堆栈模板

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#include<iostream>#include<string>#include<cassert>using namespace std;template <class T>class Stack{public:enum {DefaultStack=50,EmptyStack=-1};Stack();                                        //构造函数Stack ( int );                                            //重载构造函数~Stack();                                     //析构函数void push( const T &);T pop();T topNoPop() const;bool empty() const;bool full() const;private:T* elements;int top;int size;void allocate(){elements =new T[size];top=EmptyStack;}void msg(const char* m) const{cout<<" *** "<<m<<" *** "<<endl;}friend ostream& operator<<(ostream&,const Stack<T>&);//友元函数};template<class T>Stack<T>::Stack(){size=DefaultStack;allocate();}template<class T>Stack<T>::Stack(int s){if(s<0)s*=-1;else if(0==s)s=DefaultStack;size=s;allocate();}template <class T>Stack<T>::~Stack(){delete [] elements;}template <class T>void Stack<T>::push(const T &e){    assert(!full());if(!full())elements[++top]=e;elsemsg("Stack full!");}template <class T>T Stack<T>::pop(){assert(!empty());if(!empty())return elements[top--];else{msg("Stack empty!");T dummy_value;return dummy_value;  //return arbitrary value}}template <class T>T Stack<T>::topNoPop() const{assert(top>EmptyStack);if(!empty())return elements[top];else{msg("Stack empty!");T dummy_value;return dummy_value;}}template <class T>bool Stack<T>::empty() const{return top<=EmptyStack;}template <class T>bool Stack<T>::full() const{return top+1>=size;}template <class T>ostream& operator<<(ostream& os,const Stack<T>& s)// 友元函数  重载运算符"<<"{s.msg("Stack contents:");int t=s.top;while(t>s.EmptyStack)cout<<s.elements[t--]<<endl;return os;}int main(){Stack<int> i_stack(4);int a;int i=0;while(i++<4){cin>>a;i_stack.push(a);}    cout<<i_stack.pop();    //弹出栈顶元素cout<<i_stack.topNoPop();  return 0;}
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