# std::less<void>

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< cpp‎ | utility‎ | functional

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

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`, `std::ranges::greater_equal`, and std::compare_three_way | (since C++20)

### 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

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