1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
|
<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>
<ul>
<li><a name="i10.1" href="#10.1">10.1 Meaning of "Module"</a>
<li><a name="i10.2" href="#10.2">10.2 Linkage</a>
<li><a name="i10.3" href="#10.3">10.3 Underscore Folding</a>
<li><a name="i10.4" href="#10.4">10.4 Typemaps</a>
<li><a name="i10.5" href="#10.5">10.5 Smobs</a>
<li><a name="i10.6" href="#10.6">10.6 Exception Handling</a>
<li><a name="i10.7" href="#10.7">10.7 Procedure documentation</a>
<li><a name="i10.8" href="#10.8">10.8 Procedures with setters</a>
</ul>
<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 &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 &", "arg3")
...
get arguments
...
result = (lcaststr("int")) foo(rcaststr("int","arg0"),
rcaststr("double [20][30]","arg1"),
rcaststr("const char *", "arg2"),
rcaststr("double &", "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 &) *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>
Revised: Matthias Köppe (August 30, 2000)
<p>
This section details guile-specific support in SWIG.
<a name="10.1" href="#i10.1">
<h3>10.1 Meaning of "Module"</h3>
</a>
<p>
There are three different concepts of "module" involved, defined
separately for SWIG, Guile, and Libtool. To avoid horrible confusion,
we explicitly prefix the context, e.g., "guile-module".
<a name="10.2" href="#i10.2">
<h3>10.2 Linkage</h3>
</a>
<p>
Guile support is complicated by a lack of user community cohesiveness,
which manifests in multiple shared-library usage conventions. A set of
policies implementing a usage convention is called a <b>linkage</b>.
The default linkage is the simplest; nothing special is done. In this
case <code>SWIG_init()</code> is provided and users must do something
like this:
<blockquote>
<pre>
(define my-so (dynamic-link "./example.so"))
(dynamic-call "SWIG_init" my-so)
</pre>
</blockquote>
At this time, the name <code>SWIG_init</code> is hardcoded; this
approach does not work with multiple swig-modules. NOTE: The "simple"
and "matrix" examples under Examples/guile include guilemain.i; the
resulting standalone interpreter does not require calls to
<code>dynamic-link</code> and <code>dynamic-call</code>, as shown here.
<p>
A second linkage creates "libtool dl module" wrappers, and currently is
broken. Whoever fixes this needs to track Guile's libtool dl module
convention, since that is not finalized.
<p>
The only other linkage supported at this time creates shared object
libraries suitable for use by hobbit's <code>(hobbit4d link)</code>
guile module. This is called the "hobbit" linkage, and requires also
using the "-package" command line option to set the part of the module
name before the last symbol. For example, both command lines:
[checkme:ttn]
<blockquote>
<pre>
swig -guile -package my/lib foo.i
swig -guile -package my/lib -module foo foo.i
</pre>
</blockquote>
would create module <code>(my lib foo)</code> (assuming in the first
case foo.i declares the module to be "foo"). The installed files are
my/lib/libfoo.so.X.Y.Z and friends. This scheme is still very
experimental; the (hobbit4d link) conventions are not well understood.
<p>
There are no other linkage types planned, but that could change... To
add a new type, add the name to the enum in guile.h and add the case to
<code>GUILE::emit_linkage()</code>.
<a name="10.3" href="#i10.3">
<h3>10.3 Underscore Folding</h3>
</a>
<p>
Underscores are converted to dashes in identifiers. Guile support may
grow an option to inhibit this folding in the future, but no one has
complained so far.
<a name="10.4" href="#i10.4">
<h3>10.4 Typemaps</h3>
</a>
<p>
The Guile module handles all non-pointer types via typemaps. This
information is read from <code>Lib/guile/typemaps.i</code>.
<a name="10.5" href="#i10.5">
<h3>10.5 Smobs</h3>
</a>
<p>
For pointer types, SWIG uses Guile smobs.
<p>
Currently, one wrapper module must be generated without
<code>-c</code> and compiled with <code>-DSWIG_GLOBAL</code>, all the
other wrapper modules must be generated with <code>-c</code>. Maybe
one should move all the global helper functions that come from
<code>guile.swg</code> into a library, which is built by <code>make
runtime</code>.
<p>
In earlier versions of SWIG, C pointers were represented as Scheme
strings containing a hexadecimal rendering of the pointer value and a
mangled type name. As Guile allows registering user types, so-called
"smobs" (small objects), a much cleaner representation has been
implemented now. The details will be discussed in the following.
<p>
A smob is a cons cell where the lower half of the CAR contains the
smob type tag, while the upper half of the CAR and the whole CDR are
available. <code>SWIG_Guile_Init()</code> registers a smob type named
"swig" with Guile; its type tag is stored in the variable
<code>swig_tag</code>. The upper half of the CAR store an index into
a table of all C pointer types seen so far, to which new types seen
are appended. The CDR stores the pointer value. SWIG smobs print
like this: <code>#<swig struct xyzzy * 0x1234affe></code> Two of
them are <code>equal?</code> if and only if they have the same type
and value.
<p>
To construct a Scheme object from a C pointer, the wrapper code calls
the function <code>SWIG_Guile_MakePtr()</code>, passing a pointer to a
struct representing the pointer type. The type index to store in the
upper half of the CAR is read from this struct.
<p>
To get the pointer represented by a smob, the wrapper code calls the
function <code>SWIG_Guile_GetPtr</code>, passing a pointer to a struct
representing the expected pointer type. If the
Scheme object passed was not a SWIG smob representing a compatible
pointer, a <code>wrong-type-arg</code> exception is raised.
<a name="10.6" href="#i10.6">
<h3>10.6 Exception Handling</h3>
</a>
<p>
SWIG code calls <code>scm_error</code> on exception, using the following
mapping:
<pre>
MAP(SWIG_MemoryError, "swig-memory-error");
MAP(SWIG_IOError, "swig-io-error");
MAP(SWIG_RuntimeError, "swig-runtime-error");
MAP(SWIG_IndexError, "swig-index-error");
MAP(SWIG_TypeError, "swig-type-error");
MAP(SWIG_DivisionByZero, "swig-division-by-zero");
MAP(SWIG_OverflowError, "swig-overflow-error");
MAP(SWIG_SyntaxError, "swig-syntax-error");
MAP(SWIG_ValueError, "swig-value-error");
MAP(SWIG_SystemError, "swig-system-error");
</pre>
<p>
The default when not specified here is to use "swig-error".
See Lib/exception.i for details.
<a name="10.7" href="#i10.7">
<h3>10.7 Procedure documentation</h3>
</a>
<p>If invoked with the command-line option <code>-procdoc
<var>file</var></code>, SWIG creates documentation strings for the
generated wrapper functions, describing the procedure signature and
return value, and writes them to <var>file</var>.
<p>You need to register the generated documentation file with Guile
like this:
<pre>
(use-modules (ice-9 documentation))
(set! documentation-files
(cons "<var>file</var>" documentation-files))
</pre>
This requires Guile 1.4 or later.
<p>Documentation strings can be configured using the Guile-specific
typemaps <code>indoc</code>, <code>outdoc</code>,
<code>argoutdoc</code>, <code>varindoc</code>, and
<code>varoutdoc</code>. See <code>Lib/guile/typemaps.i</code> for
details.
<a name="10.8" href="#i10.8">
<h3>10.8 Procedures with setters</h3>
</a>
<p>For global variables, SWIG creates a single wrapper procedure
<code>(<var>variable</var> :optional value)</code>, which is used for
both getting and setting the value. For struct members, SWIG creates
two wrapper procedures <code>(<var>struct</var>-<var>member</var>-get
pointer)</code> and <code>(<var>struct-member</var>-set pointer value)</code>.
<p>If invoked with the command-line option <code>-emit-setters</code>,
SWIG will additionally create procedures with setters. For global
variables, the procedure-with-setter <code><var>variable</var></code>
is created, so you can use <code>(<var>variable</var>)</code> to get
the value and <code>(set! (<var>variable</var>)
<var>value</var>)</code> to set it. For struct members, the
procedure-with-setter <code><var>struct</var>-<var>member</var></code>
is created, so you can use <code>(<var>struct</var>-<var>member</var>
<var>pointer</var>)</code> to get the value and <code>(set!
(<var>struct</var>-<var>member</var> <var>pointer</var>)
<var>value</var>)</code> to set it.
<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>
|
