std::ctype<char>
From cppreference.com
| Defined in header <locale>
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template<>
class ctype<char>;
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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
Nested types
| Type | Definition |
char_type
|
char
|
Data members
| Member | Description |
std::locale::id id [static]
|
the identifier of the facet |
const std::size_t table_size [static]
|
size of the classification table, at least 256 |
Member functions
constructs a new ctype<char> facet (public member function) | |
destructs a ctype<char> facet (protected member function) | |
| obtains the character classification table (public member function) | |
[static] |
obtains the "C" locale character classification table (public static member function) |
| classifies a character or a character sequence, using the classification table (public member function) | |
| locates the first character in a sequence that conforms to given classification, using the classification table (public member function) | |
| locates the first character in a sequence that fails given classification, using the classification table (public member function) | |
invokes do_toupper (public member function of std::ctype<CharT>)
| |
invokes do_tolower (public member function of std::ctype<CharT>)
| |
invokes do_widen (public member function of std::ctype<CharT>)
| |
invokes do_narrow (public member function of std::ctype<CharT>)
|
Protected member functions
[virtual] |
converts a character or characters to uppercase (virtual protected member function of std::ctype<CharT>)
|
[virtual] |
converts a character or characters to lowercase (virtual protected member function of std::ctype<CharT>)
|
[virtual] |
converts a character or characters from char to CharT (virtual protected member function of std::ctype<CharT>)
|
[virtual] |
converts a character or characters from CharT to char (virtual protected member function of std::ctype<CharT>)
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Inherited from std::ctype_base
Nested types
| Type | Definition |
mask
|
unspecified BitmaskType 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
| defines character classification tables (class template) | |
| defines character classification categories (class) | |
| represents the system-supplied std::ctype for the named locale (class template) |