c++模板（类型依赖）说明例子

#include <iostream>
#include <list>
template <typename T>
class CCustomerList
{
public:
	void push(T item)
	{
		m_customer.push_back(item);
	}
	void show_item()
	{
		CCIterator it = m_customer.begin();
		while(it != m_customer.end())
		{
			std::cout<<(*it)<<std::endl;
			++it;
		}
	}
private:
	typedef std::list<T> CustomerContainer;
	typedef typename CustomerContainer::iterator CCIterator;
	CustomerContainer m_customer;
};
int main(int argc, char *argv[])
{
	CCustomerList<int> c;
	for(int i=0; i<10; ++i) c.push(i);
	c.show_item();
	return 0;
}

 这里说的是CCustomerList里的

typedef typename CustomerContainer::iterator CCIterator;

语句。

在这条语句中必须加上typename关键字，不然编译时会报错。

根据《effective STL》里的解释： CustomerContainer::iterator 是一个依赖形式类型参数T的一种类型，所以必须在它前面放上typename这个词。

template关键字还可以用在中间：

Template names can not only occur after a :: but also after a -> or . in a class member access. You need to insert the keyword there too.

如：Protocol_v2<alloc_t> * pack = alloc->template malloc<Protocol_v2<alloc_t> >();

更多内容见：

http://stackoverflow.com/questions/12477755/what-kind-of-template-is-this

http://stackoverflow.com/questions/610245/where-and-why-do-i-have-to-put-the-template-and-typename-keywords