Free Implementation Quiz

1. A pointer p was allocated by the teaching allocator, then freed. Another allocation reuses its block. What does writing through the old p risk? Select one.

Select one answer.

Safely restoring the first allocation Corrupting the new owner’s data Automatically extending the heap Only changing a private copy

2. Why is my_free(NULL) handled before computing the preceding header? Select one.

Select one answer.

NULL is a no-op input and has no valid preceding allocation header The header always lives at address zero NULL means free every block Subtracting a header from NULL finds the list head

3. A diagnostic reads a magic value just before any supplied pointer. Does a matching value establish general pointer validity? Select one.

Select one answer.

Yes; a magic value cannot occur in ordinary data Yes; C checks every dereference against allocation bounds No; reading the candidate address itself may already be invalid No; magic values are only useful for stack pointers

4. After freeing an interior block, does this simple flag-based allocator lower the program break? Answer yes or no.

5. Illustrative header size H=24, alignment A=8, current break=4125. A 9-byte allocation is requested. At what address does its payload begin? Answer in decimal.

6. In free-basic, allocate A, free A, then allocate a smaller B. Which behavior belongs to this stage? Select one.

Select one answer.

B must reuse A because a free flag exists The naive allocation path appends B; searching free blocks starts in the next module Free removes A from the block list Free must shrink the program break

7. Heap growth fails while requesting a new block. When may the list gain a new successor? Select one.

Select one answer.

Before growth so the allocator remembers the request After the failure sentinel is converted to a header Only if some previous block is free Only after successful growth and complete header initialization

8. Why reject size > INTPTR_MAX-H-(A-1) before growth? Select one.

Select one answer.

It keeps the full header, worst-case padding, and payload reservation representable before signed conversion It forces every payload to equal H It guarantees all C types have maximal alignment It makes free return storage to the OS