STL: Standard Template Library in C++

To understand Standard Template Library you must know about the C++ Templates.


What is STL?

The C++ STL (Standard Template Library) is a powerful set of C++ template classes to provides general-purpose templatized classes and functions that implement many popular and commonly used algorithms and data structures like vectors, lists, queues, and stacks.

At the core of the Standard Template Library in C++ are following three well-structured components:

ContainersContainers are used to manage collections of objects of a certain kind. There are several different types of containers like deque, list, vector, map etc.
AlgorithmsAlgorithms act on containers. They provide the means by which you will perform initialization, sorting, searching, and transforming of the contents of containers.
IteratorsIterators are used to step through the elements of collections of objects. These collections may be containers or subsets of containers.


Let us take the following program demonstrates the vector container (a C++ Standard Template) which is similar to an array with an exception that it automatically handles its own storage requirements in case it grows:


#include <iostream>
#include <vector>
using namespace std;

int main()
   // create a vector to store int
   vector<int> vec;
   int i;

   // display the original size of vec
   cout << "vector size = " << vec.size() << endl;

   // push 5 values into the vector
   for(i = 0; i < 5; i++){

   // display extended size of vec
   cout << "extended vector size = " << vec.size() << endl;

   // access 5 values from the vector
   for(i = 0; i < 5; i++){
      cout << "value of vec [" << i << "] = " << vec[i] << endl;

   // use iterator to access the values
   vector<int>::iterator v = vec.begin();
   while( v != vec.end()) {
      cout << "value of v = " << *v << endl;

   return 0;


vector size = 0
extended vector size = 5
value of vec [0] = 0
value of vec [1] = 1
value of vec [2] = 2
value of vec [3] = 3
value of vec [4] = 4
value of v = 0
value of v = 1
value of v = 2
value of v = 3
value of v = 4


Here are following points to be noted related to various functions we used in the above example:
  • The push_back( ) member function inserts value at the end of the vector, expanding its size as needed.
  • The size( ) function displays the size of the vector.
  • The function begin( ) returns an iterator to the start of the vector.
  • The function end( ) returns an iterator to the end of the vector.


Leave a Reply