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.

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.

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

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

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)

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)
Technical Specifications

Member functions
ctype::ctype
ctype::~ctype
ctype::isctype::do_is
ctype::scan_isctype::do_scan_is
ctype::scan_notctype::do_scan_not
ctype::toupperctype::do_toupper
ctype::tolowerctype::do_tolower
ctype::widenctype::do_widen
ctype::narrowctype::do_narrow
Member functions of ctype<char>
ctype<char>::ctype
ctype<char>::~ctype
ctype<char>::table
ctype<char>::classic_table
ctype<char>::is
ctype<char>::scan_is
ctype<char>::scan_not