1. Null pointer:

  • The name of a null pointer means that the pointer is empty and does not store any memory address.

This corresponds to two keywords,nil and nil. Where nil is a null pointer to the OC object. Nil is a null pointer to a class.

2. Wild pointer

  • Wild pointer to the internal storage a have been released, but hasn’t been rewritten (zombie object), the object’s address before the object is not copying, visit wild pointer, application is possible, but the fast memory addresses are copy, the original object does not exist, this time to visit wild pointer, can not find object, program will collapse.

Zombie objects

  • Zombie object that has been freed, but the memory space has not been overwritten. The current object is still accessible. But the system has been marked free and can be reassigned at any time for replication. The object is not accessible at this point.