C++ LANGUAGE CLASS TEMPLATE

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C++ LANGUAGE CLASS TEMPLATE

Class Template 


Just as we can define function templates, we can also define 
class templates. The general form of a generic class declaration 
is shown here: 

template <class type> class class-name { 
. 
. 
. 
} 

Here, type is the placeholder type name, which will be specified 
when a class is instantiated. You can define more than one generic 
data type by using a comma-separated list. 

Following is the example to define class Stack<> and 
implement generic methods to push and pop the elements from the stack: 

#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; 
    }  
}  
If we compile and run above code, this would produce the following result: 
7 
hello 
Exception: Stack<>::pop(): empty stack