C++ foreach

注意: 本人是原创, 如若发现雷同, 后果自负

C++ 11

C++ 11 是直接支持的, 判断__cpp_range_based_for的值, 如果是200907L就是支持

#include <iostream>
#include <vector>

int main(void)
{ 
	std::vector<int> vec{ 1,2,3,4,5};
	
#if __cpp_range_based_for >= 200907L
	for (int var : vec)
	{ 
		std::cout << var << std::endl;
	}
#endif
}

输出结果

1
2
3
4
5

C++ 11 之前

只能写一个类来控制
文件名: foreach.hpp

// foreach.hpp
#ifndef FOREACH_HPP
#define FOREACH_HPP

template <typename container_type>
class Foreach_container
{ 
public:

    Foreach_container(const container_type &c) : begin(c.begin()), end(c.end()) { }
    Foreach_container(container_type &c) : begin(c.begin()), end(c.end()) { }

    decltype(container_type().begin()) begin, end;
    bool f = true;
};

#define FOREACH(var, container) \ for (auto _container_ = in::Foreach_container<decltype(container)>(container); \ _container_.f && _container_.begin != _container_.end; \ ++_container_.begin, _container_.f = true) \ \ for (var = *_container_.begin; _container_.f; _container_.f = false)

#ifndef foreach
# define foreach FOREACH
#endif

#endif // FOREACH_HPP

使用方法

#include <iostream>
#include <vector>
#include "foreach.hpp"

int main(void)
{ 
	std::vector<int> vec{ 1,2,3,4,5};
	
	// 使用foreach宏
	foreach (int var, vec)
	{ 
		std::cout << var << std::endl;
	}
}

输出结果

1
2
3
4
5

结合

#include <iostream>
#include <vector>

#if __cpp_range_based_for >= 200907L

	#define FOREACH(var, container) for (var : container)
	
#else
	template <typename container_type>
	class Foreach_container
	{ 
	public:
	
	    Foreach_container(const container_type &c) : begin(c.begin()), end(c.end()) { }
	    Foreach_container(container_type &c) : begin(c.begin()), end(c.end()) { }
	
	    decltype(container_type().begin()) begin, end;
	    bool f = true;
	};
	
	#define FOREACH(var, container) \ for (auto _container_ = in::Foreach_container<decltype(container)>(container); \ _container_.f && _container_.begin != _container_.end; \ ++_container_.begin, _container_.f = true) \ \ for (var = *_container_.begin; _container_.f; _container_.f = false)
#endif

#ifndef foreach
# define foreach FOREACH
#endif

int main(void)
{ 
	std::vector<int> vec{ 1,2,3,4,5};
	
	// 使用foreach宏
	foreach (int var, vec)
	{ 
		std::cout << var << std::endl;
	}
}