Iterators are used to access members of the container classes, and can be used in a similar manner to pointers. For example, one might use an iterator to step through the elements of a vector. There are several different types of iterators:
| Iterator | Description |
|---|---|
| input_iterator | Read values with forward movement. These can be incremented, compared, and dereferenced. |
| output_iterator | Write values with forward movement. These can be incremented and dereferenced. |
| forward_iterator | Read or write values with forward movement. These combine the functionality of input and output iterators with the ability to store the iterators value. |
| bidirectional_iterator | Read and write values with forward and backward movement. These are like the forward iterators, but you can increment and decrement them. |
| random_iterator | Read and write values with random access. These are the most powerful iterators, combining the functionality of bidirectional iterators with the ability to do pointer arithmetic and pointer comparisons. |
| reverse_iterator | Either a random iterator or a bidirectional iterator that moves in reverse direction. |
Each of the container classes is associated with a type of iterator, and each of the STL algorithms uses a certain type of iterator. For example, vectors are associated with random-access iterators, which means that they can use algorithms that require random access. Since random-access iterators encompass all of the characteristics of the other iterators, vectors can use algorithms designed for other iterators as well.
The following code creates and uses an iterator with a vector:
vector<int> the_vector;
vector<int>::iterator the_iterator;
for( int i=0; i < 10; i++ )
the_vector.push_back(i);
int total = 0;
the_iterator = the_vector.begin();
while( the_iterator != the_vector.end() ) {
total += *the_iterator;
the_iterator++;
}
cout << "Total=" << total << endl;
Notice that you can access the elements of the container by dereferencing the iterator.