# equal_to Struct

A binary predicate that tests whether a value of a specified type is equal to another value of that type.

``````template<class Type>
struct equal_to : public binary_function<Type, Type, bool>
{
bool operator()(
const Type& _Left,
const Type& _Right
) const;
};
``````

## Parameters

• _Left
The left operand of type Type in the equality to be tested.

• _Right
The right operand of type Type in the equality to be tested.

## Return Value

true if _Left equals _Right; false if _Left does not equal _Right.

## 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 the built-in numeric and pointer types satisfy this requirement.

## Example

``````// functional_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 ( ),
equal_to<double>( ) );

cout << "The result of the element-wise equal_to comparison\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 equal_to comparison between v1 & v2 is: ( 1 1 0 1 0 1 )