Defined in header
Function object for performing comparisons. Deduces the parameter types of the function call operator from the arguments (but not the return type).
 Implementation-defined strict total order over pointers
The function call operator yields the implementation-defined strict total order over pointers if the
< operator between arguments invokes a built-in comparison operator for a pointer, even if the built-in
< operator does not.
The implementation-defined strict total order is consistent with the partial order imposed by built-in comparison operators (
>=), and consistent among following standard function objects:
- std::less, std::greater, std::less_equal, and std::greater_equal, when the template argument is a pointer type or void
- std::ranges::equal_to, std::ranges::not_equal_to, std::ranges::less, std::ranges::greater, std::ranges::less_equal, std::ranges::greater_equal, and std::compare_three_way
 Member types
||/* unspecified */|
 Member functions
| checks if the first argument is less than the second |
(public member function)
template< class T, class U >
requires std::totally_ordered_with<T, U> // with different semantic requirements
u, equivalent to return std::forward<T>(t) < std::forward<U>(u);, except when that expression resolves to a call to a built-in operator< comparing pointers.
When a call would not invoke a built-in operator comparing pointers, the behavior is undefined if std::totally_ordered_with<T, U> is not modeled.
When a call would invoke a built-in operator comparing pointers of type
P, the result is instead determined as follows:
- Returns true if the (possibly converted) value of the first argument precedes the (possibly converted) value of the second argument in the implementation-defined strict total ordering over all pointer values of type
P. This strict total ordering is consistent with the partial order imposed by the built-in operators
- Otherwise, returns false.
The behavior is undefined unless the conversion sequences from both
P are equality-preserving.
 Equality preservation
Expressions declared in requires-expressions of the standard library concepts are required to be equality-preserving (except where stated otherwise).
std::ranges::less requires all six comparison operators
!= to be valid (via the
|This section is incomplete|
Reason: no 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|
|LWG 3530||C++20||syntactic checks were relaxed while comparing pointers||only semantic requirements relaxed|
 See also
| function object implementing x < y |