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 type | definition | notes |
|---|
| first_argument_type | T | Type of the first argument in member operator() |
| second_argument_type | T | Type of the second argument in member operator() |
| result_type | bool | Type 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)