C++仿函数(一)(举例multiplies)

仿函数

1. 仿函数不是函数，是一个class或者struct
2. 仿函数重定义操作符()

根据传入的参数个数分为unary_function(1个参数)和 binary_function(2个参数)

multiplies 的定义

// STRUCT TEMPLATE multiplies
template
	struct multiplies
	{	// functor for operator*
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty result_type;

	constexpr _Ty operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator* to operands
		return (_Left * _Right);
		}
	};

使用示例

#include
#include
using namespace std;
int main(int argc, char** argv){
    int x = multiplies()(3,4);
    if(not_equal_to()(x,10)){
        cout<

类似的使用

定义的位置：

less greater greater_equal less_equal not_equal_to
logical_and logical_or logical_not
minus plus divide modulus negate

template
	struct plus
	{	// functor for operator+
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty result_type;

	constexpr _Ty operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator+ to operands
		return (_Left + _Right);
		}
	};

		// STRUCT TEMPLATE minus
template
	struct minus
	{	// functor for operator-
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty result_type;

	constexpr _Ty operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator- to operands
		return (_Left - _Right);
		}
	};

		// STRUCT TEMPLATE multiplies
template
	struct multiplies
	{	// functor for operator*
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty result_type;

	constexpr _Ty operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator* to operands
		return (_Left * _Right);
		}
	};

		// STRUCT TEMPLATE equal_to
template
	struct equal_to
	{	// functor for operator==
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef bool result_type;

	constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator== to operands
		return (_Left == _Right);
		}
	};

		// STRUCT TEMPLATE not_equal_to
template
	struct not_equal_to
	{	// functor for operator!=
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef bool result_type;

	constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator!= to operands
		return (_Left != _Right);
		}
	};

		// STRUCT TEMPLATE greater
template
	struct greater
	{	// functor for operator>
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef bool result_type;

	constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator> to operands
		return (_Left > _Right);
		}
	};

		// STRUCT TEMPLATE less
template
	struct less
	{	// functor for operator<
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef bool result_type;

	constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator< to operands
		return (_Left < _Right);
		}
	};

		// STRUCT TEMPLATE greater_equal
template
	struct greater_equal
	{	// functor for operator>=
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef bool result_type;

	constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator>= to operands
		return (_Left >= _Right);
		}
	};

		// STRUCT TEMPLATE less_equal
template
	struct less_equal
	{	// functor for operator<=
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty first_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef _Ty second_argument_type;
	_CXX17_DEPRECATE_ADAPTOR_TYPEDEFS typedef bool result_type;

	constexpr bool operator()(const _Ty& _Left, const _Ty& _Right) const
		{	// apply operator<= to operands
		return (_Left <= _Right);
		}
	};