std::ctype<char>

 

C++

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Technical specifications

Symbols index

External libraries

 

Localization library

Locales and facets
Locales
has_facet use_facet	locale
Facet category base classes
ctype_base codecvt_base messages_base	time_base money_base
ctype facets
ctype ctype<char> ctype_byname	codecvt codecvt_byname
numeric facets
num_get num_put	numpunct numpunct_byname
collate facets
collate	collate_byname
time facets
time_get time_put	time_get_byname time_put_byname
monetary facets
money_get money_put	moneypunct moneypunct_byname
messages facets
messages	messages_byname

Character classification and conversion
Character classification
isspace isblank (C++11) iscntrl	isupper islower isalpha	ispunct isdigit isxdigit	isalnum isprint isgraph

Character conversions

toupper

tolower

String and stream conversions

wstring_convert (C++11/17/26*)

wbuffer_convert (C++11/17/26*)

Text encoding identifications

text_encoding (C++26)

Unicode conversion facets

codecvt_utf8 (C++11/17/26*)

codecvt_utf16 (C++11/17/26*)

codecvt_utf8_utf16 (C++11/17/26*)

codecvt_mode (C++11/17/26*)

C library locales
LC_ALLLC_COLLATELC_CTYPELC_MONETARYLC_NUMERICLC_TIME	setlocale localeconv lconv

 

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

Member types

Member type	Definition
char_type	char

Member functions

(constructor)	constructs a new ctype<char> facet (public member function)
(destructor)	destructs a 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<CharT>)
tolower	invokes do_tolower (public member function of std::ctype<CharT>)
widen	invokes do_widen (public member function of std::ctype<CharT>)
narrow	invokes do_narrow (public member function of std::ctype<CharT>)

Protected member functions

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

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)

Example

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

Run this code

#include <cstddef>
#include <iostream>
#include <locale>
#include <sstream>
#include <vector>
 
// 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

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 695	C++98	table() and classic_table() were protected member functions	made them public

See also

ctype	defines character classification tables (class template)
ctype_base	defines character classification categories (class)
ctype_byname	represents the system-supplied std::ctype for the named locale (class template)