binary_function
class template
<functional>
template <class Arg1, class Arg2, class Result> struct binary_function;
Binary function object base class
This is a base class for standard binary function objects.
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.
In the case of binary function objects, this operator() member function takes two parameters.
binary_function is just a base class, from which specific binary function objects are derived. It has no operator() member defined (derived classes are expected to define this) - it simply has three public data members that are typedefs of the template parameters. It is defined as:
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template <class Arg1, class Arg2, class Result>
struct binary_function {
typedef Arg1 first_argument_type;
typedef Arg2 second_argument_type;
typedef Result result_type;
};
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Members
- first_argument_type
- Alias of the first template parameter, which is the type for the first argument in member operator().
- second_argument_type
- Alias of the second template parameter, which is the type for the second argument in member operator().
- result_type
- Alias of the third template parameter, which is the return type in member operator().
Example
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// binary_function example
#include <iostream>
#include <functional>
using namespace std;
struct Compare : public binary_function<int,int,bool> {
bool operator() (int a, int b) {return (a==b);}
};
int main () {
Compare Compare_object;
Compare::first_argument_type input1;
Compare::second_argument_type input2;
Compare::result_type result;
cout << "Please enter first number: ";
cin >> input1;
cout << "Please enter second number: ";
cin >> input2;
result = Compare_object (input1,input2);
cout << "Numbers " << input1 << " and " << input2;
if (result)
cout << " are equal.\n";
else
cout << " are not equal.\n";
return 0;
}
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Possible output:
Please enter first number: 2
Please enter second number: 33
Numbers 2 and 33 are not equal.
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See also
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