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

< cpp‎ | locale‎ | ctype
Localizations library
Locales and facets
Facet category base classes
ctype facets
numeric facets
collate facets
time facets
monetary facets
messages facets
Character classification and conversion
Character classification
Code conversion facets
C locale
Text encoding identifications
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]