equal_to


class template
<functional> 
template <class T> struct equal_to;

Function object class for equality comparison

This class defines function objects for the equality comparison operation.

Generically, function objects are instances of a class with member function operator() defined. This member function allows the object to be used with the same syntax as a regular function call, and therefore it can be used in templates instead of a pointer to a function.

equal_to has its operator() member defined such that it returns true if its two arguments compare equal to each other using operator==, and false otherwise.

This class is derived from binary_function and is defined as:

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template <class T> struct equal_to : binary_function <T,T,bool> {
  bool operator() (const T& x, const T& y) const
    {return x==y;}
};


Objects of this class can be used with some standard algorithms such as mismatch, search or unique.

Members

T operator() (const T& x, const T& y)
Member function returning the result of the comparison x==y.


Example

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// equal_to example
#include <iostream>
#include <utility>
#include <functional>
#include <algorithm>
using namespace std;

int main () {
  pair<int*,int*> ptiter;
  int foo[]={10,20,30,40,50};
  int bar[]={10,20,40,80,160};
  ptiter=mismatch ( foo, foo+5, bar, equal_to<int>() );
  cout << "First mistmatching pair is: " << *ptiter.first;
  cout << " and " << *ptiter.second << endl;
  return 0;
}


Output:

First mismatching pair is: 30 and 40


See also

not_equal_to Function object class for non-equality comparison (class template)
greater Function object class for greater-than inequality comparison (class template)
less Function object class for less-than inequality comparison (class template)
greater_equal Function object class for greater-than-or-equal-to comparison (class template)
less_equal Function object class for less-than-or-equal-to comparison (class template)
binary_function Binary function object base class (class template)