error C2259: ✀linkQueue✀ : cannot instantiate abstract class due to following members:

不好意思，一开始看错了。

这是queue里的声明：
virtual void enQueue(const char &x) = 0;
这是linkQueue里的：
void enQueue(const char x) ;

看出不同没？一个参数是引用类型，一个是传值。改成一样就可以了。

补充：
tmp是Node*类型，但是deQueue()返回的是char类型，两种类型不匹配，所以出错了。

#ifndef _binarytree_h
#define _binarytree_h

#include

class queue
{ public:
virtual bool isEmpty() = 0;
virtual void enQueue(const char &x) = 0;
virtual char deQueue() = 0;
virtual char getHead() = 0;
virtual ~queue() {}
};

class linkQueue: public queue
{ private:
struct node {
char data;
node *next;
node(const char &x, node *N = NULL)
{ data = x; next = N;}
node():next(NULL) {}
~node() {}
};
node *front, *rear;

public:
linkQueue() { front = rear = NULL; }

~linkQueue();
bool isEmpty() {return front == NULL;}
void enQueue(const char x) ; //少& -->const char &x
char deQueue() ;

char getHead() {return front->data;}

};
linkQueue::~linkQueue() {
node *tmp;
while (front != NULL) {
tmp = front;
front = front->next;
delete tmp;
}
}

void linkQueue::enQueue(const char x) //少& (const char &x)
{ if (rear == NULL)
front = rear = new node(x);
else {
rear->next = new node(x);
rear = rear->next;
}
}

char linkQueue::deQueue() {
node *tmp = front;
char value = front->data;
front = front->next;
if (front == NULL) rear = NULL;
delete tmp;
return value;
}

class BinaryTree {
……
……
void createTree(char flag)
{ linkQueue que;
Node *tmp;
char x, ldata, rdata;

cout << "\nêäèë¸ù½áμã￡o";
cin >> x;
root = new Node(x);
que.enQueue(root->data);
while (!que.isEmpty()) {
tmp = que.deQueue();
cout << "\nêäèë" << tmp->data
<< "μÄὸö¶ù×ó(" << flag
<< "±í꾿սáμã)￡o";
cin >> ldata >> rdata;
if (ldata != flag)
que.enQueue(tmp->left = new Node(ldata));
if (rdata != flag)
que.enQueue(tmp->right = new Node(rdata));
}
cout << "create completed!\n";
}

#endif