Thechar_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 a customizedchar_traits class.

Thechar_traits class template serves as a basis for explicit instantiations. The user canprovide a specialization for any custom character types. Several explicit specializations are provided for the standard character types (see below), other specializations are not required to satisfy the requirements ofCharTraits.

[edit]Specializations

The standard library provides the following standard specializations:

All these specializations satisfy the requirements ofCharTraits.

[edit]Member types

The standard specializations define the following member types required byCharTraits:

[edit]Member functions

The standard specializations define the following static member functions required byCharTraits:

[edit]Notes

CharTraits does not require defining the types and functions listed above as direct members, it only requires types likeX::type and expressions likeX::func(args) are valid and have the required semantics. Users-defined character traits can be derived from other character traits classes and only override some of their members, see the example below.

[edit]Example

#include <cctype>#include <iostream>#include <string>#include <string_view> struct ci_char_traits:public std::char_traits<char>{staticchar to_upper(char ch){returnstd::toupper((unsignedchar) ch);} staticbool eq(char c1,char c2){return to_upper(c1)== to_upper(c2);} staticbool lt(char c1,char c2){return to_upper(c1)< to_upper(c2);} staticint compare(constchar* s1,constchar* s2,std::size_t n){while(n--!=0){if(to_upper(*s1)< to_upper(*s2))return-1;if(to_upper(*s1)> to_upper(*s2))return1;++s1;++s2;}return0;} staticconstchar* find(constchar* s,std::size_t n,char a){constauto ua{to_upper(a)};while(n--!=0){if(to_upper(*s)== ua)return s;            s++;}return nullptr;}}; template<class DstTraits,class CharT,class SrcTraits>constexprstd::basic_string_view<CharT, DstTraits>    traits_cast(conststd::basic_string_view<CharT, SrcTraits> src)noexcept{return{src.data(), src.size()};} int main(){usingnamespace std::literals; constexprauto s1="Hello"sv;constexprauto s2="heLLo"sv; if(traits_cast<ci_char_traits>(s1)== traits_cast<ci_char_traits>(s2))std::cout<< s1<<" and "<< s2<<" are equal\n";}

Hello and heLLo are equal

[edit]See also

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