c - Using realloc to shrink the allocated memory

Question

Simple question about the realloc function in C: If I use realloc to shrink the memory block that a pointer is pointing to, does the "extra" memory get freed? Or does it need to be freed manually somehow?

For example, if I do

int *myPointer = malloc(100*sizeof(int));
myPointer = realloc(myPointer,50*sizeof(int));
free(myPointer);

Will I have a memory leak?

Answer 1

No, you won't have a memory leak. realloc will simply mark the rest "available" for future malloc operations.

But you still have to free myPointer later on. As an aside, if you use 0 as the size in realloc, it will have the same effect as free on some implementations. As Steve Jessop and R.. said in the comments, you shouldn't rely on it.