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

As noted in this newsgroup posting, there are a few reasons why using alloca can be considered difficult and dangerous:

• Not all compilers support alloca.
• Some compilers interpret the intended behaviour of alloca differently, so portability is not guaranteed even between compilers that support it.
• Some implementations are buggy.