checking for NULL before calling free

c allocation
zaharpopov picture zaharpopov · Dec 16, 2009 · Viewed 12.9k times · Source

Many C code freeing pointers calls:

if (p)
  free(p);

But why? I thought C standard say the free function doesn't do anything given a NULL pointer. So why another explicit check?

Answer

anon picture anon · Dec 16, 2009

The construct:

free(NULL);

has always been OK in C, back to the original UNIX compiler written by Dennis Ritchie. Pre-standardisation, some poor compilers might not have fielded it correctly, but these days any compiler that does not cannot legitimately call itself a compiler for the C language. Using it typically leads to clearer, more maintainable code.

Related questions

Why is the use of alloca() not considered good practice?

alloca() allocates memory on the stack rather than on the heap, as in the case of malloc(). So, when I return from the routine the memory is freed. So, actually this solves my problem of freeing up dynamically allocated memory. …

Read More
Determine size of dynamically allocated memory in C

Is there a way in C to find out the size of dynamically allocated memory? For example, after char* p = malloc (100); Is there a way to find out the size of memory associated with p?

Read More
malloc(sizeof(int)) vs malloc(sizeof(int *)) vs (int *)malloc(sizeof(int))

I acknowledge that all three of these have a different meaning. But, I don't understand on what particular instances would each of these apply. Can anyone share an example for each of these? Thank you. malloc(sizeof(int)) malloc(sizeof(…

Read More