GCC Middle and Back End API Reference
obstack-utils.h
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1// Obstack-related utilities.
2// Copyright (C) 2020-2024 Free Software Foundation, Inc.
3//
4// This file is part of GCC.
5//
6// GCC is free software; you can redistribute it and/or modify it under
7// the terms of the GNU General Public License as published by the Free
8// Software Foundation; either version 3, or (at your option) any later
9// version.
10//
11// GCC is distributed in the hope that it will be useful, but WITHOUT ANY
12// WARRANTY; without even the implied warranty of MERCHANTABILITY or
13// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14// for more details.
15//
16// You should have received a copy of the GNU General Public License
17// along with GCC; see the file COPYING3. If not see
18// <http://www.gnu.org/licenses/>.
19
20#ifndef GCC_OBSTACK_UTILS_H
21#define GCC_OBSTACK_UTILS_H
22
23// This RAII class automatically frees memory allocated on an obstack,
24// unless told not to via keep (). It automatically converts to an
25// obstack, so it can (optionally) be used in place of the obstack
26// to make the scoping clearer. For example:
27//
28// obstack_watermark watermark (ob);
29// auto *ptr1 = XOBNEW (watermark, struct1);
30// if (...)
31// // Frees ptr1.
32// return false;
33//
34// auto *ptr2 = XOBNEW (watermark, struct2);
35// if (...)
36// // Frees ptr1 and ptr2.
37// return false;
38//
39// // Retains ptr1 and ptr2.
40// watermark.keep ();
41//
42// auto *ptr3 = XOBNEW (watermark, struct3);
43// if (...)
44// // Frees ptr3.
45// return false;
46//
47// // Retains ptr3 (in addition to ptr1 and ptr2 above).
48// watermark.keep ();
49// return true;
50//
51// The move constructor makes it possible to transfer ownership to a caller:
52//
53// obstack_watermark
54// foo ()
55// {
56// obstack_watermark watermark (ob);
57// ...
58// return watermark;
59// }
60//
61// void
62// bar ()
63// {
64// // Inherit ownership of everything that foo allocated.
65// obstack_watermark watermark = foo ();
66// ...
67// }
69{
70public:
72 constexpr obstack_watermark (obstack_watermark &&) = default;
73 ~obstack_watermark () { obstack_free (m_obstack, m_start); }
74
75 operator obstack *() const { return m_obstack; }
76 void keep () { m_start = XOBNEWVAR (m_obstack, char, 0); }
77
78private:
80
81protected:
83 char *m_start;
84};
85
86#endif
Definition obstack-utils.h:69
void keep()
Definition obstack-utils.h:76
DISABLE_COPY_AND_ASSIGN(obstack_watermark)
obstack_watermark(obstack *ob)
Definition obstack-utils.h:71
obstack * m_obstack
Definition obstack-utils.h:82
constexpr obstack_watermark(obstack_watermark &&)=default
~obstack_watermark()
Definition obstack-utils.h:73
char * m_start
Definition obstack-utils.h:83
static struct obstack obstack
Definition gcc.cc:357