Is realloc guaranteed to be in-place when the buffer is shrinking?

Question

Are there any guarantees that realloc() will always shrink a buffer in-place?? So that the following:

new_ptr = (data_type *) realloc(old_ptr, new_size * siz         


        

Answer 1

Some allocators use a "bucketizing" strategy where allocations sized from, say, 2^3 through 2^4, go to the same allocation bucket. This tends to prevent extreme cases of memory fragmentation where many small allocations spread across the heap prevent large allocations from succeeding. Obviously, in such a heap manager, reducing the size of an allocation could force it to a different bucket.