2.10: Invalid and NULL Pointers

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Invalid pointers

A pointer should point to a valid address but not necessarily to valid elements (like for arrays). These are called invalid pointers. Uninitialized pointers are also invalid pointers.

int *ptr1;

int arr[10];

int *ptr2 = arr+20;

Here, ptr1 is uninitialized so it becomes an invalid pointer and ptr2 is out of bounds of arr so it also becomes an invalid pointer.
(Note: invalid pointers do not necessarily raise compile errors)

NULL pointers

Additional information on NULL Pointers is available.

Null pointer is a pointer which point nowhere and not just an invalid address.
Following are 2 methods to assign a pointer as NULL;

int *ptr1 = 0;

int *ptr2 = NULL;

Please note that 0 in the above code is used in a pointer context, and it is different from 0 as an integer

Adapted from:
"Pointers in C/C++ with Examples" by Abhirav Kariya, Geeks for Geeks is licensed under CC BY 4.0