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std::ctype

From cppreference.com
< cpp‎ | locale
 
C++
 
Localization library
 
std::ctype
 
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.

cpp/locale/ctype basecpp/locale/locale/facetstd-ctype-inheritance.svg

Inheritance diagram

Contents

Specializations

The standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):

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

Member types

Member type Definition
char_type CharT

Member functions

 constructs a new ctype facet
(public member function)
destructs a ctype facet
(protected member function)
invokes do_is
(public member function) [edit]
invokes do_scan_is
(public member function) [edit]
invokes do_scan_not
(public member function) [edit]
invokes do_toupper
(public member function) [edit]
invokes do_tolower
(public member function) [edit]
invokes do_widen
(public member function) [edit]
invokes do_narrow
(public member function) [edit]

Member objects

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

Protected member functions

[virtual]
 classifies a character or a character sequence
(virtual protected member function) [edit]
[virtual]
 locates the first character in a sequence that conforms to given classification
(virtual protected member function) [edit]
[virtual]
 locates the first character in a sequence that fails given classification
(virtual protected member function) [edit]
[virtual]
 converts a character or characters to uppercase
(virtual protected member function) [edit]
[virtual]
 converts a character or characters to lowercase
(virtual protected member function) [edit]
[virtual]
 converts a character or characters from char to CharT
(virtual protected member function) [edit]
[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)

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 base 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);
    csv_whitespace* my_ws = new csv_whitespace;
    s2.imbue(std::locale(s2.getloc(), my_ws));
    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

See also

 specialization of std::ctype for type char
(class template specialization) [edit]
defines character classification categories
(class) [edit]
represents the system-supplied std::ctype for the named locale
(class template) [edit]
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