not_equal_to Struct

A binary predicate that performs the inequality operation (operator!=) on its arguments.

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

// specialized transparent functor for operator!=
template<>
   struct not_equal_to<void>
   {
      template<class Type1, class Type2>
      auto operator()(Type1&& Left, Type2&& Right) const
      -> decltype(std::forward<Type1>(Left)
         != std::forward<Type2>(Right));
   };

Parameters

• Type, Type1, Type2
  Any type that supports an operator!= that takes operands of the specified or inferred types.

• Left
  The left operand of the inequality 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 Type1.

• Right
  The right operand of the inequality 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 Type2.

Return Value

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

Remarks

The objects of type Type must be equality-comparable. This requires that the operator!= defined on the set of objects satisfies the mathematical properties of an equivalence relation. All of the built-in numeric and pointer types satisfy this requirement.

Example

// functional_not_equal_to.cpp
// compile with: /EHsc
#include <vector>
#include <functional>
#include <algorithm>
#include <iostream>

using namespace std;

int main( )
{
   vector <double> v1, v2, v3 (6);
   vector <double>::iterator Iter1, Iter2, Iter3;
   
   int i;
   for ( i = 0 ; i <= 5 ; i+=2 )
   {
      v1.push_back( 2.0 *i );
      v1.push_back( 2.0 * i + 1.0 );
   }

   int j;
   for ( j = 0 ; j <= 5 ; j+=2 )
   {
      v2.push_back( - 2.0 * j );
      v2.push_back( 2.0 * j + 1.0 );
   }

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

   cout << "The vector v2 = ( " ;
   for ( Iter2 = v2.begin( ) ; Iter2 != v2.end( ) ; Iter2++ )
      cout << *Iter2 << " ";
   cout << ")" << endl;

   // Testing for the element-wise equality between v1 & v2
   transform ( v1.begin( ), v1.end( ), v2.begin( ), v3.begin ( ), 
      not_equal_to<double>( ) );

   cout << "The result of the element-wise not_equal_to comparsion\n"
      << "between v1 & v2 is: ( " ;
   for ( Iter3 = v3.begin( ) ; Iter3 != v3.end( ) ; Iter3++ )
      cout << *Iter3 << " ";
   cout << ")" << endl;
}

The vector v1 = ( 0 1 4 5 8 9 )
The vector v2 = ( -0 1 -4 5 -8 9 )
The result of the element-wise not_equal_to comparsion
between v1 & v2 is: ( 0 0 1 0 1 0 )

Requirements

Header: <functional>

Namespace: std

See Also

Reference

Standard Template Library