std::ctype<char>

Defined in header `<locale>`
template<> class 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

(constructor)	constructs a new std::ctype<char> facet (public member function)
(destructor)	destructs a std::ctype<char> facet (protected member function)
table	obtains the character classification table (public member function)
classic_table [static]	obtains the "C" locale character classification table (public static member function)
is	classifies a character or a character sequence, using the classification table (public member function)
scan_is	locates the first character in a sequence that conforms to given classification, using the classification table (public member function)
scan_not	locates the first character in a sequence that fails given classification, using the classification table (public member function)
toupper	invokes `do_toupper` (public member function of `std::ctype`)
tolower	invokes `do_tolower` (public member function of `std::ctype`)
widen	invokes `do_widen` (public member function of `std::ctype`)
narrow	invokes `do_narrow` (public member function of `std::ctype`)

[edit] Protected member functions

do_toupper [virtual]	converts a character or characters to uppercase (virtual protected member function of `std::ctype`)
do_tolower [virtual]	converts a character or characters to lowercase (virtual protected member function of `std::ctype`)
do_widen [virtual]	converts a character or characters from `char` to `charT` (virtual protected member function of `std::ctype`)
do_narrow [virtual]	converts a character or characters from `charT` to `char` (virtual protected member function of `std::ctype`)

[edit] Member objects

static std::locale::id id [static]	id of the locale (public static member constant)
static const std::size_t table_size [static]	size of the classification table, at least 256 (public static member constant)

Inherited from std::ctype_base

Member types

Type	Definition
`mask`	unspecified bitmask type (enumeration, integer type, or bitset)

Member constants

space [static]	the value of `mask` identifying whitespace character classification (public static member constant)
print [static]	the value of `mask` identifying printable character classification (public static member constant)
cntrl [static]	the value of `mask` identifying control character classification (public static member constant)
upper [static]	the value of `mask` identifying uppercase character classification (public static member constant)
lower [static]	the value of `mask` identifying lowercase character classification (public static member constant)
alpha [static]	the value of `mask` identifying alphabetic character classification (public static member constant)
digit [static]	the value of `mask` identifying digit character classification (public static member constant)
punct [static]	the value of `mask` identifying punctuation character classification (public static member constant)
xdigit [static]	the value of `mask` identifying hexadecimal digit character classification (public static member constant)
blank [static] (C++11)	the value of `mask` identifying blank character classification (public static member constant)
alnum [static]	alpha \| digit (public static member constant)
graph [static]	alnum \| punct (public static member constant)

[edit] Example

The following example demonstrates modification of ctype<char> to tokenize comma-separated values

Run this code

#include <iostream>
#include <vector>
#include <locale>
#include <sstream>
 
// 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';
}

Output:

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

[edit] See also

ctype	defines character classification tables (class template)
ctype_base	defines character classification categories (class template)
ctype_byname	creates a ctype facet for the named locale (class template)

Language
Standard library headers
Concepts
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)