alloca(3) - NetBSD Manual Pages

ALLOCA(3)               NetBSD Library Functions Manual              ALLOCA(3)


NAME

     alloca -- memory allocator


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <stdlib.h>

     void *
     alloca(size_t size);


DESCRIPTION

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


RETURN VALUES

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


SEE ALSO

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


CAVEATS

     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 mem-
         ory.  The allocation made may exceed the bounds of the stack, or even
         go further into other objects in memory, and alloca() cannot deter-
         mine 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(7) for a discussion.

NetBSD 6.0                      March 21, 2011                      NetBSD 6.0