Iterator and const_iterator

All the standard library containers define the corresponding iterator type. The iterator applies to all containers. Modern C ++ProgramIt is more inclined to use 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 to C is a bit like

(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.

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 <int> Nums (10); // Nums is nonconst

Const vector <int >:: iterator CIT = nums. Begin ();

* CIT = 1; // OK: CIT can change its underlying element

++ Cit; // error: Can't change the value of CIT

For example, read a piece of text into a vector object. Each word is stored as an element in the vector. Converts each word in a vector object to a lowercase letter. Output the converted elements in a vector object. Every eight words are output in one row.

ClassYou must use

Const_iterator; otherwise, it cannot be compiled.