# std::binary_function

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< cpp‎ | utility‎ | functional

Defined in header `<functional>` |  |
template< class Arg1, class Arg2, class Result > struct binary_function; |  | (until C++17) (deprecated since c++11)

`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 and removed in C++17.

### Member types

Type | Definition
`first_argument_type` | `Arg1`
`second_argument_type` | `Arg2`
`result_type` | `Result`

### Example

Run this code

    #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{ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        std::vector<int> v2{10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 };
        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';
    }

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
    10 0 true

### See also

function (C++11) | wraps callable object of any type with specified function call signature (class template)
ptr_fun (until C++17) | creates an adaptor-compatible function object wrapper from a pointer to function (function template)
pointer_to_binary_function (until C++17) | adaptor-compatible wrapper for a pointer to binary function (class template)
unary_function (until C++17) | adaptor-compatible unary function base class (class template)

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