From cppreference.com
Function object for performing comparisons. Deduces the parameter types of the function call operator from the arguments (but not the return type).
Nested types
Member functions
operator()
checks if the first argument is less than the second
(public member function)std::ranges::less::operator()
template<classT,classU>constexprbooloperator()(T&&t,U&&u)const;Given the expression std::forward<T>(t)<std::forward<U>(u) as expr:
If expr results in a call to
operator< comparing pointers, given the
of t and u as P:
If the converted t precedes the converted u (both are of type P) in the
implementation-defined strict total order over pointers
, returns true, otherwise returns false.
If the conversion sequence from T to P or the conversion sequence from U to P is not
, the behavior is undefined.
Otherwise:
Returns the result of expr.
If std::totally_ordered_with<T,U> is not modeled, the behavior is undefined.
This overload participates in overload resolution only if std::totally_ordered_with<T,U> is satisfied.
If there exists an expression expr1 of type T and an expression expr2 of U, such that the comparison results of expr1 and expr2 violate
(rules are defined below), the behavior is undefined.
The comparison results of expr1 and expr2 follow strict total ordering only if exactly one of the following expressions is true:
std::ranges::less{}(expr1,expr2)
std::ranges::less{}(expr2,expr1)
std::ranges::equal_to{}(expr1,expr2)
Notes
Unlike
, std::ranges::less requires all six comparison operators <, <=, >, >=, == and != to be valid (via the
constraint).
Example
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++20 syntactic checks were relaxed while comparing pointers only semantic requirements are relaxed See also
function object implementing x<y
(class template)