std::binary_function

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Defined in header `<functional>`

template <typename Argument1Type, typename Argument2Type, typename ResultType> struct binary_function;		(deprecated)

binary_function is a base class for creating function objects with two arguments.

binary_function does not define operator(); it is expected that derived classes will define this. binary_function provides only three types - first_argument_type, second_argument_type and result_type - defined by the template parameters.

Some standard library function object adaptors, such as std::not2, require the function objects they adapt to have certain types defined; std::not2 requires the function object being adapted to have two types named first_argument_type and second_argument_type. Deriving function objects that take two arguments from binary_function is an easy way to make them compatible with those adaptors.

binary_function is deprecated in C++11. Its functionality has been made obsolete by std::function.

[edit] Member types


Type	Definition

`first_argument_type`	`Argument1Type`

`second_argument_type`	`Argument2Type`

`result_type`	`ResultType`

[edit] Example

#include <algorithm>
#include <functional>
#include <iostream>
#include <vector>
 
struct same : std::binary_function<int, int, bool>
{
    bool operator()(int a, int b) const { return a == b; }
};
 
int main()
{
    std::vector<int> v1;
    std::vector<int> v2;
    for (int i = 0; i < 10;        ++i) v1.push_back(i);
    for (int i = 0; i < v1.size(); ++i) v2.push_back(10 - i);
 
    std::vector<bool> v3(v1.size());
 
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(), std::not2(same()));
 
    /* C++11 solution:
        // Cast to std::function<bool (int, int)> somehow - even with a lambda
        std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(),
            std::not2(std::function<bool (int, int)>(
              [](int a, int b){ return a == b; }
            ))
        );
    */
 
    std::cout.setf(std::ios_base::boolalpha);
    for (int i = 0; i < v1.size(); ++i)
        std::cout << v1[i] << ' ' << v2[i] << ' ' << v3[i] << '\n';
}

Output:

0 10 true
1 9 true
2 8 true
3 7 true
4 6 true
5 5 false
6 4 true
7 3 true
8 2 true
9 1 true

[edit] See also


function (C++11)	wraps callable object of any type with specified function call signature (class template)

ptr_fun (deprecated)	creates an adaptor-compatible function object wrapper from a pointer to function (function template)

pointer_to_binary_function (deprecated)	adaptor-compatible wrapper for a pointer to binary function (class template)

unary_function (deprecated)	adaptor-compatible unary function base class (class template)