Iterator in C ++

Containers in C ++

Standard sequence container: vector, String, deque, list

Standard associated containers: Set, Multiset, map, and multimap

 

Iterator Classification

Based on the operations supported by the iterator, The iterator can be divided into five categories.

1. Input iterator: it is a read-only iterator and can only be read once at each traversal location.

2. Output iterator: it is a write-only iterator that can only be written once at each traversal position.

3. Forward iterator: it provides both input and output iterators, but it can read and write repeatedly at the same position. But it does not support operator --, so it can only move forward.

4. Bidirectional iterator: similar to the forward iterator, it is easy to move backward and forward.

5. Random Access iterator: all functions of the two-way iterator are available. In addition, it provides an iterator for arithmetic, that is, any position that can jump forward or backward in one step.

 

The iterator provided in the C ++ container

1. The input and output iterator models are based on read/write operations on input and output streams (such as files. It is easy to understand that the most common manifestations of the input and output iterators are istream_iterator and ostream_iterator.

2. All standard STL containers support more powerful iterators than the forward iterator. (Except for one-way linked list containers of hash containers, which provide forward iterators)

3. Standard associated containers provide two-way iterators. This is also true for list.

4. vector, string, and deque all provide random access iterators. The internal pointer to the array is also a random access iterator for the array.

 

Istream_iterator and ostream_iterator usage example

Istream_iterator

1 // Istream_iterator example
2 # Include < Iostream >
3 # Include < Iterator >
4 Using   Namespace STD;
5
6 Int Main (){
7 Double Value1, value2;
8 Cout <   " Please, insert two values: " ;
9
10 Istream_iterator < Double > EOS; // End-of-stream iterator
11 Istream_iterator < Double > Iit (CIN ); // Stdin iterator
12
13 If (IIT ! = EOS) value1 = * Iit;
14
15 Iit ++ ;
16 If (IIT ! = EOS) value2 = * Iit;
17
18 Cout < Value1 <   " * "   < Value2 <   " = "   < (Value1 * Value2) < Endl;
19
20 Return   0 ;
21 }
22

 

Output:

Please, insert two values: 2 322*32 = 64

Ostream_iterator

1 // Ostream_iterator example
2 # Include < Iostream >
3 # Include < Iterator >
4 # Include < Vector >
5 Using   Namespace STD;
6
7 Int Main (){
8 Vector < Int > Myvector;
9 For ( Int I = 1 ; I < 10 ; ++ I) myvector. push_back (I * 10 );
10
11 Ostream_iterator < Int > Out_it (cout, " , " );
12 Copy (myvector. Begin (), myvector. End (), out_it );
13 Return   0 ;
14 }
15

 

Output:

10, 20, 30, 40, 50, 60, 70, 80, 90,