ALLOCA(3) Library Functions Manual ALLOCA(3)

alloca — memory allocator

#include <alloca.h> or

#include <stdlib.h>

void *
alloca(size_t size);

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

alloca() returns a pointer to the beginning of the allocated space.

brk(2), calloc(3), getpagesize(3), malloc(3), realloc(3)

alloca() appeared in Version 7 AT&T UNIX/32V.

alloca() is machine and compiler dependent; its use is discouraged.

alloca() 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.

The use of C99 variable-length arrays and alloca() in the same function will cause the lifetime of alloca's storage to be limited to the block containing the alloca()

September 5, 2006 macOS 15.2