| 1 | /* obstack.h - object stack macros
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| 2 | Copyright 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1996, 1997, 1998,
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| 3 | 1999, 2000
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| 4 | Free Software Foundation, Inc.
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| 5 |
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| 6 |
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| 7 | NOTE: The canonical source of this file is maintained with the GNU C Library.
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| 8 | Bugs can be reported to [email protected].
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| 9 |
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| 10 | This program is free software; you can redistribute it and/or modify it
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| 11 | under the terms of the GNU General Public License as published by the
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| 12 | Free Software Foundation; either version 2, or (at your option) any
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| 13 | later version.
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| 14 |
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| 15 | This program is distributed in the hope that it will be useful,
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| 16 | but WITHOUT ANY WARRANTY; without even the implied warranty of
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| 17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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| 18 | GNU General Public License for more details.
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| 19 |
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| 20 | You should have received a copy of the GNU General Public License
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| 21 | along with this program; if not, write to the Free Software
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| 22 | Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
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| 23 | USA. */
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| 24 |
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| 25 | /* Summary:
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| 26 |
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| 27 | All the apparent functions defined here are macros. The idea
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| 28 | is that you would use these pre-tested macros to solve a
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| 29 | very specific set of problems, and they would run fast.
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| 30 | Caution: no side-effects in arguments please!! They may be
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| 31 | evaluated MANY times!!
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| 32 |
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| 33 | These macros operate a stack of objects. Each object starts life
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| 34 | small, and may grow to maturity. (Consider building a word syllable
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| 35 | by syllable.) An object can move while it is growing. Once it has
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| 36 | been "finished" it never changes address again. So the "top of the
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| 37 | stack" is typically an immature growing object, while the rest of the
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| 38 | stack is of mature, fixed size and fixed address objects.
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| 39 |
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| 40 | These routines grab large chunks of memory, using a function you
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| 41 | supply, called `obstack_chunk_alloc'. On occasion, they free chunks,
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| 42 | by calling `obstack_chunk_free'. You must define them and declare
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| 43 | them before using any obstack macros.
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| 44 |
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| 45 | Each independent stack is represented by a `struct obstack'.
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| 46 | Each of the obstack macros expects a pointer to such a structure
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| 47 | as the first argument.
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| 48 |
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| 49 | One motivation for this package is the problem of growing char strings
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| 50 | in symbol tables. Unless you are "fascist pig with a read-only mind"
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| 51 | --Gosper's immortal quote from HAKMEM item 154, out of context--you
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| 52 | would not like to put any arbitrary upper limit on the length of your
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| 53 | symbols.
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| 54 |
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| 55 | In practice this often means you will build many short symbols and a
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| 56 | few long symbols. At the time you are reading a symbol you don't know
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| 57 | how long it is. One traditional method is to read a symbol into a
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| 58 | buffer, realloc()ating the buffer every time you try to read a symbol
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| 59 | that is longer than the buffer. This is beaut, but you still will
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| 60 | want to copy the symbol from the buffer to a more permanent
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| 61 | symbol-table entry say about half the time.
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| 62 |
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| 63 | With obstacks, you can work differently. Use one obstack for all symbol
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| 64 | names. As you read a symbol, grow the name in the obstack gradually.
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| 65 | When the name is complete, finalize it. Then, if the symbol exists already,
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| 66 | free the newly read name.
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