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Difference between revisions of "cpp/utility/functional/less"

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< cpp‎ | utility‎ | functional
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[[de:cpp/utility/functional/less]]
 
[[de:cpp/utility/functional/less]]

Revision as of 20:14, 31 May 2013

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Function objects
Function invocation
(C++17)(C++23)
Identity function object
(C++20)
Transparent operator wrappers
(C++14)
(C++14)
(C++14)
(C++14)  
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)

Old binders and adaptors
(until C++17*)
(until C++17*)
(until C++17*)
(until C++17*)
(until C++17*)  
(until C++17*)
(until C++17*)(until C++17*)(until C++17*)(until C++17*)
(until C++20*)
(until C++20*)
(until C++17*)(until C++17*)
(until C++17*)(until C++17*)

(until C++17*)
(until C++17*)(until C++17*)(until C++17*)(until C++17*)
(until C++20*)
(until C++20*)
 
Defined in header <functional>
template< class T >
struct less;

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

Contents

Notes

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:

(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) << '\n';
    std::cout << f(100, 10) << '\n';
}

Output: 

true
false

See also

Template:cpp/memory/dcl list owner less
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