std::binary_function

 

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unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

Defined in header <functional>
template< class Arg1, class Arg2, class Result > struct binary_function;		(deprecated in C++11) (removed in C++17)

See More

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

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<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';
}

Output:

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

See also

function (C++11)	copyable wrapper of any copy constructible callable object (class template)
move_only_function (C++23)	move-only wrapper of any callable object that supports qualifiers in a given call signature (class template)
ptr_fun (deprecated in C++11)(removed in C++17)	creates an adaptor-compatible function object wrapper from a pointer to function (function template)
pointer_to_binary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible wrapper for a pointer to binary function (class template)
unary_function (deprecated in C++11)(removed in C++17)	adaptor-compatible unary function base class (class template)