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>::
From cppreference.com
< cpp | string | char traits
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
Parameters
| a, b | - | character values to compare |
Return value
1)
true if a and b are equal, false
2)
true if a is less than b, false
Complexity
Constant.
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