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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

(1) 
static bool eq( char_type a, char_type b );
 (until C++11) 
static constexpr bool eq( char_type a, char_type b ) noexcept;
 (since C++11)
(2) 
static bool lt( char_type a, char_type b );
 (until C++11) 
static constexpr bool lt( char_type a, char_type b ) 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_type is 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_type is 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 otherwise.
2) true if a is less than b, false otherwise.

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
  1. 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.

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