Alloca implementation

Question

How does one implement alloca() using inline x86 assembler in languages like D, C, and C++? I want to create a slightly modified version of it, but first I need to know how

Answer 1

If you can't use c99's Variable Length Arrays, you can use a compound literal cast to a void pointer.

#define ALLOCA(sz) ((void*)((char[sz]){0}))

This also works for -ansi (as a gcc extension) and even when it is a function argument;

some_func(&useful_return, ALLOCA(sizeof(struct useless_return)));

The downside is that when compiled as c++, g++>4.6 will give you an error: taking address of temporary array ... clang and icc don't complain though