C++ Templates

Templates are the foundation of generic programming which involves writing code in a way that is independent of any particular type.
A template is a blueprint or formula for creating a generic class or a function. The library containers like iterators, and algorithms are examples of generic programming and have been developed using template concept.
There is a single definition of each container, such as vector, but we can define many different kinds of vectors for example, vector or vector .
You can use templates to define functions as well as classes, let us see how do they work:

Function Template:

The general form of a template function definition is shown here:

template ret-type func-name(parameter list) { // body of function }

Here, type is a placeholder name for a data type used by the function. This name can be used within the function definition.
The following is the example of a function template that returns the maximum of two values:

#include #include using namespace std; template inline T const& Max (T const& a, T const& b) { return a < b ? b:a; } int main () { int i = 39; int j = 20; cout << "Max(i, j): " << Max(i, j) << endl; double f1 = 13.5; double f2 = 20.7; cout << "Max(f1, f2): " << Max(f1, f2) << endl; string s1 = "Hello"; string s2 = "World"; cout << "Max(s1, s2): " << Max(s1, s2) << endl; return 0; }

If we compile and run above code, this would produce following result:

Max(i, j): 39 Max(f1, f2): 20.7 Max(s1, s2): World

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 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 
#include 
#include 
#include 
#include 

using namespace std;

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

template 
void Stack::pop () 
{ 
    if (elems.empty()) { 
        throw out_of_range("Stack<>::pop(): empty stack"); 
    }
 // remove last element 
    elems.pop_back();         
} 

template 
T Stack::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         intStack;  // stack of ints 
        Stack stringStack;    // stack of strings 

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