &vec[0]);

      for (std::size_t n = 0; n < str.size(); ++n) {
         std::cout << std::hex << "U+" << str[n] << " is: ";
         if (vec[n] & std::ctype_base::alnum)
            std::cout << " alnum ";
         if (vec[n] & std::ctype_base::punct)
            std::cout << " punct ";
         std::cout << '\n';


  '0' is a digit
  U+7a is: alnum
  U+df is: alnum
  U+6c34 is: alnum
  U+1d10b is: punct

See also

         classifies a character or a character sequence, using the classification table
is (public member function of std::ctype<char>)
         classifies a wide character according to the specified LC_CTYPE category
iswctype (function)