std::ctype<char> - cppreference.com

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# std::ctype<char>

From cppreference.com
< cpp‎ | locale

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

### [edit] Member types

Member type | Definition
`char_type` | `char`

### [edit] Member functions

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

### [edit] Protected member functions

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

### [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)

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