May 3, 2010 ALLOCA 3

alloca - memory allocator

Standard C Library (libc, -lc)

void * alloca(size_t size)

The alloca() function allocates size bytes of space in the stack frame of the caller. This temporary space is automatically freed on return.

The alloca() function returns a pointer to the beginning of the allocated space. If the allocation failed, a NULL pointer is returned.

Few limitations can be mentioned:

The alloca() function is machine dependent; its use is discouraged.
The alloca() function is slightly unsafe because it cannot ensure that the pointer returned points to a valid and usable block of memory. The allocation made may exceed the bounds of the stack, or even go further into other objects in memory, and alloca() cannot determine such an error. Avoid alloca() with large unbounded allocations.
Since alloca() modifies the stack at runtime, it causes problems to certain security features. See security(8) for a discussion.