Iterator, const_iterator and const iterator

Vector is only one type of container. All the standard library containers define the corresponding iterator type. The iterator applies to all containers. Modern C ++ programs prefer to use the iterator instead of subscript operations to access container elements.
1. iterator, const_iterator: traverses elements in the container and accesses the values of these elements. Iterator can change the element value, but const_iterator cannot. The pointer is a bit like the pointer of C.
(Containers can + ITER, while vector can also ITER-N, ITER + n, n is an integer, iter1-iter2: The result is difference_type, the distance between the two elements of the table .)

2. The const_iterator object can be used for const vector or non-const vector. its own value can be changed (it can point to other elements), but it cannot rewrite the element value it points.

Example:

Const vector <int> nines (); // The element value in nines cannot be changed.

Const vecotr <int>: iterator cit2 = nines. Begin (); // error: it will cause changes to the value of the element it points to, while nines is a constant

Vector <int>: const_iterator it = nines. Begin (); // correct: Because the element value is not changed

* It = 10; // error: * It is a const.

+ + It; // correct: it can be changed because it is not a const.

 

3. Const iterator is different from const_iterator: It must be initialized when a const iterator is declared. Once initialized, it cannot be changed. Once initialized, it can only be used

Instead of directing it to other elements. (Therefore, const iterator is useless)

Example: vector Nums (10); // Nums is nonconst
Const vector: iterator CIT = nums. Begin ();
* CIT = 1; // OK: CIT can change its underlying element
++ Cit; // error: Can't change the value of CIT

 

 

From http://www.cnblogs.com/newgreen/archive/2010/08/03/1791583.html