alloca — memory allocator
#include <alloca.h>
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 when the function that called
alloca
() returns to its
caller.
The alloca
() function
returns a pointer to the beginning of the allocated space. If
the allocation causes stack overflow, program behaviour is
undefined.
There is evidence that the alloca
() function appeared in 32v, pwb,
pwb.2, 3bsd, and 4bsd. There is a man page for it in 4.3BSD.
Linux uses the GNU version. This function is not in
POSIX.1-2001.
Normally, gcc
translates calls to alloca
()
by inlined code. This is not done when either the
−ansi or the −fno−builtin option is
given. But beware! By default the glibc version of
<stdlib.h>
includes <alloca.h>
and that
contains the line:
# define alloca(size) __builtin_alloca (size)
with messy consequences if one has a private version of this function.
The fact that the code is inlined, means that it is impossible to take the address of this function, or to change its behaviour by linking with a different library.
The inlined code often consists of a single instruction adjusting the stack pointer, and does not check for stack overflow. Thus, there is no NULL error return.
The alloca
() function is
machine and compiler dependent. On many systems its
implementation is buggy. Its use is discouraged.
On many systems alloca
()
cannot be used inside the list of arguments of a function
call, because the stack space reserved by alloca
() would appear on the stack in the
middle of the space for the function arguments.
brk(2), getpagesize(2), calloc(3), malloc(3), realloc(3)
|