std::char_traits

From cppreference.com

Defined in header `<string>`

template< class CharT > class char_traits;

The char_traits class defines the stream and string operation properties of a character type, such as the types used for manipulating the characters and character strings, as well as all the common operations for the given character type.

There is class template char_traits defined, which serves as a basis for explicit instantiations. It fulfills all requirements of Traits concept.

Also, several specializations are defined for most common character types which which has to specify the following members:

Instantiation	`char_type`	`int_type`	`off_type`	`pos_type`	`state_type`
char_traits<char>	char	int	streamoff	streampos	mbstate_t
char_traits<wchar_t>	wchar_t	wint_t	wstreamoff	wstreampos	mbstate_t
char_traits<char16_t> (C++11)	char16_t	int_least16_t	streamoff	u16streampos	mbstate_t
char_traits<char32_t> (C++11)	char32_t	int_least32_t	streamoff	u32streampos	mbstate_t


assign [static]	assigns a character (public static member function)

eq lt [static]	compares two characters (public static member function)

move [static]	moves one character sequence onto another (public static member function)

copy [static]	copies a character sequence (public static member function)

compare [static]	lexicographically compares two character sequences (public static member function)

length [static]	returns the length of a character sequence (public static member function)

find [static]	finds a character in a character sequence (public static member function)

to_char_type [static]	converts `int_type` to equivalent `char_type` (public static member function)

to_int_type [static]	converts `char_type` to equivalent `int_type` (public static member function)

eq_int_type [static]	compares two `int_type` values (public static member function)

eof [static]	returns an eof value (public static member function)

not_eof [static]	checks whether a character is eof value (public static member function)

[edit] Example

User-defined character traits may be used to provide case-insensitive comparison

#include <string>
#include <iostream>
#include <cctype>
 
struct ci_char_traits : public std::char_traits<char> {
    static bool eq(char c1, char c2) {
         return std::toupper(c1) == std::toupper(c2);
     }
    static bool ne(char c1, char c2) {
         return std::toupper(c1) != std::toupper(c2);
     }
    static bool lt(char c1, char c2) {
         return std::toupper(c1) <  std::toupper(c2);
    }
    static int compare(const char* s1, const char* s2, size_t n) {
        while( n-- != 0 ) {
            if( std::toupper(*s1) < std::toupper(*s2) ) return -1;
            if( std::toupper(*s1) > std::toupper(*s2) ) return 1;
            ++s1; ++s2;
        }
        return 0;
    }
    static const char* find(const char* s, int n, char a) {
        while( n-- > 0 && std::toupper(*s) != std::toupper(a) ) {
            ++s;
        }
        return s;
    }
};
 
typedef std::basic_string<char, ci_char_traits> ci_string;
 
std::ostream& operator<<(std::ostream& os, const ci_string& str) {
    return os.write(str.data(), str.size());
}
 
int main()
{
    ci_string s1 = "Hello";
    ci_string s2 = "heLLo";
    if(s1 == s2)
        std::cout << s1 << " and " << s2 << " are equal\n";
}

Output:

Hello and heLLo are equal

[edit] See also


basic_string	stores and manipulates sequences of characters (class template)

Language
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)


Type	Definition

`char_type`	`CharT`

`int_type`	an integer type that can hold all values of `char_type` plus `EOF`

`off_type`	implementation-defined

`pos_type`	implementation-defined

`state_type`	implementation-defined

std::char_traits

Contents

[edit] Member types

[edit] Member functions

[edit] Example

[edit] See also