std::char_traits

Defined in header `<string>`
template< class CharT > class char_traits;

The char_traits class is a traits class template that abstracts basic character and string operations for a given character type. The defined operation set is such that generic algorithms almost always can be implemented in terms of it. It is thus possible to use such algorithms with almost any possible character or string type, just by supplying customized char_traits class.

The char_traits class template serves as a basis for explicit instantiations. The user can provide a specialization for any custom character types. Several specializations are defined for the standard character types. The values of the member typedefs are as follows.

Instantiation	`char_type`	`int_type`	`off_type`	`pos_type`	`state_type`
`char_traits<char>`	`char`	`int`	`std::streamoff`	`std::streampos`	`std::mbstate_t`
`char_traits<wchar_t>`	`wchar_t`	`std::wint_t`	`std::wstreamoff`	`std::wstreampos`	`std::mbstate_t`
`char_traits<char16_t>` (C++11)	`char16_t`	`std::uint_least16_t`	`std::streamoff`	`std::u16streampos`	`std::mbstate_t`
`char_traits<char32_t>` (C++11)	`char32_t`	`std::uint_least32_t`	`std::streamoff`	`std::u32streampos`	`std::mbstate_t`

The char_traits class template satisfies the requirements of CharTraits.

Member types

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

Member functions

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

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 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) {
        auto const ua (std::toupper(a));
        while ( n-- != 0 ) 
        {
            if (std::toupper(*s) == ua)
                return s;
            s++;
        }
        return nullptr;
    }
};
 
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

std::char_traits

Member types

Member functions

Example

See also