std::ctype<char>

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Execution support library (C++26)

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, table lookup is used to classify characters. The base class std::ctype<char> implements character classification appropriate to the native character set (usually, but not necessarily equivalent to the minimal "C" locale). The classification rules can be extended or modified 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 leaest 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 of a CSV file

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

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)