implementing alloca actually requires compiler assistance. A few people here are saying it’s as easy as: sub esp, <size> which is unfortunately only half of the picture. Yes that would “allocate space on the stack” but there are a couple of gotchas. if the compiler had emitted code which references other variables relative to esp … Read more
alloc() is not a standard C library function. Some older compilers and libraries contain an <alloc.h> library which provides some memory allocation functions, but this is not standard. The Microsoft Visual C++ runtime includes an Alloc() function which is somewhat similar to malloc(), but this is also not part of the C standard. malloc() allocates … Read more
Yes, alloca is functionally equivalent to a local variable length array, i.e. this: int arr[n]; and this: int *arr = alloca(n * sizeof(int)); both allocate space for n elements of type int on the stack. The only differences between arr in each case is that 1) one is an actual array and the other is … Read more
The answer is right there in the man page (at least on Linux): RETURN VALUE The alloca() function returns a pointer to the beginning of the allocated space. If the allocation causes stack overflow, program behaviour is undefined. Which isn’t to say it should never be used. One of the OSS projects I work on … Read more