ALLOCA(3) Library Functions Manual ALLOCA(3)

alloca — memory allocator

#include <stdlib.h>

void *
alloca(size_t size);

The () 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.

pagesize(1), brk(2), malloc(3)

The alloca() function is 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.

OpenBSD 7.8 January 17, 2015 ALLOCA(3)