C++类模板

#include <iostream>
#include <vector>
#include <cstdlib>
#include <string>
#include <stdexcept>

using namespace std;

template <class T>
class Stack { 
   private: 
      vector<T> elems;           // elements 

   public: 
      void push(T const&);      // push element 
      void pop();              // pop element 
      T top() const;          // return top element 

      bool empty() const {    // return true if empty.
         return elems.empty(); 
      } 
}; 

template <class T>
void Stack<T>::push (T const& elem) { 
   // append copy of passed element 
   elems.push_back(elem);    
} 

template <class T>
void Stack<T>::pop () { 
   if (elems.empty()) { 
      throw out_of_range(Stack<>::pop(): empty stack); 
   }

   // remove last element 
   elems.pop_back();         
} 

template <class T>
T Stack<T>::top () const { 
   if (elems.empty()) { 
      throw out_of_range(Stack<>::top(): empty stack); 
   }

   // return copy of last element 
   return elems.back();      
} 

int main() { 
   try {
      Stack<int>         intStack;  // stack of ints 
      Stack<string> stringStack;    // stack of strings 

      // manipulate int stack 
      intStack.push(7); 
      cout << intStack.top() <<endl; 

      // manipulate string stack 
      stringStack.push(hello); 
      cout << stringStack.top() << std::endl; 
      stringStack.pop(); 
      stringStack.pop(); 
   } catch (exception const& ex) { 
      cerr << Exception:  << ex.what() <<endl; 
      return -1;
   } 
}