std::less

 

C++

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Operator wrappers plus minus negate multiplies divides modulus bit_and bit_or bit_not (C++14)   bit_xor equal_to not_equal_to greater less greater_equal less_equal logical_and logical_or logical_not	Transparent operator wrappers plus<> (C++14) minus<> (C++14) negate<> (C++14) multiplies<> (C++14)   divides<> (C++14) modulus<> (C++14) bit_and<> (C++14) bit_or<> (C++14) bit_not<> (C++14) bit_xor<> (C++14) equal_to<> (C++14) not_equal_to<> (C++14) greater<> (C++14) less<> (C++14) greater_equal<> (C++14) less_equal<> (C++14) logical_and<> (C++14) logical_or<> (C++14) logical_not<> (C++14)
Negators not_fn (C++17) Searchers default_searcher (C++17) boyer_moore_searcher (C++17) boyer_moore_horspool_searcher (C++17)	Constrained comparators ranges::equal_to (C++20) ranges::not_equal_to (C++20) ranges::greater (C++20) ranges::less (C++20) ranges::greater_equal (C++20) ranges::less_equal (C++20) compare_three_way (C++20)
Old binders and adaptors
unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

Template:ddcl list begin <tr class="t-dsc-header">

<td>

Defined in header <functional>

</td>

<td></td> <td></td> </tr> <tr class="t-dcl ">

<td class="t-dcl-nopad">

template< class T >
struct less;

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<td class="t-dcl-nopad"> </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end

Function object for performing comparisons. Uses operator< on type T.

Implementation-defined strict total order over pointers

A specialization of std::less for any pointer type yields the implementation-defined strict total order, even if the built-in operator< 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(since C++14)

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

type	definition
result_type	bool
first_argument_type	T
second_argument_type	T

Member functions

operator()

checks if the first argument is less than the second (public member function)

std::less::operator()

bool operator()( const T& lhs, const T& rhs ) const;

Checks whether lhs is less than rhs.

Parameters

lhs, rhs

-

values to compare

Return value

true if lhs < rhs, false otherwise.

Exceptions

(none)

Possible implementation

bool operator()(const T &lhs, const T &rhs) const { return lhs < rhs; }

Example

Run this code

#include <functional>
#include <iostream>
 
template <typename A, typename B, typename U = std::less<int>>
bool f(A a, B b, U u = U()) {
 
    return u(a, b);
 
}
 
int main() {
 
    std::cout << std::boolalpha;
 
    std::cout << f(5, 20);
    std::cout << f(100, 10);
 
}

Output:

true
false

See also

Template:cpp/memory/dcl list owner less