Iterators in STL
Introduction :
What are iterators?
• Iterators act like pointers and are used to access elements of the container.
• We use iterators to move through the contents of containers.
• Iterators are handled just like pointers.
• We can increment or decrement them as per our requirements.
• Iterators connect containers with algorithms and play a vital role in the manipulation of data
stored in the containers.
• They are often used to pass through from one element to another, this process is called iterating
through the container.
• There are five types of iterators:
➢ Input
➢ Output
➢ Forward
➢ Bidirectional
➢ Random
• Different types of iterators must be used with the different types of containers such
that only sequence and associative containers are allowed to travel through
iterators.
• Each type of iterators is used for performing certain functions.
• The input and output iterators support the least functions.
• They can be used only to pass through in a container.
• The forward iterators support all operations of input and output iterators and also
retain its position in the container.
• A Bidirectional iterator, while supporting all forward iterators operations, provides
the ability to move in the backward direction in the container.
Iterator implementation in Vectors :
#include <iostream>
#include <vector>
using namespace std;
int main() {
vector<int> vec;
int i;
for(i = 0; i < 5; i++) {
vec.push_back(i);
}
// 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;
v++;
}
return 0;
}
Iterator implementation in Map:
/ Create a map and insert some values
std::map<char,int> mymap;
mymap[‘b’] = 100;
mymap[‘a’] = 200;
mymap[‘c’] = 300;
// Iterate over all tuples
for (std::map<char,int>::iterator it = mymap.begin(); it != mymap.end(); ++it)
std::cout << it->first << “ => “ << it->second << ‘\n’;
Iterator implementation in Multimap:
// multimap::begin/end
#include <iostream>
#include <map>
int main ()
{
std::multimap<char,int> mymultimap;
mymultimap.insert (std::pair<char,int>(‘a’,10));
mymultimap.insert (std::pair<char,int>(‘b’,20));
mymultimap.insert (std::pair<char,int>(‘b’,150));
// show content:
for (std::multimap<char,int>::iterator it=mymultimap.begin(); it!=mymultimap.end(); ++it)
std::cout << (*it).first << “ => “ << (*it).second << ‘\n’;
return 0;
}
These are a few examples of the implementation of iterators.
Thanks for reading !!!
