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<html>
<head>
<title>SWIG Engineering Manual</title>
</head>
<body bgcolor="#ffffff">
<center>
<h1>SWIG Engineering Manual</h1>
<b>David Beazley <br>
Department of Computer Science <br>
University of Chicago <br>
Chicago, IL 60637 <br>
beazley@cs.uchicago.edu <br>
</b>
</center>
<p>
<b>$Header$</b>
<p>
(Note : This is a work in progress.)
<h2>Table of Contents</h2>
<ul>
<li><a name="i1" href="#1">1. Introduction</a>
<li><a name="i2" href="#2">2. Programming Languages and Libraries</a>
<li><a name="i3" href="#3">3. The Source Directory and Module Names</a>
<li><a name="i4" href="#4">4. Include Files</a>
<li><a name="i5" href="#5">5. File Structure</a>
<li><a name="i6" href="#6">6. Bottom-Up Design</a>
<li><a name="i7" href="#7">7. Functions</a>
<li><a name="i8" href="#8">8. Naming Conventions</a>
<li><a name="i9" href="#9">9. Visibility</a>
<li><a name="i10" href="#10">10. Miscellaneous Coding Guidelines</a>
<li><a name="i11" href="#11">11. CVS Tagging Conventions</a>
</ul>
<a name="1" href="#i1">
<h2>1. Introduction</h2>
</a>
The purpose of this document is to describe various coding conventions
and organizational aspects for SWIG developers. The idea for this
document is largely borrowed from John Ousterhout's Tcl/Tk Engineering
Manual. It is not my intent to overly managerial about matters--rather I'm
hoping to make life a little less chaotic for everyone.
<p>
First a little background: SWIG was started in 1995 as a one-person
project and continued in this mode of operation until about 1998.
Most of this development was driven by ideas submitted by early SWIG
users as opposed to being motivated by a grand design. As a result,
the code ended up being a pretty horrible C++ coding disaster. A
mostly working disaster perhaps, but a disaster nonetheless.
<p>
With that said, the primary goal of future SWIG development is to
reengineer the original system, fix most of its inherent design flaws,
and to produce what I hope will become a highly extensible and modular
interface compiler framework. To this do this, there are a few
critical areas of work. First, I want to restructure SWIG as a
collection of loosely coupled modules written in either ANSI C or an
scripting language. Second, I want the system to be minimalistic in
its use of data structures and interconnections. The primary reason
for this is that the fewer data structures there are, the less users
will have to remember. This will also make the system more accessible
to non-experts. Finally, I want to reevaluate the whole idea of a
SWIG module is and expand the definition to include just about
anything from parsers, preprocessors, optimizers, interface editors,
and code generators.
<p>
The rest of this document outlines a few general rules of how code
should be developed within the SWIG project. These rules are
primarily drawn from my own experience developing software and
observing the practices of other successful projects.
<a name="2" href="#i2">
<h2>2. Programming Languages and Libraries </h2>
</a>
All SWIG modules must be written in either ANSI C or one of the
scripting languages for which SWIG can generate an interface (e.g.,
Perl, Python, or Tcl). C++ is currently being used to write
SWIG modules, but it is only being utilized to avoid working with
a lot of pointers to functions. <b>Advanced C++ features like namespaces, templates,
and overloading should not be used.</b>.
<p>
Module writers should make every attempt to use only those functions
described in the POSIX.1 standard. This includes most of the
functions contained the Kernighan and Ritchie C programming book. Use
of operating system dependent functionality such as socket libraries
should always be included inside a conditional compilation block so
that it can be omitted on problematic platforms. If you are unsure
about a library call, check the man page or contact Dave.
<a name="3" href="#i3">
<h2>3. The Source Directory and Module Names</h2>
</a>
All SWIG modules are contained within the "Source" directory. Within
this directory, each module is placed into its own subdirectory. The
name of this subdirectory should exactly match the name of the module.
For example, if you are creating a module called "Tcl", all of your
files should be placed in a directory "Tcl".
<p>
When choosing a module name, please pick a name that is not
currently in use. As a general convention, the first letter of a
module name is capitalized such as "Perl". Alternatives such as
"perl" or "PERL" should be avoided. In certain instances, the first
two letters may be capitalized as in "CParse." The exact usage of
this is somewhat inconsistent and isn't terribly important--just make
sure the first letter is capitalized. Also, module names should not
start with numbers, include underscores or any other special
non-alphanumeric characters.
<a name="4" href="#i4">
<h2>4. Include Files </h2>
</a>
All modules should include a header file that defines the public interface.
The name of this header file should be of the form "swigmodule.h" where
"module" is the name of your module. For example, if you created a
module "Perl", the header file should be named "swigperl.h". This scheme
should prevent header-file naming conflicts both within SWIG and when linking
parts of SWIG to the outside world.
<p>
All header files should include a short description, author information, copyright message,
CVS version, include guards, and be C++ aware. For example:
<blockquote>
<pre>
/* -------------------------------------------------------------------------
* swigperl.h
*
* All of the externally visible functions in the Perl module.
*
* Author(s) : David Beazley (beazley@cs.uchicago.edu)
*
* Copyright (C) 1999-2000, The University of Chicago.
* See the file LICENSE for information on usage and redistribution.
*
* $Header$
* ------------------------------------------------------------------------- */
#ifndef _SWIGPERL_H
#define _SWIGPERL_H 1
#ifdef __cplusplus
extern "C" {
#endif
/* Your declarations here */
...
#ifdef __cplusplus
}
#endif
#endif /* _SWIGPERL_H */
</pre>
</blockquote>
<p>
To minimize compilation time, please include as few other header files as possible.
<a name="5" href="#i5">
<h2>5. File Structure </h2>
</a>
Each file in a module should be given a filename that is all lowercase letters
such as "parser.c", not "Parser.c" or "PARSER.c". Please note that filenames
are case-insensitive on Windows so this convention will prevent you from inadvertantly
creating two files that differ in case-only.
<p>
Each file should include a short abstract, author information, copyright information, and
a CVS revision tag like this:
<blockquote>
<pre>
/* -----------------------------------------------------------------------------
* include.c
*
* This file implements the functions used to locate and include files in
* the SWIG library. Functions for maintaining the library search path are
* also located here.
*
* Author(s) : David Beazley (beazley@cs.uchicago.edu)
*
* Copyright (C) 1999-2000, The University of Chicago.
* See the file LICENSE for information on usage and redistribution.
* ----------------------------------------------------------------------------- */
static char cvsroot[] = "$Header$";
#include "swig.h"
/* Declarations */
typedef struct {
int x, y;
} Foo;
...
/* Private Declarations (used only in this file) */
static int avariable;
...
/* Functions */
...
</pre>
</blockquote>
The CVS revision tag should be placed into a static string as shown
above. This adds the revision information to the SWIG executable and
makes it possible to extract version information from a raw binary
(sometimes useful in debugging).
<p>
As a general rule, files start to get unmanagable once they exceed
about 2000 lines. Files larger than this should be broken up into
multiple files. Similarly, you should avoid the temptation to create
many small files as this increases compilation time and makes the
directory structure too complicated.
<a name="6" href="#i6">
<h2>6. Bottom-Up Design </h2>
</a>
Within each source file, the preferred organization is to use what is
known as "bottom-up" design. Under this scheme, lower-level functions
appear first and the highest level function appears last. The easy
way to remember is that the "main" function of your module should
always appear last in the source file. For example:
<blockquote>
<pre>
/* Simple bottom-up program */
#include &lt;stdio.h&gt;
int foo(int x, int y) {
/* Implement foo */
...
}
int bar() {
...
foo(i,j);
...
}
...
int main(int argc, char **argv) {
...
bar();
...
}
</pre>
</blockquote>
This choice of design is somewhat arbitrary however it has a number of
benefits particular to C. In particular, a bottom-up design generally
eliminates the need to include forward references--resulting in
cleaner code and fewer compilation errors.
<a name="7" href="#i7">
<h2>7. Functions</h2>
</a>
All functions should have a function header that gives the function name
and a short description like this:
<blockquote>
<pre>
/* -------------------------------------------------------------------------
* Swig_add_directory()
*
* Adds a directory to the SWIG search path.
* ------------------------------------------------------------------------- */
void
Swig_add_directory(DOH *dirname) {
...
}
</pre>
</blockquote>
In the function declaration, the return type and any specifiers
(extern or static) should appear on a separate line followed by the
function name and arguments as shown above. The left curly brace
should appear on the same line as the function name.
<p>
Function declarations should <b>NOT</b> use the pre-ANSI function
declaration syntax. The ANSI standard has been around long enough for
this to be a non-issue.
<a name="8" href="#i8">
<h2>8. Naming Conventions</h2>
</a>
The following conventions are used to name various objects throughout SWIG.
<h4>Functions</h4>
Functions should consist of the module name and the function name separated by an underscore like this:
<blockquote>
<pre>
Preprocessor_define()
Swig_add_directory()
</pre>
</blockquote>
In general, the module name should match the name of the module
subdirectory and the function name should be in all lowercase with
words separated by underscores.
<h4>Structures and Types</h4>
If your module defines new structures, the structure name should include the name of the
module and the name of the structure appended together like this:
<blockquote>
<pre>
typedef struct SwigScanner {
...
} SwigScanner;
typedef struct LParseType {
...
} LParseType;
</pre>
</blockquote>
In this case, both the name of the module and the type should be capitalized. Also, whenever
possible, you should use the "typedef struct Name { ... } Name" form when defining new
data structures.
<h4>Global Variables</h4>
Global variables should be avoided if at all possible. However, if you must use a global
variable, please prepend the module name and use the same naming scheme as for functions.
<h4>Constants</h4>
Constants should be created using #define and should be in all caps like this:
<blockquote>
<pre>
#define SWIG_TOKEN_LPAREN 1
</pre>
</blockquote>
Separate words in a constant should be separated by underscores as with functions.
<h4>Structure members</h4>
Structure members should be in all lower-case and follow the same word-separation convention
as for function names. However, the module name does not have to be included.
For example:
<blockquote>
<pre>
typedef struct SwigScanner {
DOH *text; /* Current token value */
DOH *scanobjs; /* Objects being scanned */
DOH *str; /* Current object being scanned */
char *idstart; /* Optional identifier start characters */
int next_token; /* Next token to be returned */
int start_line; /* Starting line of certain declarations */
int yylen; /* Length of text pushed into text */
DOH *file; /* Current file name */
} SwigScanner;
</pre>
</blockquote>
<h4>Static Functions and Variables </h4>
Static declarations are free to use any naming convention that is appropriate. However, most
existing parts of SWIG use lower-case names and follow the same convention as described for functions.
<a name="9" href="#i9">
<h2>9. Visibility</h2>
</a>
Modules should keep the following rules in mind when exposing their internals:
<ul>
<li>Only publicly accessible functions should be included in the module header file.
<li>All non-static declarations must be prepended with some form of the module name
to avoid potential linker namespace conflicts with other modules.
<li>Modules should not expose global variables or use global variables in their
public interface.
<li>Similarly, modules should discourage the direct manipulation of data contained
within data structures in favor of using function calls instead. For example,
instead of providing a user with a structure like this:
<blockquote>
<pre>
typedef struct Foo {
int line;
} Foo;
</pre>
</blockquote>
It is better to hide the implementation of Foo and provide an
function-call interface like this:
<blockquote>
<pre>
typedef struct Foo Foo;
extern int Foo_getline(Foo *f);
extern void Foo_setline(Foo *f, int line);
</pre>
</blockquote>
Although this results in worse performance, there are many practical
reasons for doing this. The most important reason is that it allows
you to change the internal representation of Foo without breaking all
of the other modules or having to recompile the entire universe after
making your changes.
</ul>
<a name="10" href="#i10">
<h2>10. Miscellaneous Coding Guidelines</h2>
</a>
<ul>
<li> Do not use the ternary ?: operator. It is unnecessarily error prone,
hard for people to read, and hard to maintain code that uses it.
[I don't agree w/ this guideline. ?: operator can be abused
just like everything else, but it can also be used cleanly. In some styles of
programming, it is the best tool for the job. --ttn]
</ul>
<a name="11" href="#i11">
<h2>11. CVS Tagging Conventions</h2>
</a>
Use <tt>cvs tag</tt> to declare some set of file revisions as related in some
symbolic way. This eases reference, retrieval and manipulation of these files
later. At the moment (2001/01/16 14:02:53), the conventions are very simple;
let's hope they stay that way!
<p>
There are two types of tags, internal (aka personal) and external.
Internal tags are used by SWIG developers primarily, whereas external
tags are used when communicating with people w/ anonymous cvs access.
<ul>
<li> Internal tags should start with the developer name and a hyphen.
<li> External tags should start with "v-".
</ul>
That's all there is to it. Some example tags:
<ul>
<li> ttn-pre-xml-patch
<li> ttn-post-xml-patch
<li> ttn-going-on-vacation-so-dutifully-tagging-now
<li> v-1-3-a37-fixes-bug-2432
<li> v-1-3-a37-fixes-bug-2433
<li> v-1-3-a37-fixes-bug-2432-again
<li> v-1-3-a37-release
</ul>
<hr>
Copyright (C) 1999-2001
<a href="mailto:swig-dev@cs.uchicago.edu">SWIG Development Team</a>
</body>
</html>

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<html>
<head>
<title>SWIG Documentation</title>
</head>
<body>
This directory contains SWIG documentation:
<ul>
<li><a href="engineering.html">Engineering Manual</a>
<li><a href="internals.html">Internals Manual</a>
<li><a href="migrate.txt">SWIG1.3 Migration Guide</a>
</ul>
<hr>
Copyright (C) 1999-2001
<a href="mailto:swig-dev@cs.uchicago.edu">SWIG Development Team</a>
</body>
</html>

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<html>
<head>
<title>SWIG Internals</title>
</head>
<body>
<center>
<h1>SWIG Internals Manual</h1>
<b>Thien-Thi Nguyen <br>
ttn@glug.org <br>
<p>
David M. Beazley <br>
beazley@cs.uchicago.edu </br>
</b>
</center>
<p>
<b>$Header$</b>
<p>
(Note : This is a work in progress.)
<h2>Table of Contents</h2>
<ul>
<li><a name="i1" href="#1">1. Introduction</a>
<ul>
<li><a name="i1.1" href="#1.1">1.1 Directory Guide</a>
<li><a name="i1.2" href="#1.2">1.2 Overall Program Flow</a>
</ul>
<li><a name="i2" href="#2">2. DOH</a>
<ul>
<li><a name="i2.1" href="#2.1">2.1 Motivation and Background</a>
<li><a name="i2.2" href="#2.2">2.2 Basic Types</a>
<li><a name="i2.3" href="#2.3">2.3 Creating, Copying and Destroying Objects</a>
<li><a name="i2.4" href="#2.4">2.4 A Word About Mutability and Copying</a>
<li><a name="i2.5" href="#2.5">2.5 Strings</a>
<li><a name="i2.6" href="#2.6">2.6 Lists</a>
<li><a name="i2.7" href="#2.7">2.7 Hash Tables</a>
<li><a name="i2.8" href="#2.8">2.8 Files</a>
<li><a name="i2.9" href="#2.9">2.9 Void Objects</a>
<li><a name="i2.10" href="#2.10">2.10 Utility Functions</a>
</ul>
<li><a name="i3" href="#3">3. Types and Typemaps</a>
<li><a name="i4" href="#4">4. Parsing</a>
<li><a name="i5" href="#5">5. Difference Between SWIG 1.1 and SWIG 1.3</a>
<li><a name="i6" href="#6">6. Plans for SWIG 2.0</a>
<li><a name="i7" href="#7">7. C/C++ Wrapper Support Functions</a>
<li><a name="i8" href="#8">8. Reserved</a>
<li><a name="i9" href="#9">9. Reserved</a>
<li><a name="i10" href="#10">10. Guile Support</a>
<li><a name="i11" href="#11">11. Python Support</a>
<li><a name="i12" href="#12">12. Perl Support</a>
<li><a name="i13" href="#13">13. Java Support</a>
</ul>
<a name="1" href="#i1">
<h2>1. Introduction</h2>
</a>
This document details SWIG internals: architecture and sometimes
implementation. The first few sections concentrate on data structures,
interfaces, conventions and code shared by all language targets.
Subsequent sections focus on a particular language.
<p>
The audience is assumed to be SWIG developers (who should also read the
<a href="engineering.html">SWIG Engineering Manual</a> before starting
to code).
<a name="1.1" href="#i1.1">
<h3>1.1 Directory Guide</h3>
</a>
<table border=1>
<tr><td><a href="index.html">Doc</a></td>
<td>HTML documentation. If you find a documentation bug, please
<a href="mailto:bug-swig-doc@glug.org">let us know</a>.</td>
</tr>
<tr><td>Examples</td>
<td>This subdir tree contains examples of using SWIG w/ different
scripting languages, including makefiles. Typically, there are the
"simple" and "matrix" examples, w/ some languages offering additional
examples. The GIFPlot example has its own set of per-language
subdirectories. See the README more index.html file in each directory
for more info. [FIXME: Ref SWIG user manual.]</td>
</tr>
<tr><td>Lib</td>
<td>These are the <tt>.i</tt> (interface) files that form the SWIG
installed library. Language-specific files are in subdirectories (for
example, guile/typemaps.i). Each language also has a <tt>.swg</tt> file
implementing runtime type support for that language. The SWIG library
is not versioned.</td>
</tr>
<tr><td>Misc</td>
<td>Currently this subdir only contains file <tt>fileheader</tt>. See
the <a href="engineering.html">Engineering Manual</a> for more
info.</td>
</tr>
<tr><td>Runtime</td>
<td>This subdir contains scripts and a makefile for creating runtime
shared-object libraries used by various languages. Runtime/make.sh
says: "The runtime libraries are only needed if you are building
multiple extension modules that need to share information."</td>
</tr>
<tr><td>Source</td>
<td>SWIG source code is in this subdir tree. Directories marked w/ "(*)"
are used in building the <tt>swig</tt> executable.
<table border=1>
<tr><td>DOH (*)</td>
<td>C library providing memory allocation, file access and generic
containers. Result: libdoh.a</td>
</tr>
<tr><td>Experiment</td>
<td>[TODO]</td>
</tr>
<tr><td>Include (*)</td>
<td>Configuration .h files</td>
</tr>
<tr><td>LParse</td>
<td>Parser (lex / yacc) files and support [why not (*)?!]</td>
</tr>
<tr><td>Modules</td>
<td>[TODO]</td>
</tr>
<tr><td>Modules1.1 (*)</td>
<td>Language-specific callbacks that does actual code generation (each
language has a .cxx and a .h file). Result: libmodules11.a</td>
</tr>
<tr><td>Preprocessor (*)</td>
<td>SWIG-specialized C/C++ preprocessor. Result: libcpp.a</td>
</tr>
<tr><td>SWIG1.1 (*)</td>
<td>Parts of SWIG that are not language-specific, including option
processing and the type-mapping system. Result: libswig11.a.
Note: This directory is currently being phased out. </td>
</tr>
<tr><td>SWIG1.3</td>
<td>[TODO] [funny, nothing here is presently used for swig-1.3].
This directory might turn into a compatibility interface between
SWIG1.3 and the SWIG1.1 modules.</td>
</tr>
<tr><td>Swig (*)</td>
<td>This directory contains the new ANSI C core of the system
and contains generic functions related to types, file handling,
scanning, and so forth.</td>
</tr>
</table></td>
</tr>
<tr><td>Tools</td>
<td>Libtool support and the mkdist.py script.</td>
</tr>
<tr><td>Win</td>
<td>This improperly-named (spit spit) subdir only has README.txt.</td>
</tr>
</table>
<a name="1.2" href="#1.2">
<h3>1.2 Overall Program Flow</h3>
</a>
Here is the general control flow and where under subdir <tt>Source</tt>
to look for code:
<ul>
<li> <tt>Modules1.1/swigmain.cxx:main()</tt> is the program entry
point. It parses the language-specifying command-line option (for
example, <tt>-java</tt>), creating a new language-specific wrapping
object (each language is a C++ class derived from base class
<tt>Language</tt>). This object and the command-line is passed to
<tt>SWIG_main()</tt>, whose return value is the program exit value.
<li> <tt>SWIG1.1/main.cxx:SWIG_main()</tt> is the "real" main. It
initializes the preprocessor and typemap machinery, defines some
preprocessor symbols, locates the SWIG library, processes common
command-line options, and then calls the language-specific command-line
parser. From here there are three paths: "help", "checkout" and
everything else.
<ul>
<li> In "help" mode, clean up open files and exit.
<li> In "checkout" mode, copy specified files from the SWIG library
to the current directory. Errors cause error messages but no
non-lcoal exits.
<li> Otherwise, do wrapping: determine output file name(s), define
some preprocessor symbols and run the preprocessor, initialize
the interface-definition parser, set up the typemap for handling
new return strings, and finally do the language-specific parse
(by calling the language object's <tt>parse()</tt> method), which
creates output files by side-effect.
</ul>
Afterwards, remove temporary files, and clean up. If the command-line
included <tt>-freeze</tt>, go into an infinite loop; otherwise return the
error count.
<li> The language-specific <tt>parse()</tt> (and all other
language-specific code) lives in <tt>Modules1.1/foo.{h,cxx}</tt> for
language Foo. Typically, <tt>FOO::parse()</tt> calls
<tt>FOO::headers()</tt> and then the global function <tt>yyparse()</tt>,
which uses the callbacks registered by <tt>SWIG_main()</tt> above.
</ul>
<a name="2" href="#i2">
<h2>2. DOH</h2>
</a>
DOH is a collection of low-level objects such as strings, lists, and
hash tables upon which the rest of SWIG is built. The name 'DOH'
unofficially stands for "Dave's Object Hack", but it's also a good
expletive to use when things don't work (as in "SWIG core
dumped---DOH!").
<a name="2.1" href="#2.1">
<h3>2.1 Motivation and Background</h3>
</a>
The development of DOH is influenced heavily by the problems
encountered during earlier attempts to create a C++ based version of
SWIG2.0. In each of these attempts (over a 3 year period), the
resulting system always ended up growing into a collossal nightmare of
large inheritance hierarchies and dozens of specialized classes for
different types of objects (functions, variables, constants, etc.).
The end result was that the system was tremendously complicated,
difficult to understand, difficult to maintain, and fairly inflexible
in the grand scheme of things.
<p>
DOH takes a different approach to tackling the complexity problem.
First, rather than going overboard with dozens of types and class
definitions, DOH only defines a handful of simple yet very useful
objects that are easy to remember. Second, DOH uses dynamic
typing---one of the features that make scripting languages so useful
and which make it possible to accomplish things with much less code.
Finally, DOH utilizes a few coding tricks that allow it to perform
a limited form of function overloading for certain C datatypes (more
on that a little later).
<p>
The key point to using DOH is that instead of thinking about code in
terms of highly specialized C data structures, just about everything
ends up being represented in terms of a just a few datatypes. For
example, structures are replaced by DOH hash tables whereas arrays are
replaced by DOH lists. At first, this is probably a little strange to
most C/C++ programmers, but in the long run in makes the system
extremely flexible and highly extensible. Also, in terms of coding,
many of the newly DOH-based subsystems are less than half the size (in
lines of code) of the earlier C++ implementation.
<a name="2.2" href="#i2.2">
<h3>2.2 Basic Types</h3>
</a>
The following built-in types are currently provided by DOH:
<ul>
<li><b>String</b>. A string of characters with automatic memory
management and high-level operations such as string replacement. In addition,
strings support file I/O operations that make it possible to use them just
about anyplace a file can be used.
<p>
<li><b>List</b>. A list of arbitrary DOH objects (of possibly mixed types).
<p>
<li><b>Hash</b>. A hash table that maps a set of string keys to a set of arbitrary
DOH objects. The DOH version of an associative array for all of you Perl fans.
<p>
<li><b>File</b>. A DOH wrapper around the C FILE * structure. This is provided
since other objects sometimes want to behave like files (strings for instance).
<p>
<li><b>Void</b>. A DOH wrapper around an arbitrary C pointer. This can be used
if you want to place arbitrary C data structures in DOH lists and hash tables.
</ul>
Due to dynamic typing, all of the objects in DOH are represented by pointers
of type <tt>DOH *</tt>. Furthermore, all objects are completely
opaque--that means that the only way to access the internals of an
object is through a well-defined public API. For convenience, the following
symbolic names are sometimes used to improve readability:
<ul>
<Li><tt>DOHString *</tt>. A String object.
<li><tt>DOHList *</tt>. A list object.
<li><tt>DOHHash *</tt>. A hash object.
<li><tt>DOHFile *</tt>. A file object.
<li><tt>DOHVoid *</tt>. A void object.
<li><tt>DOHString_or_char *</tt>. A DOH String object or a raw C "char *".
</ul>
It should be stressed that all of these names are merely symbolic aliases to the
type <tt>DOH *</tt> and that no compile-time type checking is performed (of course,
a runtime error may occur if you screw up).
<a name="2.3" href="#i2.3">
<h3>2.3 Creating, Copying, and Destroying Objects </h2>
</a>
The following functions can be used to create new DOH objects
<ul>
<Li><tt>NewString(DOHString_or_char *value)</tt><br>
Create a new string object with contents initially
set to value. value can be either a C string or a DOH string object.
<p>
<li><tt>NewStringf(char *fmt, ...)</tt><br>
Create a new string object with contents initially set to
a formatted string. Think of this as being sprintf() combined with an object constructor.
<p>
<li><tt>NewList()</tt><br>
Create a new list object that is initially empty.
<p>
<Li><tt>NewHash()</tt><br>
Create a new hash object that is initially empty.
<p>
<li><tt>NewFile(DOHString_or_char *filename, char *mode)</tt><br>
Open a file and return a file object. This is a
wrapper around the C <tt>fopen()</tt> library call.
<p>
<li><tt>NewFileFromFile(FILE *f)</tt><br>
Create a new file object given an already opened <tt>FILE *</tt> object.
<p>
<li><tt>NewVoid(void *obj, void (*del)(void *))</tt><br>
Create a new DOH object that is a wrapper around an
arbitrary C pointer. <tt>del</tt> is an optional destructor function that will be called when the object
is destroyed.
</ul>
Any object can be copied using the <tt>Copy()</tt> function. For example:
<blockquote>
<pre>
DOH *a, *b, *c, *d;
a = NewString("Hello World");
b = NewList();
c = Copy(a); /* Copy the string a */
d = Copy(b); /* Copy the list b */
</pre>
</blockquote>
Copies of lists and hash tables are shallow. That is, their contents are only copied by reference.
<p>
Objects can be deleted using the <tt>Delete()</tt> function. For example:
<blockquote>
<pre>
DOH *a = NewString("Hello World");
...
Delete(a); /* Destroy a */
</pre>
</blockquote>
All objects are referenced counted and given a reference count of 1 when initially created. The
<tt>Delete()</tt> function only destroys an object when the reference count reaches zero. When
an object is placed in a list or hash table, it's reference count is automatically increased. For example:
<blockquote>
<pre>
DOH *a, *b;
a = NewString("Hello World");
b = NewList();
Append(b,a); /* Increases refcnt of a to 2 */
Delete(a); /* Decreases refcnt of a to 1 */
Delete(b); /* Destroys b, and destroys a */
</pre>
</blockquote>
Should it ever be necessary to manually increase the reference count of an object, the DohIncref() function
can be used:
<blockquote>
<pre>
DOH *a = NewString("Hello");
DohIncref(a);
</pre>
</blockquote>
<a name="2.4" href="#i2.4">
<h3>2.4 A Word About Mutability and Copying</h3>
</a>
All DOH objects are mutable regardless of their current reference
count. For example, if you create a string and then create a 1000
references to it (in lists and hash tables), changes to the string
will be reflected in all of the references. Therefore, if you need to
make any kind of local change, you should first make a copy using the
Copy() function. Caveat: when copying lists and hash tables, elements
are copied by reference.
<a name="2.5" href="#i2.5">
<h3>2.5 Strings</h3>
</a>
The DOH String type is perhaps the most flexible object. First, it supports a variety of string-oriented
operations. Second, it supports many of the same operations as lists. Finally, strings provide file I/O
operations that allow them to be used interchangably with DOH file objects.
[ TODO ]
<a name="2.6" href="#i2.6">
<h3>2.6 Lists</h3>
</a>
[ TODO ]
<a name="2.7" href="#i2.7">
<h3>2.7 Hash tables </h3>
</a>
[ TODO ]
<a name="2.8" href="#i2.8">
<h3>2.8 Files </h3>
</a>
[ TODO ]
<a name="2.9" href="#i2.9">
<h3>2.9 Void objects </h3>
</a>
[ TODO ]
<a name="2.10" href="#i2.10">
<h3>2.10 Utility functions </h3>
</a>
[ TODO ]
<a name="3" href="#i3">
<h2>3. Types and Typemaps</h2>
</a>
Revised: Dave Beazley (8/14/00)
<p>
The representation and manipulation of types is currently in the
process of being reorganized and (hopefully) simplified. The
following list describes the current set of functions that are used to
manipulate datatypes. These functions are different than in
SWIG1.1 and may change names in the final SWIG1.3 release.
<ul>
<li><tt>SwigType_str(SwigType *t, char *name)</tt>.<br>
This function produces the exact string
representation of the datatype <tt>t</tt>. <tt>name</tt> is an optional parameter that
specifies a declaration name. This is used when dealing with more complicated datatypes
such as arrays and pointers to functions where the output might look something like
"<tt>int (*name)(int, double)</tt>".
<p>
<li><tt>SwigType_lstr(SwigType *t, char *name)</tt>.<br>
This function produces a string
representation of a datatype that can be safely be assigned a value (i.e., can be used as the
"lvalue" of an expression). To do this, qualifiers such as "const", arrays, and references
are stripped away or converted into pointers. For example:
<blockquote>
<pre>
Original Datatype lstr()
------------------ --------
const char *a char *a
double a[20] double *a
double a[20][30] double *a
double &a double *a
</pre>
</blockquote>
The intent of the lstr() function is to produce local variables inside wrapper functions--all
of which must be reassignable types since they are the targets of conversions from a scripting
representation.
<p>
<li><tt>SwigType_rcaststr(SwigType *t, char *name)</tt>.
<br> This function produces a string
that casts a type produced by the <tt>lstr()</tt> function to the type produced by the
<tt>str()</tt> function. You might view it as the inverse of lstr(). This function only produces
output when it needs to (when str() and lstr() produce different results). Furthermore, an optional
name can be supplied when the cast is to be applied to a specific name. Examples:
<blockquote>
<pre>
Original Datatype rcaststr()
------------------ ---------
char *a
const char *a (const char *) name
double a[20] (double *) name
double a[20][30] (double (*)[30]) name
double &a (double &) *name
</pre>
</blockquote>
<p>
<li><tt>SwigType_lcaststr(SwigType *t, char *name)</tt>.
<br> This function produces a string
that casts a type produced by the <tt>str()</tt> function to the type produced by the
<tt>lstr()</tt> function. This function only produces
output when it needs to (when str() and lstr() produce different results). Furthermore, an optional
name can be supplied when the cast is to be applied to a specific name.
<blockquote>
<pre>
Original Datatype lcaststr()
------------------ ---------
char *a
const char *a (char *) name
double a[20] (double *) name
double a[20][30] (double *) name
double &a (double *) &name
</pre>
</blockquote>
<p>
<li><tt>SwigType_manglestr(SwigType *t)</tt>. <br>
Produces a type-string that is used to identify this datatype in the target scripting language.
Usually this string looks something like "<tt>_p_p_double</tt>" although the target language
may redefine the output for its own purposes. Normally this function strips all qualifiers,
references, and arrays---producing a mangled version of the type produced by the <tt>lstr()</tt> function.
</ul>
The following example illustrates the intended use of the above functions when creating wrapper
functions using shorthand pseudocode. Suppose you had a function like this:
<blockquote>
<pre>
int foo(int a, double b[20][30], const char *c, double &amp;d);
</pre>
</blockquote>
Here's how a wrapper function would be generated using the type generation functions above:
<blockquote>
<pre>
wrapper_foo() {
lstr("int","result")
lstr("int","arg0")
lstr("double [20][30]", "arg1")
lstr("const char *", "arg2")
lstr("double &amp;", "arg3")
...
get arguments
...
result = (lcaststr("int")) foo(rcaststr("int","arg0"),
rcaststr("double [20][30]","arg1"),
rcaststr("const char *", "arg2"),
rcaststr("double &amp;", "arg3"))
...
}
</pre>
</blockquote>
Here's how it would look with the corresponding output filled in:
<blockquote>
<pre>
wrapper_foo() {
int result;
int arg0;
double *arg1;
char *arg2;
double *arg3;
...
get arguments
...
result = (int) foo(arg0,
(double (*)[30]) arg1,
(const char *) arg2,
(double &amp;) *arg3);
...
}
</pre>
</blockquote>
<b>Notes:</b>
<ul>
<li>For convenience, the string generation functions return a
"<tt>char *</tt>" that points to statically allocated memory living
inside the type library. Therefore, it is never necessary (and it's
an error) to free the pointer returned by the functions. Also, if you
need to save the result, you should make a copy of it. However, with
that said, it is probably worth nothing that these functions do cache
the last 8 results. Therefore, it's fairly safe to make a handful of
repeated calls without making any copies.
</ul>
[TODO]
<a name="4" href="#i4">
<h2>4. Parsing</h2>
</a>
[TODO]
<a name="5" href="#i5">
<h2>5. Difference Between SWIG 1.1 and SWIG 1.3</h2>
</a>
[TODO]
<a name="6" href="#i6">
<h2>6. Plans for SWIG 2.0</h2>
</a>
[TODO]
<a name="7" href="#i7">
<h2>7. The C/C++ Wrapping Layer</h2>
</a>
Added: Dave Beazley (July 22, 2000)
<p>
When SWIG generates wrappers, it tries to provide a mostly seamless integration
with the original code. However, there are a number of problematic features
of C/C++ programs that complicate this interface.
<ul>
<li><b>Passing and returning structures by value.</b> When used, SWIG converts
all pass-by-value functions into wrappers that pass by reference. For example:
<blockquote>
<pre>
double dot_product(Vector a, Vector b);
</pre>
</blockquote>
gets turned into a wrapper like this:
<blockquote>
<pre>
double wrap_dot_product(Vector *a, Vector *b) {
return dot_product(*a,*b);
}
</pre>
</blockquote>
Functions that return by value require a memory allocation to store the result. For example:
<blockquote>
<pre>
Vector cross_product(Vector *a, Vector *b);
</pre>
</blockquote>
become
<blockquote>
<pre>
Vector *wrap_cross_product(Vector *a, Vector *b) {
Vector *result = (Vector *) malloc(sizeof(Vector));
*result = cross_product(a,b);
return result;
}
</pre>
</blockquote>
Note: If C++ is being wrapped, the default copy constructor is used
instead of malloc() to create a copy of the return result.
<p>
<li><b>C++ references</b>. C++ references are handled exactly the same as
pass/return by value except that a memory allocation is not made for functions
that return a reference.
<p>
<li><b>Qualifiers such as "const" and "volatile".</b> SWIG strips all
qualifiers from the interface presented to the target language.
Besides, what in the heck is "const" in Perl anyways?
<p>
<li><b>Instance Methods</b>. Method invocations are handled as a function call in which
a pointer to the object (the "this" pointer) appears as the first argument. For example, in
the following class:
<blockquote>
<pre>
class Foo {
public:
double bar(double);
};
</pre>
</blockquote>
The "bar" method is wrapped by a function like this:
<blockquote>
<pre>
double Foo_bar(Foo *self, double arg0) {
return self->bar(arg0);
}
</pre>
</blockquote>
<p>
<li><b>Structure/class data members</b>. Data members are handled by creating a pair
of wrapper functions that set and get the value respectively. For example:
<blockquote>
<pre>
struct Foo {
int x;
};
</pre>
</blockquote>
gets wrapped as follows:
<blockquote>
<pre>
int Foo_x_get(Foo *self) {
return self->x;
}
int Foo_x_set(Foo *self, int value) {
return (self->x = value);
}
</pre>
</blockquote>
<p>
<li><b>Constructors</b>. Constructors for C/C++ data structures are wrapped by
a function like this:
<blockquote>
<pre>
Foo *new_Foo() {
return new Foo;
}
</pre>
</blockquote>
Note: For C, new objects are created using the calloc() function.
<p>
<li><b>Destructors</b>. Destructors for C/C++ data structures are wrapper like this:
<blockquote>
<pre>
void delete_Foo(Foo *self) {
delete self;
}
</pre>
</blockquote>
Note: For C, objects are destroyed using free().
</ul>
The creation of wrappers and various type transformations are handled by a collection of functions
found in the file <tt>Source/Swig/cwrap.c</tt>.
<ul>
<li>
<tt>char *Swig_clocal(DataType *t, char *name, char *value)</tt><br>
This function creates a string containing the declaration of a local variable with
type <tt>t</tt>, name <tt>name</tt>, and default value <tt>value</tt>. This local
variable is stripped of all qualifiers and will be a pointer if the type is a reference
or user defined type.
<p>
<li>
<tt>DataType *Swig_clocal_type(DataType *t)</tt><br>
Returns a type object corresponding to the type string produced by the Swig_clocal() function.
<p>
<li><tt>char *Swig_clocal_deref(DataType *t, char *name)</tt><br>
This function is the inverse of the <tt>clocal()</tt> function. Given a type and a name,
it produces a string containing the code needed to cast/convert the type produced by
<tt>Swig_clocal()</tt> back into it's original type.
<p>
<li><tt>char *Swig_clocal_assign(DataType *t, char *name)</tt><br>
Given a type and name, this produces a string containing the code (and an optional cast)
needed to make an assignment from the real datatype to the local datatype produced
by <tt>Swig_clocal()</tt>. Kind of the opposite of deref().
<p>
<li><tt>int Swig_cargs(Wrapper *w, ParmList *l)</tt><br>
Given a wrapper function object and a list of parameters, this function declares a set
of local variables for holding all of the parameter values (using Swig_clocal()). Returns
the number of parameters. In addition, this function sets the local name of each parameter
which can be retrieved using the <tt>Parm_Getlname()</tt> function.
<p>
<li><tt>void Swig_cresult(Wrapper *w, DataType *t, char *resultname, char *decl)</tt><br>
Generates the code needed to set the result of a wrapper function and performs all of
the needed memory allocations for ANSI C (if necessary). <tt>t</tt> is the type of the
result, <tt>resultname</tt> is the name of the result variable, and <tt>decl</tt> is
a string that contains the C code which produces the result.
<p>
<li><tt>void Swig_cppresult(Wrapper *w, DataType *t, char *resultname, char *decl)</tt><br>
Generates the code needed to set the result of a wrapper function and performs all of
the needed memory allocations for C++ (if necessary). <tt>t</tt> is the type of the
result, <tt>resultname</tt> is the name of the result variable, and <tt>decl</tt> is
a string that contains the C code which produces the result.
<p>
<li><tt>Wrapper *Swig_cfunction_wrapper(char *fname, DataType *rtype, ParmList *parms, char *code)</tt><br>
Create a wrapper around a normal function declaration. <tt>fname</tt> is the name of the wrapper,
<tt>rtype</tt> is the return type, <tt>parms</tt> are the function parameters, and <tt>code</tt> is a
string containing the code in the function body.
<p>
<li><tt>Wrapper *Swig_cmethod_wrapper(char *classname, char *methodname, DataType *rtype, DataType *parms, char *code)</tt><br>
<p>
<li><tt>char *Swig_cfunction_call(char *name, ParmList *parms)</tt>
This function produces a string containing the code needed to call a C function.
The string that is produced contains all of the transformations needed to convert
pass-by-value into pass-by-reference as well as handle C++ references. Produces
a string like "name(arg0, arg1, ..., argn)".
</ul>
Here is a short example showing how these functions could be used. Suppose you had a
C function like this:
<blockquote>
<pre>
double dot_product(Vector a, Vector b);
</pre>
</blockquote>
Here's how you might write a really simple wrapper function
<blockquote>
<pre>
ParmList *l = ... parameter list of the function ...
DataType *t = ... return type of the function ...
char *name = ... name of the function ...
Wrapper *w = NewWrapper();
Printf(w->def,"void wrap_%s() {\n", name);
/* Declare all of the local variables */
Swig_cargs(w, l);
/* Convert all of the arguments */
...
/* Make the function call and declare the result variable */
Swig_cresult(w,t,"result",Swig_cfunction(name,l));
/* Convert the result into whatever */
...
Printf(w->code,"}\n");
Wrapper_print(w,out);
</pre>
</blockquote>
The output of this would appear as follows:
<blockquote>
<pre>
void wrap_dot_product() {
Vector *arg0;
Vector *arg1;
double result;
...
result = dot_product(*arg0, *arg1);
...
}
</pre>
</blockquote>
Notice that the <tt>Swig_cargs()</tt>, <tt>Swig_cresult()</tt>, and <tt>Swig_cfunction()</tt> functions
have taken care of the type conversions for the <tt>Vector</tt> type automatically.
<p>
<b>Notes:</b>
<ul>
<Li>The intent of these functions is to provide <em>consistent</em> handling of function parameters
and return values so that language module writers don't have to worry about it too much.
<p>
<li>These functions may be superceded by features in the new typemap system which provide hooks
for specifying local variable declarations and argument conversions.
</ul>
<a name="8" href="#i8">
<h2>8. Reserved</h2>
</a>
<a name="9" href="#i9">
<h2>9. Reserved</h2>
</a>
<a name="10" href="#i10">
<h2>10. Guile Support</h2>
</a>
The information that used to live here has moved to the user
documentation, file <code>Guile.html</code>.
<a name="11" href="#i11">
<h2>11. Python Support</h2>
</a>
[TODO]
<a name="12" href="#i12">
<h2>12. Perl Support</h2>
</a>
[TODO]
<a name="13" href="#i13">
<h2>13. Java Support</h2>
</a>
[TODO]
<hr>
Copyright (C) 1999-2001
<a href="mailto:swig-dev@cs.uchicago.edu">SWIG Development Team</a>
</body>
</html>

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SWIG1.3 Migration Guide
(The not entirely complete guide to updating language modules to work with SWIG1.3).
Dave Beazley
August 15, 2000
1. Introduction
---------------
Virtually all of SWIG's internal data structures have now been
rewritten. Take everything you thought you knew about SWIG1.1 and
throw it out.
2. DataTypes
------------
The old 'DataType' data structure is gone. Therefore, direct
manipulation of 'is_pointer', 'implicit_ptr', and 'arraystr'
attributes no longer applies. Sorry.
Datatypes are now represented by the type 'SwigType' which has no
public attributes. Actually, if you look at it closely, 'SwigType' is
really just an alias for 'void' and if you look at it even closer than
that you will realize that it's nothing more than a string!
The string encoding of types is described in more detail in the file
Source/Swig/stype.c and is not so important here. What is important is
the functions used to produce various types of output:
SwigType_str(type,name = 0);
This produces an exact C representation of the datatype with all
qualifiers, arrays, references, and so forth. name is an optional
name that is given if you wanted to associate the type with a
parameter name or something.
SwigType_lstr(type,name = 0);
This function takes a type and produces a C string containing
a type suitable for assignment (appearing as an lvalue in an
expression). To do this, certain things such as 'const',
arrays, and references are stripped away or converted into
pointers.
SwigType_ltype(type);
Returns a SwigType object corresponding to the type created
by SwigType_lstr().
SwigType_lcaststr(type,name);
Produces a string casting a value 'name' from the real datatype
to the assignable type created by SwigType_lstr().
SwigType_rcaststr(type,name)
Produces a string that casts a value 'name' from the type
created by SwigType_lstr() to the real datatype.
SwigType_manglestr(type)
Produces the 'mangled' version of a datatype.
Getting the 'type' code. Most language modules still operate by
looking at special integer type codes. This interface is a little
ragged and will probably go away at some point. However, for now the
following function can be used to get the type code:
int SwigType_type(type)
The codes are the same as the before, except that there are a few
special codes:
T_STRING - The 'char *' type and variations.
T_POINTER - Any pointer type (not char * though)
T_REFERENCE - Any C++ reference
T_ARRAY - Any array
T_FUNCTION - A function (this is usually an error).
Because of the special codes, it is no longer necessary to have code like this:
if ((t->is_pointer == 1) and (t->type == T_CHAR)) {
... get a string ...
}
Instead, just use the type code above like this:
switch(SwigType_type(type)) {
case T_STRING:
... get a string ...
break;
case T_POINTER:
... get a pointer ...
break;
}
There are about 2-dozen type manipulation functions that could also be useful.
See Source/Swig/swig.h and Source/Swig/stype.c.
3. Parameter Lists
------------------
The ParmList data structure is gone. In reality, parameter lists are nothing more than
a linked list of parameters. The proper way to iterate over this list and get
parameter values is as follows:
ParmList *l;
Parm *p;
for (p = l; p; p = Getnext(p)) {
SwigType *pt = Gettype(p); /* Get parameter type */
String *pn = Getname(p); /* Get parameter name */
String *value = Getvalue(p); /* Get parameter value */
...
do whatever
...
}
4. Typemaps
-----------
Typemaps more or less work. However, the interface has changed slightly. Instead of
typemap_lookup("in","python",type,pname,"$source","$target",wrapper);
the function is
Swig_typemap_lookup("in",type,pname,"$source","$target",wrapper);
There are a variety of other changes to typemaps (see CHANGES).
5. Use of new types
-------------------
When possible, language modules should try to use the built in String,
List, and Hash objects instead of C arrays or 'char *'. This will probably require a
detailed pass through the code with an eye towards cleanup.
6. Miscellaneous
----------------
Language modules no longer need to concern themselves with formatting the
wrapper code they produce (provided you are using the special Wrapper object).
The function Wrapper_print() passes everything through a pretty-printer that
automatically performs indentation and tries to clean things up. This especially
works well when there are lots of typemaps.