table of contents
std::less(3) | C++ Standard Libary | std::less(3) |
NAME¶
std::less - std::less
Synopsis¶
Defined in header <functional>
template<> (since C++14)
class less<void>;
std::less<> is a specialization of std::less with parameter and return
type deduced.
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 (
<=>,
(since C++20)<, >, <=, and >=), 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, (since
C++20)
std::ranges::greater_equal, and std::compare_three_way
Member types¶
Member type Definition
is_transparent /* unspecified */
Member functions¶
operator() tests if the lhs compares less than rhs
(public member function)
std::less<>::operator()
template< class T, class U>
constexpr auto operator()( T&& lhs, U&& rhs ) const
-> decltype(std::forward<T>(lhs) <
std::forward<U>(rhs));
Returns the result of std::forward<T>(lhs) <
std::forward<U>(rhs).
Parameters¶
lhs, rhs - values to compare
Return value¶
The result of std::forward<T>(lhs) < std::forward<U>(rhs).
If the comparison between both arguments resolves to a built-in comparison
operator
for a pointer type, the implementation-defined strict total order is used for
comparison after converting both arguments to pointers.
Exceptions¶
May throw implementation-defined exceptions.
Notes¶
The member type is_transparent indicates to the caller that this
function object is
a transparent function object: it accepts arguments of arbitrary types and
uses
perfect forwarding, which avoids unnecessary copying and conversion when the
function object is used in heterogeneous context, or with rvalue arguments.
In
particular, template functions such as std::set::find and
std::set::lower_bound make
use of this member type on their Compare types.
Example¶
This section is incomplete
Reason: no example
2022.07.31 | http://cppreference.com |