alloca(3) [freebsd man page]

ALLOCA(3)						   BSD 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.

SEE ALSO

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

HISTORY

     The alloca() function appeared in Version 32V AT&T UNIX.

BUGS

     The alloca() function is machine and compiler 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 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.

BSD
								 September 5, 2006							       BSD

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)