glib/galloca.h

   1 /* GLIB - Library of useful routines for C programming
   2  * Copyright (C) 1995-1997  Peter Mattis, Spencer Kimball and Josh MacDonald
   3  *
   4  * This library is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU Lesser General Public
   6  * License as published by the Free Software Foundation; either
   7  * version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * Lesser General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Lesser General Public
  15  * License along with this library; if not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 /*
  19  * Modified by the GLib Team and others 1997-2000.  See the AUTHORS
  20  * file for a list of people on the GLib Team.  See the ChangeLog
  21  * files for a list of changes.  These files are distributed with
  22  * GLib at ftp://ftp.gtk.org/pub/gtk/.
  23  */
  24
  25 #ifndef __G_ALLOCA_H__
  26 #define __G_ALLOCA_H__
  27
  28 #if !defined (__GLIB_H_INSIDE__) && !defined (GLIB_COMPILATION)
  29 #error "Only <glib.h> can be included directly."
  30 #endif
  31
  32 #include <glib/gtypes.h>
  33
  34 #if defined(__BIONIC__) && defined (GLIB_HAVE_ALLOCA_H)
  35 # include <alloca.h>
  36 #elif defined(__GNUC__)
  37 /* GCC does the right thing */
  38 # undef alloca
  39 # define alloca(size)   __builtin_alloca (size)
  40 #elif defined (GLIB_HAVE_ALLOCA_H)
  41 /* a native and working alloca.h is there */
  42 # include <alloca.h>
  43 #else /* !__GNUC__ && !GLIB_HAVE_ALLOCA_H */
  44 # if defined(_MSC_VER) || defined(__DMC__)
  45 #  include <malloc.h>
  46 #  define alloca _alloca
  47 # else /* !_MSC_VER && !__DMC__ */
  48 #  ifdef _AIX
  49 #   pragma alloca
  50 #  else /* !_AIX */
  51 #   ifndef alloca /* predefined by HP cc +Olibcalls */
  52 G_BEGIN_DECLS
  53 char *alloca ();
  54 G_END_DECLS
  55 #   endif /* !alloca */
  56 #  endif /* !_AIX */
  57 # endif /* !_MSC_VER && !__DMC__ */
  58 #endif /* !__GNUC__ && !GLIB_HAVE_ALLOCA_H */
  59
  60 /**
  61  * g_alloca:
  62  * @size: number of bytes to allocate.
  63  *
  64  * Allocates @size bytes on the stack; these bytes will be freed when the current
  65  * stack frame is cleaned up. This macro essentially just wraps the alloca()
  66  * function present on most UNIX variants.
  67  * Thus it provides the same advantages and pitfalls as alloca():
  68  *
  69  * - alloca() is very fast, as on most systems it's implemented by just adjusting
  70  *   the stack pointer register.
  71  *
  72  * - It doesn't cause any memory fragmentation, within its scope, separate alloca()
  73  *   blocks just build up and are released together at function end.
  74  *
  75  * - Allocation sizes have to fit into the current stack frame. For instance in a
  76  *   threaded environment on Linux, the per-thread stack size is limited to 2 Megabytes,
  77  *   so be sparse with alloca() uses.
  78  *
  79  * - Allocation failure due to insufficient stack space is not indicated with a %NULL
  80  *   return like e.g. with malloc(). Instead, most systems probably handle it the same
  81  *   way as out of stack space situations from infinite function recursion, i.e.
  82  *   with a segmentation fault.
  83  *
  84  * - Special care has to be taken when mixing alloca() with GNU C variable sized arrays.
  85  *   Stack space allocated with alloca() in the same scope as a variable sized array
  86  *   will be freed together with the variable sized array upon exit of that scope, and
  87  *   not upon exit of the enclosing function scope.
  88  *
  89  * Returns: space for @size bytes, allocated on the stack
  90  */
  91 #define g_alloca(size)           alloca (size)
  92 /**
  93  * g_newa:
  94  * @struct_type: Type of memory chunks to be allocated
  95  * @n_structs: Number of chunks to be allocated
  96  *
  97  * Wraps g_alloca() in a more typesafe manner.
  98  *
  99  * Returns: Pointer to stack space for @n_structs chunks of type @struct_type
 100  */
 101 #define g_newa(struct_type, n_structs)  ((struct_type*) g_alloca (sizeof (struct_type) * (gsize) (n_structs)))
 102
 103 #endif /* __G_ALLOCA_H__ */