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 func-
       tion 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)