C++

Reference

<functional>

class template
<functional>

std::equal_to

template <class T> struct equal_to;
Function object class for equality comparison
Binary function object class whose call returns whether its two arguments compare equal (as returned by operator ==).

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 function call.

It is defined with the same behavior 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;}
};
 
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template <class T> struct equal_to {
  bool operator() (const T& x, const T& y) const {return x==y;}
  typedef T first_argument_type;
  typedef T second_argument_type;
  typedef bool result_type;
};

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

Template parameters

T
Type of the arguments to compare by the functional call.
The type shall support the operation (operator==).

Member types

member typedefinitionnotes
first_argument_typeTType of the first argument in member operator()
second_argument_typeTType of the second argument in member operator()
result_typeboolType returned by member operator()

Member functions

bool operator() (const T& x, const T& y)
Member function returning whether the arguments compare equal (x==y).

Example

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// equal_to example
#include <iostream>     // std::cout
#include <utility>      // std::pair
#include <functional>   // std::equal_to
#include <algorithm>    // std::mismatch

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