C++ Iterators

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Iterators are used to access the individual elements in a container.

An iterator can be classified in the following ways:

  • Bidirectional Iterator
  • Forward Iterator
  • Input Iterator
  • Output Iterator
  • Random Access Iterator

Syntax:

 <ContainerType>:: iterator; 
#include <iostream> 
#include<iterator>  
#include<list>
using namespace std;  

int main()  
{  
   list<int> l={4,3,2,1};  
   list<int>::iterator it=l.begin();  
   l.insert(it,5);
   it=l.begin();  
   while(it!=l.end()) 
   { 
		cout << *it;  
		++it;
   }
   return 0;  
}
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Bidirectional Iterator

Bidirectional iterator is used to access the elements in both the directions.

Bidirectional iterator such as list, set, map, and etc.

Example:

 #include <iostream> 
#include<iterator>  
#include<list>
using namespace std;  

int main()  
{  
   list<int> l={4,3,2,1};  
   list<int>::iterator it=l.begin();
   list<int>::reverse_iterator rit=l.rbegin();   
   while(it!=l.end()) 
   { 
		cout << *it << " ";  
		++it;
   }
   cout << endl;
   while(rit!=l.rend()) 
   { 
		cout << *rit << " "; 
		rit++;
   }
   return 0;  
}
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Forward Iterator

Forward iterator helps to read the contents from the beginning to the end of a container.

Input Iterator

Input Iterator is used to read the values from the container.

Example:

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

int main()  
{  
	vector<int> v{1,2,3,4,5};  
    vector<int>::iterator it,it1;  
    it=v.begin();  
    it1=v.begin()+2;  
    if(it==it1)
    { 
    	cout << "Both the iterators are equal" << endl;
	}  
    else{  
    	cout << "Both the iterators are not equal" << endl; 
    } 
    return 0;  
}
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Output Iterator

Output Iterator is used to modify the value in the container.

Example:

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

int main()  
{  
   list<int> l={4,3,2,1};  
   list<int>::iterator it=l.begin();  
   l.insert(it,5);
   it=l.begin();  
   while(it!=l.end()) 
   { 
		cout << *it;  
		++it;
   }
   return 0;  
}
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