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 allo-
       cated  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	argu-
       ments.

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



GNU				  2002-07-17			    ALLOCA(3)