std:: ctype <char>

This specialization of std::ctype encapsulates character classification features for type char . Unlike general-purpose std::ctype , which uses virtual functions, this specialization uses table lookup to classify characters (which is generally faster).

The base class std::ctype < char > implements character classification equivalent to the minimal "C" locale. The classification rules can be extended or modified if constructed with a non-default classification table argument, if constructed as std:: ctype_byname < char > or as a user-defined derived facet. All std::istream formatted input functions are required to use std::ctype < char > for character classing during input parsing.

Inheritance diagram

Nested types

Data members

Member functions

Protected member functions

Example

#include <cstddef>
#include <iostream>
#include <locale>
#include <sstream>
#include <vector>
 
// This ctype facet classifies commas and endlines as whitespace
struct csv_whitespace : std::ctype<char>
{
    static const mask* make_table()
    {
        // make a copy of the "C" locale table
        static std::vector<mask> v(classic_table(), classic_table() + table_size);
        v[','] |=  space; // comma will be classified as whitespace
        v[' '] &= ~space; // space will not be classified as whitespace
        return &v[0];
    }
 
    csv_whitespace(std::size_t refs = 0) : ctype(make_table(), false, refs) {}
};
 
int main()
{
    std::string in = "Column 1,Column 2,Column 3\n123,456,789";
    std::string token;
 
    std::cout << "Default locale:\n";
    std::istringstream s1(in);
    while (s1 >> token)
        std::cout << "  " << token << '\n';
 
    std::cout << "Locale with modified ctype:\n";
    std::istringstream s2(in);
    s2.imbue(std::locale(s2.getloc(), new csv_whitespace));
    while (s2 >> token)
        std::cout << "  " << token << '\n';
}

Default locale:
  Column
  1,Column
  2,Column
  3
  123,456,789
Locale with modified ctype:
  Column 1
  Column 2
  Column 3
  123
  456
  789

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also