std::binary_function

template<
    class Arg1,
    class Arg2, 
    class Result
> struct binary_function;

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

std::binary_function does not define operator(); it is expected that derived classes will define this. std::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 std::binary_function is an easy way to make them compatible with those adaptors.

std::binary_function is deprecated in C++11 and removed in C++17.

Member types

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<char> v1{'A', 'B', 'C', 'D', 'E'};
    std::vector<char> v2{'E', 'D', 'C', 'B', 'A'};
    std::vector<bool> v3(v1.size());
 
    std::transform(v1.begin(), v1.end(), v2.begin(), v3.begin(), std::not2(same()));
 
    std::cout << std::boolalpha;
    for (std::size_t i = 0; i < v1.size(); ++i)
        std::cout << v1[i] << " != " << v2[i] << " : " << v3[i] << '\n';
}

A != E : true
B != D : true
C != C : false
D != B : true
E != A : true

See also