I've got the following faulty piece of code in C and I am wondering if there will be a memory leak or if there will be a pointer which is pointing to a free memory location.
int* p = (int*) malloc(sizeof(int)); p = NULL; free(p); 
2 Answers
Yes it will leak memory. You assign p to NULL before freeing the contents it's pointing to. One quick change will fix it:
int* p = malloc(sizeof(int)); free(p); p = NULL; The difference here is we give free the address allocated by malloc before setting p to NULL. In general setting a pointer to NULL will not free the contents, but will allow you to check if the pointer is valid or not which can have a lot of practical applications.
2 Comments
CoffeeTableEspresso
you don't need to cast
malloc, this is C.
Dom
I just copied their code. I'll do some other cleanup and remove it.
You will have a memory leak.
After you assign NULL to p, you no longer have a way to refer to the memory you allocated with malloc.
Your call to free will try to free NULL, doing nothing.
The following will correctly free the memory:
int *p = malloc(sizeof(int)); free(p); p = NULL; Note that you don't need to set p to NULL after freeing, you only really need the first two lines.
answered Feb 10, 2020 at 20:27
CoffeeTableEspresso
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pis no longer pointing to the allocated memory chunk (and neither is anything else), so you cannot free it.malloc.