The iterator of vector and map fails.

1. Vector

# Include <iostream> # include <string> # include <vector> using namespace STD; void vectortest () {vector <int> container; For (INT I = 0; I <10; I ++) {container. push_back (I);} vector <int>: iterator ITER; For (iter = container. begin (); iter! = Container. End (); ITER ++) // cycle 2 {container. Erase (ITER) ;}for (iter = container. Begin (); iter! = Container. end (); ITER ++) {cout <* ITER <Endl ;}} int main (INT argc, const char * argv []) {vectortest (); return 0 ;}

Execution result: 0 1 2 3 5 7 9

When deleting an element in a vector, the following elements are moved forward by one place, so the original iterators are invalid.

After deleting the first number 4 greater than 3: 0 1 2 3 5 6 7 8 9

---> But now the iterator points to 5, ITER ++ points to 6 again, and 5 is missing... As a result, 5, 7, and 9 are not deleted.

Method of modification: In loop 2:

     for (iter = container.begin(); iter != container.end();)    {         if(*iter > 3)               {             container.erase(iter);            continue;         }         iter++;    }

Or:

For (iter = container. Begin (); iter! = Container. end ();) {If (* ITER> 3) {iter = container. erase (ITER); // at this time, the location of the ITER is not changed, but the content to be pointed to becomes a continue behind the original element;} ITER ++ ;}

2. Map failure

Map is an associated container that organizes data with a red/black tree or a balanced binary tree. Although an element is deleted, the entire tree is adjusted to conform to the rules of the red/black tree or binary tree, however, the address of a single node in the memory remains unchanged, and the pointing relationship between nodes is changed.

Http://blog.163.com/?email protected]/blog/static/1322296552010824114547940/

The deletion of red and black trees in http://blog.csdn.net/v_july_v/article/details/6105630 is complicated.

Sequent container: (vector, list, And deque)
The erase iterator not only invalidates the iterator pointing to the deleted element, but also invalidates all iterators after the deleted element. Therefore, the erase (ITER ++) method cannot be used, however, the returned value of erase is the next effective iterator.

So the correct method is ::
For (iter = C. Begin (); iter! = C. End ();)
Iter = C. Erase (ITER );
 
Associated containers: (MAP and set are commonly used)
The erase iterator is invalid only for the iterator whose elements are deleted, but the returned value is void. Therefore, erase (ITER ++) is used to delete the iterator,
So the correct method is ::
For (iter = C. Begin (); iter! = C. End ();)
C. Erase (ITER ++ );

TIPS:
In fact, both methods of list can work normally.

STL containers can delete elements by using the erase (key) method in addition to the iterator.
Size_t rm_num = obj. Erase (key );
Rm_num indicates the number of Members who delete the key. In map, the key is the key value, and in other containers, the key is a value.

 

Zookeeper

The iterator of vector and map fails.