Why is the use of alloca() not considered good practice?

Question

alloca() allocates memory on the stack rather than on the heap, as in the case of malloc(). So, when I return from the routine the memory is freed.

Answer 1

All of the other answers are correct. However, if the thing you want to alloc using alloca() is reasonably small, I think that it's a good technique that's faster and more convenient than using malloc() or otherwise.

In other words, alloca( 0x00ffffff ) is dangerous and likely to cause overflow, exactly as much as char hugeArray[ 0x00ffffff ]; is. Be cautious and reasonable and you'll be fine.