Haha you made me laugh :-) In all seriousness, your code isn't "not-brilliant" because of how you did it. It is problematic because of the fact that global buffers are just plain messy. Simply put your code is quite excellent except that it requires the caller to do stuff to clean up after each and every call to the function. And the function is slower because of the fact that it must allocate buffers each and every call (well, probably not, malloc may be over-allocating).
Its better to do malloc(1000) than malloc(1) and incrementally increase the buffer size. What you can do is have a factor to increase your malloc by and just allocate chunks at a time.
