Template Classes

Definition

• A class template is used by the compiler to generate the code for a class.
• You determine the class that you want generated by specifying your choice of type for the parameter that appears between the angled brackets in the template. Doing this generates a particular class called the **instance"" of the class template.

Implementing a class template

A class template is like a regular class definition, except it is prefixed by the keyword template.

Example 1: Class template for a stack.

template <class T>
class Stack
{
public:
    Stack(int = 10) ; 
    ~Stack() { delete [] stackPtr ; }
    int push(const T&); 
    int pop(T&) ;  
    int isEmpty()const { return top == -1 ; } 
    int isFull() const { return top == size - 1 ; } 
private:
    int size ;  // number of elements on Stack.
    int top ;  
    T* stackPtr ;  
} ;

Example 2

#include <iostream>
using std::cout;
using std::endl;
 
template <class T> // to indicate that you are defining a template rather than a class
class Samples
{
public:
    Samples(const T values[], int count);
    Samples(const T& value);
    Samples() {m_Free = 0;}
 
    bool add(const T& value); // insert a value
    T max() const; // calculate maximum
 
private:
    T m_Values[100]; // array to store samples
    int m_Free; // index of free location in m_Values
};
 
template<class T> Samples<T>::Samples(const T& value)
{
    m_Values[0] = value;
    m_Free = 1; //next is free
}
template<class T> Samples<T>::Samples(const T values[], int count)
{
    m_Free = count < 100 ? count:100; // don't exceed the array
    for(int i = 0; i < m_Free; i++)
        m_Values[i] = values[i]; //store count number of samples
}
 
//function to add a sample
template<class T> bool Samples<T>::add(const T& value)
{
    bool OK = m_Free < 100; //indicates there is a free place
    if (OK)
        m_Values[m_Free++] = value; // ok true, so store the value
    return OK;
}
 
//function to obtain maximum sample
template<class T> T Samples<T>::max() const
{
    T theMax = m_Free ? m_Values[0] : 0; // set first sample or 0 as max
 
    for(int i = 1; i < m_Free; i++)
        if(m_Values[i] > theMax)
            theMax = m_Values[i];
    return theMax;
}
 
int main()
{
    double values[5] = {8.1, 1.3, 4.2, 3.4, 1.8};
    Samples<double> myDoubles(values,5);
    cout << "The max is " << myDoubles.max() << endl;
    getchar();
 
}