C++学习笔记36:类模板

template<typename T>class A
{
public:
    template<typename U> T f(const U &u);
};
template<typename T> template<typename U>
T A<T>::f(const U &u)
{

}

//队列
#include <iostream>
#include <cstdlib>
//空队列异常类
class EQueueEmpty {};
//队列项类前置声明
template<typename T> class JuQueueItem;
//队列类
template<typename T> class JuQueue
{
public:
    JuQueue:_head(NULL),_tail(NULL){}
    virtual JuQueue();
    virtual void Enter(const T &item);
    virtual T Leave();
    bool IsEmpty() const { return _head == 0; }
private:
    JuQueueItem<T> *_head, *_tail;
};
//队列项类，单项链表结构
template<typename T> class JuQueueItem
{
    friend class JuQueue<T>;
public:
    JuQueueItem(const T &item):_item(item),_next(0){}
private:
    T _item;
    JuQueueItem<T> *_next;
};
//队列类析构函数
template<typename T> JuQueue<T>::~JuQueue()
{
    while (!IsEmpty())
    {
        Leave();
    }
}
//入队
template<typename T> void JuQueue<T>::Enter(const T &item)
{
    JuQueueItem<T> *p = new JuQueueItem<T>(item);
    if (IsEmpty())
        _head = _tail = p;
    else
        _tail->_next = p, _tail = p;
}

//出列
template<typename T> T JuQueue<T>::Leave()
{
    if (IsEmpty())
        throw EQueueEmpty();
    JuQueueItem<T> *p = _head;
    T _retval = p->_item;
    _head = _head->_next;
    delete p;
    return _retval;
}

int main()
{
    JuQueue<int> *p = new JuQueue<int>;
    for (int i = 0; i < 10; i++)
    {
        p->Enter(i);
    }
    std::cout << p->Leave() << std::endl;

    int *r = new int(10), *p = new int(20);
    JuQueue<int*>*t = new JuQueue<int*>;
    t->Enter(r);
    t->Enter(q);
    int *s = t->Leave();
    std::cout << *s << std::endl;

    return 0;
}