The realloc implementation in this blog is incorrect: the passed in pointer must not be freed if realloc is called with a non-zero length and returns NULL. This will cause a double free in correct callers.
As someone else pointed out, the example call of realloc is also incorrect.
edit: also, malloc is incorrect for three reasons: 1) sbrk doesn't return NULL on failure, 2) a large size_t length will cause a contraction in the heap segment rather than an allocation, and 3) sbrk doesn't return a pointer aligned in any particular way, whereas malloc must return a pointer suitably aligned for all types.
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The realloc implementation in this blog is incorrect: the passed in pointer must not be freed if realloc is called with a non-zero length and returns NULL. This will cause a double free in correct callers.
As someone else pointed out, the example call of realloc is also incorrect.
edit: also, malloc is incorrect for three reasons: 1) sbrk doesn't return NULL on failure, 2) a large size_t length will cause a contraction in the heap segment rather than an allocation, and 3) sbrk doesn't return a pointer aligned in any particular way, whereas malloc must return a pointer suitably aligned for all types.
I fixed the double free. I must admit that the code was typed as I wrote the blog entry, and is horribly wrong :)