NAME¶

std::less - std::less

Synopsis¶

Defined in header <functional>
template<> (since C++14)
class less<void>;

std::less<void> is a specialization of std::less with parameter and return type
deduced.

Member functions¶

operator() tests if lhs compares less than rhs
(public member function)

std::less<void>::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¶

std::forward<T>(lhs) < std::forward<U>(rhs).

If a built-in operator comparing pointers is called, the result is consistent with
the implementation-defined strict total order over pointers.

Exceptions¶

May throw implementation-defined exceptions.

Example¶

// Run this code

#include <algorithm>
#include <functional>

constexpr bool strictly_negative(int lhs)
{
return std::less<>()(lhs, 0);
}

int main()
{
constexpr signed low = 010;
constexpr unsigned high = 10;
std::less<> less{};
static_assert(less(low, high));

constexpr static auto arr = {0, -1, -2, -3, -4, -5};
static_assert(!std::all_of(arr.begin(), arr.end(), strictly_negative));
static_assert(std::all_of(arr.begin() + 1, arr.end(), strictly_negative));
}

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 2562 C++98 the pointer total order might be guaranteed to be consistent
inconsistent