Proper usage of realloc()

Question

From man realloc:The realloc() function returns a pointer to the newly allocated memory, which is suitably aligned for any kind of variable and may be different from ptr, or NULL if the request fails.

So in this code snippet:

ptr = (int *) malloc(sizeof(int)); ptr1 = (int *) realloc(ptr, count * sizeof(int)); if(ptr1 == NULL){           //reallocated pointer ptr1     printf("Exiting!!\n");     free(ptr);     exit(0); }else{     free(ptr);          //to deallocate the previous memory block pointed by ptr so as not to leave orphaned blocks of memory when ptr=ptr1 executes and ptr moves on to another block     ptr = ptr1;         //deallocation using free has been done assuming that ptr and ptr1 do not point to the same address                      } 

Is it sufficient to just assume that the reallocated pointer points to a different block of memeory and not to the same block.Because if the assumption becomes false and realloc returns the address of the original memory block pointed to by ptr and then free(ptr) executes(for the reason given in the comments) then the memory block would be erased and the program would go nuts. Should I put in another condition which will compare the equality of ptr and ptr1 and exclude the execution of the free(ptr) statement?

Answer 1

Just don't call free() on your original ptr in the happy path. Essentially realloc() has done that for you.

ptr = malloc(sizeof(int)); ptr1 = realloc(ptr, count * sizeof(int)); if (ptr1 == NULL) // reallocated pointer ptr1 {            printf("\nExiting!!");     free(ptr);     exit(0); } else {     ptr = ptr1;           // the reallocation succeeded, we can overwrite our original pointer now }