Should I free memory in C if it is not allocated properly?

Question

when declaring for example a malloc and then checking if it is NULL to see if it has been properly allocated, should I free the memory if it is null, example:

int *p;
p = (int *)malloc(sizeof(int)); 
  
    if (p == NULL)
    {
        free(p); //Should I free here or will it create an error?
        return NULL;
    }    

Answer 1

If malloc returns a null pointer it has failed to allocate anything at all, and there's nothing to free.

With that said, passing a null pointer to free does nothing, so it's safe.

On a related note, in C you shouldn't really cast the result of malloc.