Why doesn't free(p) set p to NULL?

Question

Any reasons why this can not be standard behavior of free()?

multiple pointers pointing to the same object:

#include 
#i         


        

Answer 1

C function parameters are always passed by value, so in order to modify the pointer passed to free() you would need to pass a pointer to the pointer being deallocated, which can lead bugs caused by forgotten & operators.

Secondly, if that pointer had any aliases, the programmer would still be responsible for nulling them out. I could see problems caused by programmers assuming that all references were set to NULL.

Finally, it's not always necessary to set the pointer to NULL. Imagine a function which allocates some memory, does some work and frees it before returning. I could see how setting the pointer to NULL might not seem optimal.