realloc changes the size of an existing dynamically allocated storage instance. It receives the existing pointer and a requested byte size, then returns either a pointer to storage of the new size or null. section 13.1.1 section 13.1
TAKEAWAY: resizing changes pointer validity and preserves only the applicable prefix.
- The returned pointer may equal the argument or identify a relocated object; do not continue using pointers derived from the original object. section 13.1.1
- Enlarging preserves the original-sized prefix, while shrinking preserves the prefix that fits the new size. section 13.1.1
- Check the return value before replacing the stored pointer; the circular-buffer implementation returns failure when resizing cannot be fulfilled. section 13.1.1
- Treat realloc as both deallocation of the old object and allocation of the new one when tracking allocation and free pairs. section 13.1.2
Growing a circular buffer
A circular buffer can resize its backing array with `ntab = realloc(c->tab, sizeof(double[nlen]));`. After checking `ntab`, the implementation handles data that wraps across the old array boundary: it copies one chunk upward with `memcpy` or moves the other chunk with `memmove`, then stores the new capacity, start position, length, and table pointer in the structure. section 13.1.1
Only pass allocation pointers, including a pointer returned by realloc, to free; never free a pointer into the middle or a smaller part of an allocated object, or reuse a pointer after it has been freed. section 13.1.2
