Can I check if a pointer was allocated by malloc/calloc/realloc? [duplicate]

Answer 1

No way to check, you ought to NULL initialize and then test whether NULL indeed

From section 7.20.3.2 The free function of C99 standard:

The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by the calloc, malloc, or realloc function, or if the space has been deallocated by a call to free or realloc, the behavior is undefined.

Answer 2

No, you can't.

Basically, you should not need to do this. If you are wanting to write a helper function to free some memory given a pointer, than you should awarely and explicitely pass a dynamically allocated pointer to a certain area of memory to do so.

Raw pointers in C cannot transport extra informations about the memory they are pointing to. If you want to have such informations, you will have to pass an additional wrapper that holds the pointer you are interested in, such as :

typedef struct my_pointer
{
   void  *ptr;
   int   is_dynamically_allocated;
}  ptr;

But this would be a huge loss of memory/time.