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# std::ctype

From cppreference.com
< cpp‎ | locale

Defined in header `<locale>` |  |
template< class CharT > class ctype; |  |

Class ctype encapsulates character classification features. All stream input operations performed through std::basic_istream<charT> use the std::ctype<charT> of the locale imbued in the stream to identify whitespace characters for input tokenization. Stream output operations apply std::ctype<charT>::widen() to narrow-character arguments prior to output.

Inheritance diagram

Two standalone (locale-independent) specializations are provided by the standard library:

Defined in header `<locale>`
`std::ctype<char>` | provides narrow character equivalents of the minimal "C" locale classification. This specialization uses table lookup for character classification
std::ctype<wchar_t> | provides wide character classification appropriate to the native character set

In addition, every locale object constructed in a C++ program implements its own (locale-specific) versions of these specializations.

### [edit] Member types

Member type | Definition
`char_type` | `CharT`

### [edit] Member functions

(constructor) | constructs a new ctype facet (public member function)
(destructor) | destructs a ctype facet (protected member function)
is | invokes `do_is` (public member function) [edit]
scan_is | invokes `do_scan_is` (public member function) [edit]
scan_not | invokes `do_scan_not` (public member function) [edit]
toupper | invokes `do_toupper` (public member function) [edit]
tolower | invokes `do_tolower` (public member function) [edit]
widen | invokes `do_widen` (public member function) [edit]
narrow | invokes `do_narrow` (public member function) [edit]

### [edit] Member objects

static std::locale::id id | id of the locale (public member object)

### [edit] Protected member functions

do_is [virtual] | classifies a character or a character sequence (virtual protected member function) [edit]
do_scan_is [virtual] | locates the first character in a sequence that conforms to given classification (virtual protected member function) [edit]
do_scan_not [virtual] | locates the first character in a sequence that fails given classification (virtual protected member function) [edit]
do_toupper [virtual] | converts a character or characters to uppercase (virtual protected member function) [edit]
do_tolower [virtual] | converts a character or characters to lowercase (virtual protected member function) [edit]
do_widen [virtual] | converts a character or characters from `char` to `charT` (virtual protected member function) [edit]
do_narrow [virtual] | converts a character or characters from `charT` to `char` (virtual protected member function) [edit]

## 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 a ctype other than ctype<char> to tokenize a CSV file

Run this code

    #include <iostream>
    #include <locale>
    #include <sstream>

    struct csv_whitespace : std::ctype<wchar_t>
    {
        bool do_is(mask m, char_type c) const
        {
            if ((m & space) && c == L' ') {
                return false; // space will NOT be classified as whitespace
            }
            if ((m & space) && c == L',') {
                return true; // comma will be classified as whitespace
            }
            return ctype::do_is(m, c); // leave the rest to the parent class
        }
    };

    int main()
    {
        std::wstring in = L"Column 1,Column 2,Column 3\n123,456,789";
        std::wstring token;

        std::wcout << "default locale:\n";
        std::wistringstream s1(in);
        while (s1 >> token) {
            std::wcout << "  " << token << '\n';
        }

        std::wcout << "locale with modified ctype:\n";
        std::wistringstream s2(in);
        s2.imbue(std::locale(s2.getloc(), new csv_whitespace()));
        while (s2 >> token) {
            std::wcout << "  " << 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<char> | specialization of std::ctype for type char (class template specialization)
ctype_base | defines character classification categories (class template)
ctype_byname | creates a ctype facet for the named locale (class template)

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