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
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std::char_traits
Member functions
char_traits::eqchar_traits::lt
static bool eq( char_type a, char_type b );
(1)
(constexpr since C++11)(noexcept since C++11)
static bool 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<unsigned char>(a) == static_cast<unsigned char>(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<unsigned char>(a) < static_cast<unsigned char>(b), if
char_typeis char, - a < b otherwise.
See CharTraits for the general requirements on character traits for X::eq and X::lt.
[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 unsigned char |
- ↑ Most implementations call std::memcmp() for efficiency, which interprets the data as arrays of unsigned char. If char is signed on such implementations, std::char_traits <char> fails to satisfy the requirements of CharTraits.