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

< cpp‎ | locale‎ | ctype
Defined in header <locale>
bool is( mask m, CharT c ) const;
const CharT* is( const CharT* low, const CharT* high, mask* vec ) const;
virtual bool do_is( mask m, CharT c ) const;
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 [lowhigh), 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.


[edit] Parameters

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

[edit] Return value

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

[edit] Example

#include <cstddef>
#include <iostream>
#include <locale>
#include <utility>
#include <vector>
// 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+" << static_cast<wint_t>(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

[edit] See also

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