c++ - In which cases is alloca() useful?

Question

Why would you ever want to use alloca() when you could always allocate a fixed size buffer on the stack large enough to fit all uses? This is not a rhetorical question...

Answer 1

It could be useful if the size of the buffer varies at runtime, or if you only sometimes need it: this would use less stack space overall than a fixed-size buffer in each call. Particularly if the function is high up the stack or recursive.