redhat man page for alloca

ALLOCA(3)						     Linux Programmer's Manual							 ALLOCA(3)

NAME
       alloca - memory allocator

SYNOPSIS
       #include <alloca.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 when the
       function that called alloca returns to its caller.

RETURN VALUE
       The alloca function returns a pointer to the beginning of the allocated space.  If the allocation causes stack overflow, program  behaviour
       is undefined.

CONFORMING TO
       There is evidence that the alloca function appeared in 32v, pwb, pwb.2, 3bsd, and 4bsd.	There is a man page for it in BSD 4.3.	Linux uses
       the GNU version.  This function is not in POSIX or SUSv3.

NOTES ON THE GNU VERSION
       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.

BUGS
       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.

SEE ALSO
       brk(2), pagesize(2), calloc(3), malloc(3), realloc(3)

GNU
								    2002-07-17								 ALLOCA(3)