std::char_traits<char>::eq/lt, std::char_traits<wchar_t>::eq/lt, std::char_traits<char8_t>::eq/lt, std::char_traits<char16_t>::eq/lt, std::char_traits<char32_t>::eq/lt
From cppreference.com
< cpp | string | char traits
staticbool eq( char_type a, char_type b ); | (1) | (constexpr since C++11) (noexcept since C++11) |
staticbool lt( char_type a, char_type b ); | (2) | (constexpr since C++11) (noexcept since C++11) |
Compares two characters.
1) Compares a and b for equality, behaves identically to
- static_cast<unsignedchar>(a)==static_cast<unsignedchar>(b), if
char_typeis char, - a == b otherwise.
2) Compares a and b in such a way that they are totally ordered, behaves identically to
- static_cast<unsignedchar>(a)<static_cast<unsignedchar>(b), if
char_typeis char, - a < b otherwise.
See CharTraits for the general requirements on character traits for X::eq and X::lt.
Contents |
[edit]Parameters
| a, b | - | character values to compare |
[edit]Return value
1)true if a and b are equal, false otherwise.
2)true if a is less than b, false otherwise.
[edit]Complexity
Constant.
[edit]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 467 | C++98 | for std::char_traits<char>, the semantics of eq() and lt()are the same as the built-in == and < on char respectively[1] | changed to built-in == and < on unsignedchar |
- ↑Most implementations call std::memcmp() for efficiency, which interprets the data as arrays of unsignedchar. If charis signed on such implementations, std::char_traits<char> fails to satisfy the requirements of CharTraits.
