Thread: Null Pointer

I believe the reason for NULL to be declared as (void *)0 is two-fold:

1. Allows NULL to be a pointer type so the compiler can tell if the user is using NULL properly (ie. int x = NULL; will produce a warning).
   
2. NULL might not be 0 on some systems, hence the cast from 0 to void * allows the compiler to do any required things to the 0 before continuing.

Originally Posted by MacGyver

I believe the reason for NULL to be declared as (void *)0 is two-fold:

1. Allows NULL to be a pointer type so the compiler can tell if the user is using NULL properly (ie. int x = NULL; will produce a warning).
   
2. NULL might not be 0 on some systems, hence the cast from 0 to void * allows the compiler to do any required things to the 0 before continuing.

And as I pointed out in the other post, the C++ standard actually accepts 0 the same as NULL, but C "requires" the (void *) cast to ensure it's treated as a pointer for the above reasons.

Edit: See also: http://cboard.cprogramming.com/showthread.php?t=105173

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Mats