Question

C++中，一个类模板的内部又嵌套了一个类模板，语法应该是怎么样的

template <typename T>
class Stack {
private:
typedef struct Node {
T data;
struct Node *next;
} Node;
Node *top;
unsigned int length;
public:
template<typename V>
class const_iterator {
friend class Stack<V>;
private:
const Node *p;
public:
explicit const_iterator(Node *ptr);
const V& operator*();
const_iterator& operator++();
const const_iterator operator++(int );
// const const_iterator<V>& operator--();
//const const_iterator<V>& operator--(int );
bool operator==(const const_iterator& iter) const;
bool operator!=(const const_iterator& iter) const;
};

Stack();
unsigned int getLength() const;
void push(T data);
T pop();
T getTop() const;
const_iterator<T> begin() const;
const_iterator<T> end() const;
virtual ~Stack();
protected:

};

template <typename T>
Stack<T>::Stack():top(0), length(0)
{
}

template <typename T>
unsigned int Stack<T>::getLength() const
{
return length;
}

template <typename T>
void Stack<T>::push(T data)
{
Node *p = new Node;
p->data = data;
p->next = top;
top = p;
++length;
}

template <typename T>
T Stack<T>::pop()
{
Node *p = top;
T data = p->data;
top = top->next;
--length;
delete p;
return data;
}

template <typename T>
T Stack<T>::getTop() const
{
return top->data;
}

template <typename T>
Stack<T>::const_iterator<T> Stack<T>::begin() const
{
return const_iterator<T>::const_iterator(top);
}

template <typename T>
Stack<T>::const_iterator<T> Stack<T>::end() const
{
return const_iterator<T>::const_iterator(0);
}

template <typename T>
Stack<T>::~Stack()
{
while(length) {
pop();
}
}

template <typename T>
Stack<T>::const_iterator<T>::const_iterator(Node *ptr):p(ptr)
{
}

template <typename T>
const T& Stack<T>::const_iterator<T>::operator*()
{
return this->p->data;
}

template <typename T>
Stack<T>::const_iterator<T>& Stack<T>::const_iterator<T>::operator++()
{
p = p->next;
return *this;
}

template <typename T>
Stack<T>::const const_iterator<T> Stack<T>::const_iterator<T>::operator++(int )
{
const_iterator<T> tmp = *this;
p = p->next;
return tmp;
}
//const const_iterator<T>& operator--();
//const const_iterator<T>& operator--(int );

template <typename T>
bool Stack<T>::const_iterator<T>::operator==(const const_iterator<T>& iter) const
{
return p == iter.p;
}

template <typename T>
bool Stack<T>::const_iterator<T>::operator!=(const const_iterator<T>& iter) const
{
return !(p == iter.p);
}
以上是我写的，编译不过，有错误，希望各位大牛能解释一下
现在代码不在手边，晚上新开一个问题，上面的代码我自己修改过了，就只有一个错误，const_iterator里重载后置++运算符这个函数有问题，编译器是gcc 4.8.0，操作系统是Ubuntu 10.04， IDE用的是codeblocks 12.11

刚才在Visual Studio 2010 里试了一下，可以编译通过，但是仍然不知道为什么gcc下不行

Answer 1

写模板辛苦了……

template <typename T>
class Stack {
private:
typedef struct Node {
T data;
struct Node *next;
} Node;
Node *top;
unsigned int length;
public:
class const_iterator {
friend class Stack<T>;
private:
const Node *p;
public:
explicit const_iterator(Node *ptr);
const T& operator*();
const_iterator& operator++();
const const_iterator operator++(int );
// const const_iterator<V>& operator--();
//const const_iterator<V>& operator--(int );
bool operator==(const const_iterator& iter) const;
bool operator!=(const const_iterator& iter) const;
};

Stack();
unsigned int getLength() const;
void push(T data);
T pop();
T getTop() const;
const_iterator begin() const;
const_iterator end() const;
virtual ~Stack();
protected:

};

template <typename T>
Stack<T>::Stack():top(0), length(0)
{
}

template <typename T>
unsigned int Stack<T>::getLength() const
{
return length;
}

template <typename T>
void Stack<T>::push(T data)
{
Node *p = new Node;
p->data = data;
p->next = top;
top = p;
++length;
}

template <typename T>
T Stack<T>::pop()
{
Node *p = top;
T data = p->data;
top = top->next;
--length;
delete p;
return data;
}

template <typename T>
T Stack<T>::getTop() const
{
return top->data;
}

template <typename T>
typename Stack<T>::const_iterator Stack<T>::begin() const
{
return Stack<T>::const_iterator(top);
}

template <typename T>
typename Stack<T>::const_iterator Stack<T>::end() const
{
return const_iterator<T>::const_iterator(0);
}

template <typename T>
Stack<T>::~Stack()
{
while(length) {
pop();
}
}

template <typename T>
Stack<T>::const_iterator::const_iterator(Node *ptr):p(ptr)
{
}

template <typename T>
const T& Stack<T>::const_iterator::operator*()
{
return this->p->data;
}

template <typename T>
typename Stack<T>::const_iterator& Stack<T>::const_iterator::operator++()
{
p = p->next;
return *this;
}

template <typename T>
const typename Stack<T>::const_iterator Stack<T>::const_iterator::operator++(int )
{
const_iterator<T> tmp = *this;
p = p->next;
return tmp;
}
//const const_iterator<T>& operator--();
//const const_iterator<T>& operator--(int );

template <typename T>
bool Stack<T>::const_iterator::operator==(const typename Stack<T>::const_iterator& iter) const
{
return p == iter.p;
}

template <typename T>
bool Stack<T>::const_iterator::operator!=(const typename Stack<T>::const_iterator& iter) const
{
return !(p == iter.p);
}

1、模板类中的某个“类型”（class或者typedef都算）表示的时候要在前面加typename，不然编译器会认为它是成员变量或者成员函数
2、你的const_iterator在Stack<T>里面，故可以使用T作为类型，不进一步指定V也没有关系的
3、这代码我只是给你改到编译能通过而已，没有进一步调试运行是什么情况

追答

两个都用模板的情况下，我尝试了好久两边都过不去。

可能你可以参考一下boost里面一些库的写法，那个库里面一大堆变态至极的模板……

追问

我新开过一个提问的，那里的代码在Visual Studio 2010下是可以编译通过的，但是gcc下就是不行，只有你回答的最好，就采纳了。

Answer 2

1、const_iterator 应该是普通类

2、使用typename高速编译器Stack<T>是一个类型， 防止报error C2143

修改后代码如下：

template <typename T>
class Stack
{
private:
typedef struct Node
{
T data;
struct Node *next;
} Node;
Node *top;
unsigned int length;
public:
class const_iterator{
friend class Stack<T>;
private:
const Node *p;
public:
explicit const_iterator(Node *ptr);
const T& operator*();
const_iterator& operator++();
const const_iterator operator++(int );        // const const_iterator<V>& operator--();        //const const_iterator<V>& operator--(int );
bool operator==(const const_iterator& iter) const;
bool operator!=(const const_iterator& iter) const;
};
Stack();
unsigned int getLength() const;
void push(T data);
T pop();
T getTop() const;
const_iterator begin() const;
const_iterator end() const;
virtual ~Stack();protected:
};
template <typename T>Stack<T>::Stack():top(0), length(0)
{};
template <typename T>unsigned int Stack<T>::getLength() const
{
return length;
};
template <typename T>void Stack<T>::push(T data)
{
Node *p = new Node;
p->data = data;
p->next = top;
top = p;
++length;
};
template <typename T>T Stack<T>::pop()
{
Node *p = top;
T data = p->data;
top = top->next;
--length;
delete p;
return data;
};
template <typename T> T Stack<T>::getTop() const
{
return top->data;
};
template <typename T> typename Stack<T>::const_iterator Stack<T>::begin() const
{
return const_iterator::const_iterator(top);
};
template <typename T>
typename Stack<T>::const_iterator
Stack<T>::end() const
{
return const_iterator::const_iterator(0);
}
template <typename T> Stack<T>::~Stack()
{
while(length)
{
pop();
}
}
template <typename T> Stack<T>::const_iterator::const_iterator(Node *ptr):p(ptr)
{}
template <typename T>const T& Stack<T>::const_iterator::operator*()
{    return this->p->data;}
template <typename T> typename Stack<T>::const_iterator& Stack<T>::const_iterator::operator++()
{    p = p->next;    return *this;}
template <typename T>  const typename Stack<T>::const_iterator Stack<T>::const_iterator::operator++(int )
{    const_iterator tmp = *this;    p = p->next;    return tmp;}//const const_iterator<T>& operator--();//const const_iterator<T>& operator--(int );
template <typename T>bool Stack<T>::const_iterator::operator==(const const_iterator& iter) const
{    return p == iter.p;}
template <typename T>bool Stack<T>::const_iterator::operator!=(const const_iterator& iter) const{    return !(p == iter.p);}

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追问

　　首先，const_itertor不是普通类，即使不用模板参数V，它依然是个类模板，因为它嵌套在类模板内部。如果const_iterator是按照我这样的写法的话，所有的const_iterator的成员函数实现部分有问题，我自己修改过了，但是用gcc 4.8.0，编译的话，const_iterator中重载后置++运算符的那个函数有问题，提示要加typename，但是我加上typename依然不对。

Answer 3

通常, operator自会操作自己的容器, 所以, 你只需要简单的直接用前面的T即可,不需要再定义V.

直接类似下面:

struct Node;
template <typename T>
class Stack {
public:
    class const_iterator {
        friend class Stack<T>;
    private:
        const Node *p;
    public:
        explicit const_iterator(Node *ptr);
        const T& operator*();
    };
    Stack();
    virtual ~Stack();
};

追问

这个我知道，我只是想试试看如果是类模板嵌套的话应该怎么写

Answer 4

main函数都没有啊，而且从头看下来太吃力，很多语法错误