less_equal Struct

Artikkeli
08/03/2021

A binary predicate that performs the less-than-or-equal-to operation (operator<=) on its arguments.

Syntax

template <class Type = void>
struct less_equal : public binary_function <Type, Type, bool>
{
    bool operator()(const Type& Left, const Type& Right) const;
};

// specialized transparent functor for operator<=
template <>
struct less_equal<void>
{
  template <class T, class U>
  auto operator()(T&& Left, U&& Right) const
    -> decltype(std::forward<T>(Left) <= std::forward<U>(Right));
};

Parameters

Type, T, U
Any type that supports an operator<= that takes operands of the specified or inferred types.

Left
The left operand of the less-than-or-equal-to operation. The unspecialized template takes an lvalue reference argument of type Type. The specialized template does perfect forwarding of lvalue and rvalue reference arguments of inferred type T.

Right
The right operand of the less-than-or-equal-to operation. The unspecialized template takes an lvalue reference argument of type Type. The specialized template does perfect forwarding of lvalue and rvalue reference arguments of inferred type U.

Return Value

The result of Left <= Right. The specialized template does perfect forwarding of the result, which has the type returned by operator<=.

Remarks

The binary predicate less_equal<Type> provides a strict weak ordering of a set of element values of type Type into equivalence classes, if and only if this type satisfies the standard mathematical requirements for being so ordered. The specializations for any pointer type yield a total ordering of elements, in that all elements of distinct values are ordered with respect to each other.

Example

// functional_less_equal.cpp
// compile with: /EHsc
#define _CRT_RAND_S
#include <stdlib.h>
#include <vector>
#include <algorithm>
#include <functional>
#include <cstdlib>
#include <iostream>

int main( )
{
   using namespace std;
   vector <int> v1;
   vector <int>::iterator Iter1;
   vector <int>::reverse_iterator rIter1;
   unsigned int randomNumber;

   int i;
   for ( i = 0 ; i < 5 ; i++ )
   {
      if ( rand_s( &randomNumber ) == 0 )
      {
         // Convert the random number to be between 1 - 50000
         // This is done for readability purposes
         randomNumber = ( unsigned int) ((double)randomNumber /
            (double) UINT_MAX * 50000) + 1;

         v1.push_back( randomNumber );
      }
   }
   for ( i = 0 ; i < 3 ; i++ )
   {
      v1.push_back( 2836 );
   }

   cout << "Original vector v1 = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")" << endl;

   // To sort in ascending order,
   // use the binary predicate less_equal<int>( )
   sort( v1.begin( ), v1.end( ), less_equal<int>( ) );
   cout << "Sorted vector v1 = ( " ;
   for ( Iter1 = v1.begin( ) ; Iter1 != v1.end( ) ; Iter1++ )
      cout << *Iter1 << " ";
   cout << ")" << endl;
}

Original vector v1 = (31247 37154 48755 15251 6205 2836 2836 2836)
Sorted vector v1 = (2836 2836 2836 6205 15251 31247 37154 48755)

Jaa