自定义STL游标实现虚拟容器(2)

最新推荐文章于 2021-09-12 23:19:53 发布

pandaxcl

最新推荐文章于 2021-09-12 23:19:53 发布

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分类专栏： STL 文章标签： iterator generator class iostream struct algorithm

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本文介绍了一种名为虚拟迭代器的C++模板类，该类可以用于生成数学函数序列并进行运算，如正弦和余弦函数的计算、求和及内积计算等。通过这种方式，展示了如何灵活运用STL算法进行数学处理。

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#include <iostream> 
#include <algorithm> 
#include <numeric> 
#include <iterator> 
#include <functional> 
#include <cmath> 
template<class T,class Generator> 
class virtual_iterator:public std::iterator<std::forward_iterator_tag,T> 
{ 
public:
	typedef T value_type;
	virtual_iterator(size_t const&i):_i(i){}
	value_type& operator*()
	{
		return _value=_generator(_i);
	}
	const value_type& operator++()
	{
		_i++;return _value=_generator(_i);
	}
	const value_type& operator++(int)
	{
		_i++;
		return _value=_generator(_i);
	}
	bool operator==(const virtual_iterator& other) const
	{
		return _i == other._i;
	}
	bool operator!=(const virtual_iterator& other) const
	{
		return _i != other._i;
	}
private:
	size_t _i;
	value_type _value;
	Generator _generator;
};
struct Sin { double operator()(const size_t&i) { return sin(i); } }; 
struct Cos { double operator()(const size_t&i) { return cos(i); } }; 
template<class T,class Generator> 
void display(virtual_iterator<T,Generator>&begin,virtual_iterator<T,Generator>&end,const char*str)
{
	std::cout << str ;
	std::copy(begin,end,std::ostream_iterator<T>(std::cout," ")); 
        std::cout << std::endl; 
}
int main() 
{
	std::cout.precision(20);
	{
		virtual_iterator<double,Sin> begin(0),end(5);
		display(begin,end,"正弦函数:");
		double result=std::accumulate(begin,end,0.0);
		std::cout << "正弦函数求和 = [" << result<< "]" << std::endl;
	}
	std::cout << std::endl;
	{
		virtual_iterator<double,Cos> begin(0),end(5);
		display(begin,end,"余弦函数:"); 
                double result=std::accumulate(begin,end,0.0); 
                std::cout << "余弦函数求和 = [" << result<< "]" << std::endl;
	}
	std::cout << std::endl;
	{
		virtual_iterator<double,Sin> sin_begin(0),sin_end(5);
		virtual_iterator<double,Cos> cos_begin(0),cos_end(5);
		display(sin_begin,sin_end,"正弦函数a:");
		display(cos_begin,cos_end,"余弦函数b:");
		double result=std::inner_product(sin_begin,sin_end,cos_begin,0.0);
                std::cout << "a和b的内积 = [" << result<< "]" << std::endl;
	}
	return 0;
}