summaryrefslogtreecommitdiff
path: root/README.EXT
blob: 4cfe80bd82252e94170ef03fc02f23c7a82d3139 (plain)
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
.\" README.EXT -  -*- Text -*- created at: Mon Aug  7 16:45:54 JST 1995

This document explains how to make extension libraries for Ruby.

1. Basic knowledge

In C, variables have types and data do not have types.  In contrast,
Ruby variables do not have a static type, and data themselves have
types, so data will need to be converted between the languages.

Data in Ruby are represented by C type `VALUE'.  Each VALUE data has
its data-type.

To retrieve C data from a VALUE, you need to:

 (1) Identify the VALUE's data type
 (2) Convert the VALUE into C data

Converting to the wrong data type may cause serious problems.


1.1 Data-types

The Ruby interpreter has the following data types:

	T_NIL		nil
	T_OBJECT	ordinary object
	T_CLASS		class
	T_MODULE	module
	T_FLOAT		floating point number
	T_STRING	string
	T_REGEXP	regular expression
	T_ARRAY		array
	T_FIXNUM	Fixnum(31bit integer)
	T_HASH		associative array
	T_STRUCT	(Ruby) structure
	T_BIGNUM	multi precision integer
	T_FILE		IO
	T_TRUE		true
	T_FALSE		false
	T_DATA		data
	T_SYMBOL        symbol

In addition, there are several other types used internally:

	T_ICLASS
	T_MATCH
	T_UNDEF
	T_VARMAP
	T_SCOPE
	T_NODE

Most of the types are represented by C structures.

1.2 Check Data Type of the VALUE

The macro TYPE() defined in ruby.h shows the data type of the VALUE.
TYPE() returns the constant number T_XXXX described above.  To handle
data types, your code will look something like this:

  switch (TYPE(obj)) {
    case T_FIXNUM:
      /* process Fixnum */
      break;
    case T_STRING:
      /* process String */
      break;
    case T_ARRAY:
      /* process Array */
      break;
    default:
      /* raise exception */
      rb_raise(rb_eTypeError, "not valid value");
      break;
  }

There is the data-type check function

  void Check_Type(VALUE value, int type)

which raises an exception if the VALUE does not have the type specified.

There are also faster check macros for fixnums and nil.

  FIXNUM_P(obj)
  NIL_P(obj)

1.3 Convert VALUE into C data

The data for type T_NIL, T_FALSE, T_TRUE are nil, true, false
respectively.  They are singletons for the data type.

The T_FIXNUM data is a 31bit length fixed integer (63bit length on
some machines), which can be convert to a C integer by using the
FIX2INT() macro.  There is also NUM2INT() which converts any Ruby
numbers into C integers.  The NUM2INT() macro includes a type check, so
an exception will be raised if the conversion failed.  NUM2DBL() can
be used to retrieve the double float value in same way.

To get char* from a VALUE, version 1.7 recommend to use new macros
StringValue() and StringValuePtr().  StringValue(var) replaces var's
value to the result of "var.to_str()".  StringValuePtr(var) does same
replacement and returns char* representation of var.  These macros
will skip the replacement if var is a String.  Notice that the macros
requires to take only lvalue as their argument, to change the value
of var in the replacement. 

In version 1.6 or earlier, STR2CSTR() was used to do same thing
but now it is obsoleted in version 1.7 because of STR2CSTR() has
a risk of dangling pointer problem in to_str() impliclit conversion.

Other data types have corresponding C structures, e.g. struct RArray
for T_ARRAY etc. The VALUE of the type which has corresponding structure
can be cast to retrieve the pointer to the struct.  The casting macro
will be of the form RXXXX for each data type; for instance, RARRAY(obj). 
See "ruby.h".

For example, `RSTRING(str)->len' is the way to get the size of the
Ruby String object.  The allocated region can be accessed by
`RSTRING(str)->ptr'.  For arrays, use `RARRAY(ary)->len' and
`RARRAY(ary)->ptr' respectively.

Notice: Do not change the value of the structure directly, unless you
are responsible for the result.  This ends up being the cause of interesting
bugs.

1.4 Convert C data into VALUE

To convert C data to Ruby values:

  * FIXNUM

    left shift 1 bit, and turn on LSB.

  * Other pointer values

    cast to VALUE.

You can determine whether a VALUE is pointer or not by checking its LSB.  

Notice Ruby does not allow arbitrary pointer values to be a VALUE.  They
should be pointers to the structures which Ruby knows about.  The known
structures are defined in <ruby.h>.

To convert C numbers to Ruby values, use these macros.

  INT2FIX()	for integers within 31bits.
  INT2NUM()	for arbitrary sized integer.

INT2NUM() converts an integer into a Bignum if it is out of the FIXNUM
range, but is a bit slower.

1.5 Manipulating Ruby data

As I already mentioned, it is not recommended to modify an object's internal
structure.  To manipulate objects, use the functions supplied by the Ruby
interpreter. Some (not all) of the useful functions are listed below:

 String functions

  rb_str_new(const char *ptr, long len)

    Creates a new Ruby string.

  rb_str_new2(const char *ptr)

    Creates a new Ruby string from a C string.  This is equivalent to
    rb_str_new(ptr, strlen(ptr)).

  rb_tainted_str_new(const char *ptr, long len)

    Creates a new tainted Ruby string.  Strings from external data
    sources should be tainted.

  rb_tainted_str_new2(const char *ptr)

    Creates a new tainted Ruby string from a C string.

  rb_str_cat(VALUE str, const char *ptr, long len)

    Appends len bytes of data from ptr to the Ruby string.

 Array functions

  rb_ary_new()

    Creates an array with no elements.

  rb_ary_new2(long len)

    Creates an array with no elements, allocating internal buffer
    for len elements.

  rb_ary_new3(long n, ...)

    Creates an n-element array from the arguments.

  rb_ary_new4(long n, VALUE *elts)

    Creates an n-element array from a C array.

  rb_ary_push(VALUE ary, VALUE val)
  rb_ary_pop(VALUE ary)
  rb_ary_shift(VALUE ary)
  rb_ary_unshift(VALUE ary, VALUE val)

    Array operations.  The first argument to each functions must be an 
    array.  They may dump core if other types given.

2. Extending Ruby with C

2.1 Addding new features to Ruby

You can add new features (classes, methods, etc.) to the Ruby
interpreter.  Ruby provides APIs for defining the following things:

 * Classes, Modules
 * Methods, Singleton Methods
 * Constants

2.1.1 Class/module definition

To define a class or module, use the functions below:

  VALUE rb_define_class(const char *name, VALUE super)
  VALUE rb_define_module(const char *name)

These functions return the newly created class or module.  You may
want to save this reference into a variable to use later.

To define nested classes or modules, use the functions below:

  VALUE rb_define_class_under(VALUE outer, const char *name, VALUE super)
  VALUE rb_define_module_under(VALUE outer, const char *name)

2.1.2 Method/singleton method definition

To define methods or singleton methods, use these functions:

  void rb_define_method(VALUE klass, const char *name, 
		        VALUE (*func)(), int argc)

  void rb_define_singleton_method(VALUE object, const char *name, 
			          VALUE (*func)(), int argc)

The `argc' represents the number of the arguments to the C function,
which must be less than 17.  But I believe you don't need that much. :-)

If `argc' is negative, it specifies the calling sequence, not number of
the arguments.  

If argc is -1, the function will be called as:

  VALUE func(int argc, VALUE *argv, VALUE obj)

where argc is the actual number of arguments, argv is the C array of
the arguments, and obj is the receiver.

If argc is -2, the arguments are passed in a Ruby array. The function
will be called like:

  VALUE func(VALUE obj, VALUE args)

where obj is the receiver, and args is the Ruby array containing
actual arguments.

There are two more functions to define methods.  One is to define
private methods:

  void rb_define_private_method(VALUE klass, const char *name, 
			        VALUE (*func)(), int argc)

The other is to define module functions, which are private AND singleton
methods of the module.  For example, sqrt is the module function
defined in Math module.  It can be call in the form like:

  Math.sqrt(4)

or

  include Math
  sqrt(4)

To define module functions, use:

  void rb_define_module_function(VALUE module, const char *name, 
				 VALUE (*func)(), int argc)

Oh, in addition, function-like methods, which are private methods defined
in the Kernel module, can be defined using:

  void rb_define_global_function(const char *name, VALUE (*func)(), int argc)

To define alias to the method,

  void rb_define_alias(VALUE module, const char* new, const char* old);

To define and undefine the `allocate' class method,

  void rb_define_alloc_func(VALUE klass, VALUE (*func)(VALUE klass));
  void rb_undef_alloc_func(VALUE klass);

func have to take the klass as the argument and return a newly
allocated instance.  This instance should be empty as possible,
without any expensive (including external) resources.

2.1.3 Constant definition

We have 2 functions to define constants:

  void rb_define_const(VALUE klass, const char *name, VALUE val)
  void rb_define_global_const(const char *name, VALUE val)

The former is to define a constant under specified class/module.  The
latter is to define a global constant.

2.2 Use Ruby features from C

There are several ways to invoke Ruby's features from C code.

2.2.1 Evaluate Ruby Programs in a String

The easiest way to use Ruby's functionality from a C program is to
evaluate the string as Ruby program.  This function will do the job.

  VALUE rb_eval_string(const char *str)

Evaluation is done under the current context, thus current local variables
of the innermost method (which is defined by Ruby) can be accessed.

2.2.2 ID or Symbol

You can invoke methods directly, without parsing the string.  First I
need to explain about symbols (whose data type is ID).  ID is the
integer number to represent Ruby's identifiers such as variable names.
It can be accessed from Ruby in the form:

 :Identifier

You can get the symbol value from a string within C code by using

  rb_intern(const char *name)

2.2.3 Invoke Ruby method from C

To invoke methods directly, you can use the function below

  VALUE rb_funcall(VALUE recv, ID mid, int argc, ...)

This function invokes a method on the recv, with the method name
specified by the symbol mid.

2.2.4 Accessing the variables and constants

You can access class variables and instance variables using access
functions.  Also, global variables can be shared between both environments.
There's no way to access Ruby's local variables.

The functions to access/modify instance variables are below:

  VALUE rb_ivar_get(VALUE obj, ID id)
  VALUE rb_ivar_set(VALUE obj, ID id, VALUE val)

id must be the symbol, which can be retrieved by rb_intern().

To access the constants of the class/module:

  VALUE rb_const_get(VALUE obj, ID id)

See 2.1.3 for defining new constant.

3. Information sharing between Ruby and C

3.1 Ruby constants that C can be accessed from C

The following Ruby constants can be referred from C.

  Qtrue
  Qfalse

Boolean values.  Qfalse is false in C also (i.e. 0).

  Qnil

Ruby nil in C scope.

3.2 Global variables shared between C and Ruby

Information can be shared between the two environments using shared global
variables.  To define them, you can use functions listed below:

  void rb_define_variable(const char *name, VALUE *var)

This function defines the variable which is shared by both environments.
The value of the global variable pointed to by `var' can be accessed
through Ruby's global variable named `name'.

You can define read-only (from Ruby, of course) variables using the
function below.

  void rb_define_readonly_variable(const char *name, VALUE *var)

You can defined hooked variables.  The accessor functions (getter and
setter) are called on access to the hooked variables.

  void rb_define_hooked_variable(constchar *name, VALUE *var,
				 VALUE (*getter)(), void (*setter)())

If you need to supply either setter or getter, just supply 0 for the
hook you don't need.  If both hooks are 0, rb_define_hooked_variable()
works just like rb_define_variable().

  void rb_define_virtual_variable(const char *name,
				  VALUE (*getter)(), void (*setter)())

This function defines a Ruby global variable without a corresponding C
variable.  The value of the variable will be set/get only by hooks.

The prototypes of the getter and setter functions are as follows:

  (*getter)(ID id, void *data, struct global_entry* entry);
  (*setter)(VALUE val, ID id, void *data, struct global_entry* entry);

3.3 Encapsulate C data into Ruby object

To wrap and objectify a C pointer as a Ruby object (so called
DATA), use Data_Wrap_Struct().

  Data_Wrap_Struct(klass, mark, free, ptr)

Data_Wrap_Struct() returns a created DATA object.  The klass argument
is the class for the DATA object.  The mark argument is the function
to mark Ruby objects pointed by this data.  The free argument is the
function to free the pointer allocation.  If this is -1, the pointer
will be just freed.  The functions mark and free will be called from
garbage collector.

You can allocate and wrap the structure in one step.

  Data_Make_Struct(klass, type, mark, free, sval)

This macro returns an allocated Data object, wrapping the pointer to
the structure, which is also allocated.  This macro works like:

  (sval = ALLOC(type), Data_Wrap_Struct(klass, mark, free, sval))

Arguments klass, mark, and free work like their counterparts in
Data_Wrap_Struct().  A pointer to the allocated structure will be
assigned to sval, which should be a pointer of the type specified.

To retrieve the C pointer from the Data object, use the macro
Data_Get_Struct().

  Data_Get_Struct(obj, type, sval)

A pointer to the structure will be assigned to the variable sval.

See the example below for details. 

4. Example - Creating dbm extension

OK, here's the example of making an extension library.  This is the
extension to access DBMs.  The full source is included in the ext/
directory in the Ruby's source tree.

(1) make the directory

  % mkdir ext/dbm

Make a directory for the extension library under ext directory.

(2) design the library

You need to design the library features, before making it.

(3) write C code.

You need to write C code for your extension library.  If your library
has only one source file, choosing ``LIBRARY.c'' as a file name is
preferred.  On the other hand, in case your library has multiple source
files, avoid choosing ``LIBRARY.c'' for a file name.  It may conflict
with an intermediate file ``LIBRARY.o'' on some platforms.

Ruby will execute the initializing function named ``Init_LIBRARY'' in
the library.  For example, ``Init_dbm()'' will be executed when loading
the library.

Here's the example of an initializing function.

--
Init_dbm()
{
    /* define DBM class */
    cDBM = rb_define_class("DBM", rb_cObject);
    /* DBM includes Enumerate module */
    rb_include_module(cDBM, rb_mEnumerable);

    /* DBM has class method open(): arguments are received as C array */
    rb_define_singleton_method(cDBM, "open", fdbm_s_open, -1);

    /* DBM instance method close(): no args */
    rb_define_method(cDBM, "close", fdbm_close, 0);
    /* DBM instance method []: 1 argument */
    rb_define_method(cDBM, "[]", fdbm_fetch, 1);
		:

    /* ID for a instance variable to store DBM data */
    id_dbm = rb_intern("dbm");
}
--

The dbm extension wraps the dbm struct in the C environment using 
Data_Make_Struct.

--
struct dbmdata {
    int  di_size;
    DBM *di_dbm;
};


obj = Data_Make_Struct(klass, struct dbmdata, 0, free_dbm, dbmp);
--

This code wraps the dbmdata structure into a Ruby object.  We avoid wrapping
DBM* directly, because we want to cache size information.

To retrieve the dbmdata structure from a Ruby object, we define the
following macro:

--
#define GetDBM(obj, dbmp) {\
    Data_Get_Struct(obj, struct dbmdata, dbmp);\
    if (dbmp->di_dbm == 0) closed_dbm();\
}
--

This sort of complicated macro does the retrieving and close checking for
the DBM.

There are three kinds of way to receive method arguments.  First,
methods with a fixed number of arguments receive arguments like this:

--
static VALUE
fdbm_delete(obj, keystr)
    VALUE obj, keystr;
{
	:
}
--

The first argument of the C function is the self, the rest are the
arguments to the method.

Second, methods with an arbitrary number of arguments receive
arguments like this:

--
static VALUE
fdbm_s_open(argc, argv, klass)
    int argc;
    VALUE *argv;
    VALUE klass;
{
	:
    if (rb_scan_args(argc, argv, "11", &file, &vmode) == 1) {
	mode = 0666;		/* default value */
    }
	:
}
--

The first argument is the number of method arguments, the second
argument is the C array of the method arguments, and the third
argument is the receiver of the method.

You can use the function rb_scan_args() to check and retrieve the
arguments.  For example, "11" means that the method requires at least one
argument, and at most receives two arguments.

Methods with an arbitrary number of arguments can receive arguments
by Ruby's array, like this:

--
static VALUE
fdbm_indexes(obj, args)
    VALUE obj, args;
{
	:
}
--

The first argument is the receiver, the second one is the Ruby array
which contains the arguments to the method.

** Notice

GC should know about global variables which refer to Ruby's objects, but
are not exported to the Ruby world.  You need to protect them by

  void rb_global_variable(VALUE *var)

(4) prepare extconf.rb

If the file named extconf.rb exists, it will be executed to generate
Makefile.

extconf.rb is the file for check compilation conditions etc.  You
need to put

  require 'mkmf'

at the top of the file.  You can use the functions below to check
various conditions.

  have_library(lib, func): check whether library containing function exists.
  have_func(func, header): check whether function exists
  have_header(header): check whether header file exists
  create_makefile(target): generate Makefile

The value of the variables below will affect the Makefile.

  $CFLAGS: included in CFLAGS make variable (such as -O)
  $CPPFLAGS: included in CPPFLAGS make variable (such as -I, -D)
  $LDFLAGS: included in LDFLAGS make variable (such as -L)
  $objs: list of object file names

In normal, object files list is automatically generated by searching
source files, but you need directs them explicitly if any sources will
be generated while building.

If a compilation condition is not fulfilled, you should not call
``create_makefile''.  The Makefile will not generated, compilation will
not be done.

(5) prepare depend (optional)

If the file named depend exists, Makefile will include that file to
check dependencies.  You can make this file by invoking

  % gcc -MM *.c > depend

It's no harm.  Prepare it.

(6) generate Makefile

Try generating the Makefile by:

  ruby extconf.rb

You don't need this step if you put the extension library under the ext
directory of the ruby source tree.  In that case, compilation of the
interpreter will do this step for you.

(7) make

Type

  make

to compile your extension.  You don't need this step either if you have
put extension library under the ext directory of the ruby source tree.

(8) debug

You may need to rb_debug the extension.  Extensions can be linked
statically by the adding directory name in the ext/Setup file so that
you can inspect the extension with the debugger.

(9) done, now you have the extension library

You can do anything you want with your library.  The author of Ruby
will not claim any restrictions on your code depending on the Ruby API.
Feel free to use, modify, distribute or sell your program.

Appendix A. Ruby source files overview

ruby language core

  class.c
  error.c
  eval.c
  gc.c
  object.c
  parse.y
  variable.c

utility functions

  dln.c
  regex.c
  st.c
  util.c

ruby interpreter implementation

  dmyext.c
  inits.c
  main.c
  ruby.c
  version.c

class library

  array.c
  bignum.c
  compar.c
  dir.c
  enum.c
  file.c
  hash.c
  io.c
  marshal.c
  math.c
  numeric.c
  pack.c
  prec.c
  process.c
  random.c
  range.c
  re.c
  signal.c
  sprintf.c
  string.c
  struct.c
  time.c

Appendix B. Ruby extension API reference

** Types

 VALUE

The type for the Ruby object.  Actual structures are defined in ruby.h,
such as struct RString, etc.  To refer the values in structures, use
casting macros like RSTRING(obj).

** Variables and constants

 Qnil

const: nil object

 Qtrue

const: true object(default true value)

 Qfalse

const: false object

** C pointer wrapping

 Data_Wrap_Struct(VALUE klass, void (*mark)(), void (*free)(), void *sval)

Wrap a C pointer into a Ruby object.  If object has references to other
Ruby objects, they should be marked by using the mark function during
the GC process.  Otherwise, mark should be 0.  When this object is no
longer referred by anywhere, the pointer will be discarded by free
function.

 Data_Make_Struct(klass, type, mark, free, sval)

This macro allocates memory using malloc(), assigns it to the variable
sval, and returns the DATA encapsulating the pointer to memory region.

 Data_Get_Struct(data, type, sval)

This macro retrieves the pointer value from DATA, and assigns it to
the variable sval. 

** Checking data types

TYPE(value)
FIXNUM_P(value)
NIL_P(value)
void Check_Type(VALUE value, int type)
void Check_SafeStr(VALUE value)

** Data type conversion

FIX2INT(value)
INT2FIX(i)
NUM2INT(value)
INT2NUM(i)
NUM2DBL(value)
rb_float_new(f)
StringValue(value)
StringValuePtr(value)
StringValueCStr(value)
rb_str_new2(s)

** defining class/module

 VALUE rb_define_class(const char *name, VALUE super)

Defines a new Ruby class as a subclass of super.

 VALUE rb_define_class_under(VALUE module, const char *name, VALUE super)

Creates a new Ruby class as a subclass of super, under the module's
namespace.

 VALUE rb_define_module(const char *name)

Defines a new Ruby module.

 VALUE rb_define_module_under(VALUE module, const char *name)

Defines a new Ruby module under the module's namespace.

 void rb_include_module(VALUE klass, VALUE module)

Includes module into class.  If class already includes it, just
ignored.

 void rb_extend_object(VALUE object, VALUE module)

Extend the object with the module's attributes.

** Defining Global Variables

 void rb_define_variable(const char *name, VALUE *var)

Defines a global variable which is shared between C and Ruby.  If name
contains a character which is not allowed to be part of the symbol,
it can't be seen from Ruby programs.

 void rb_define_readonly_variable(const char *name, VALUE *var)

Defines a read-only global variable.  Works just like
rb_define_variable(), except defined variable is read-only.

 void rb_define_virtual_variable(const char *name,
				 VALUE (*getter)(), VALUE (*setter)())

Defines a virtual variable, whose behavior is defined by a pair of C
functions.  The getter function is called when the variable is
referred.  The setter function is called when the value is set to the
variable.  The prototype for getter/setter functions are:

	VALUE getter(ID id)
	void setter(VALUE val, ID id)

The getter function must return the value for the access.

 void rb_define_hooked_variable(const char *name, VALUE *var,
				VALUE (*getter)(), VALUE (*setter)())

Defines hooked variable.  It's a virtual variable with a C variable.  
The getter is called as

	VALUE getter(ID id, VALUE *var)

returning a new value.  The setter is called as

	void setter(VALUE val, ID id, VALUE *var)

GC requires C global variables which hold Ruby values to be marked.

 void rb_global_variable(VALUE *var)

Tells GC to protect these variables.

** Constant Definition

 void rb_define_const(VALUE klass, const char *name, VALUE val)

Defines a new constant under the class/module.

 void rb_define_global_const(const char *name, VALUE val)

Defines a global constant.  This is just the same as

     rb_define_const(cKernal, name, val)

** Method Definition

 rb_define_method(VALUE klass, const char *name, VALUE (*func)(), int argc)

Defines a method for the class.  func is the function pointer.  argc
is the number of arguments.  if argc is -1, the function will receive
3 arguments: argc, argv, and self.  if argc is -2, the function will
receive 2 arguments, self and args, where args is a Ruby array of
the method arguments.

 rb_define_private_method(VALUE klass, const char *name, VALUE (*func)(), int argc)

Defines a private method for the class.  Arguments are same as
rb_define_method().

 rb_define_singleton_method(VALUE klass, const char *name, VALUE (*func)(), int argc)

Defines a singleton method.  Arguments are same as rb_define_method().

 rb_scan_args(int argc, VALUE *argv, const char *fmt, ...)

Retrieve argument from argc, argv.  The fmt is the format string for
the arguments, such as "12" for 1 non-optional argument, 2 optional
arguments.  If `*' appears at the end of fmt, it means the rest of
the arguments are assigned to the corresponding variable, packed in
an array.

** Invoking Ruby method

 VALUE rb_funcall(VALUE recv, ID mid, int narg, ...)

Invokes a method.  To retrieve mid from a method name, use rb_intern().

 VALUE rb_funcall2(VALUE recv, ID mid, int argc, VALUE *argv)

Invokes a method, passing arguments by an array of values.

 VALUE rb_eval_string(const char *str)

Compiles and executes the string as a Ruby program.

 ID rb_intern(const char *name)

Returns ID corresponding to the name.

 char *rb_id2name(ID id)

Returns the name corresponding ID.

 char *rb_class2name(VALUE klass)

Returns the name of the class.

 int rb_respond_to(VALUE object, ID id)

Returns true if the object responds to the message specified by id.

** Instance Variables

 VALUE rb_iv_get(VALUE obj, const char *name)

Retrieve the value of the instance variable.  If the name is not
prefixed by `@', that variable shall be inaccessible from Ruby.

 VALUE rb_iv_set(VALUE obj, const char *name, VALUE val)

Sets the value of the instance variable.

** Control Structure

 VALUE rb_iterate(VALUE (*func1)(), void *arg1, VALUE (*func2)(), void *arg2)

Calls the function func1, supplying func2 as the block.  func1 will be
called with the argument arg1.  func2 receives the value from yield as
the first argument, arg2 as the second argument.
 
 VALUE rb_yield(VALUE val)

Evaluates the block with value val.

 VALUE rb_rescue(VALUE (*func1)(), void *arg1, VALUE (*func2)(), void *arg2)

Calls the function func1, with arg1 as the argument.  If an exception
occurs during func1, it calls func2 with arg2 as the argument.  The
return value of rb_rescue() is the return value from func1 if no
exception occurs, from func2 otherwise.

 VALUE rb_ensure(VALUE (*func1)(), void *arg1, void (*func2)(), void *arg2)

Calls the function func1 with arg1 as the argument, then calls func2
with arg2 if execution terminated.  The return value from
rb_ensure() is that of func1.

** Exceptions and Errors

 void rb_warn(const char *fmt, ...)

Prints a warning message according to a printf-like format.

 void rb_warning(const char *fmt, ...)

Prints a warning message according to a printf-like format, if
$VERBOSE is true.

void rb_raise(rb_eRuntimeError, const char *fmt, ...)

Raises RuntimeError.  The fmt is a format string just like printf().

 void rb_raise(VALUE exception, const char *fmt, ...)

Raises a class exception.  The fmt is a format string just like printf().

 void rb_fatal(const char *fmt, ...)

Raises a fatal error, terminates the interpreter.  No exception handling
will be done for fatal errors, but ensure blocks will be executed.

 void rb_bug(const char *fmt, ...)

Terminates the interpreter immediately.  This function should be
called under the situation caused by the bug in the interpreter.  No
exception handling nor ensure execution will be done.

** Initialize and Starts the Interpreter

The embedding API functions are below (not needed for extension libraries):

 void ruby_init()

Initializes the interpreter.

 void ruby_options(int argc, char **argv)

Process command line arguments for the interpreter.

 void ruby_run()

Starts execution of the interpreter.

 void ruby_script(char *name)

Specifies the name of the script ($0).

Appendix C. Functions Available in extconf.rb

These functions are available in extconf.rb:

 have_macro(macro, headers)

Checks whether macro is defined with header.  Returns true if the macro
is defined.

 have_library(lib, func)

Checks whether the library exists, containing the specified function.
Returns true if the library exists.

 find_library(lib, func, path...)

Checks whether a library which contains the specified function exists in
path.  Returns true if the library exists.

 have_func(func, header)

Checks whether func exists with header.  Returns true if the function
exists.  To check functions in an additional library, you need to
check that library first using have_library().

 have_var(var, header)

Checks whether var exists with header.  Returns true if the variable
exists.  To check variables in an additional library, you need to
check that library first using have_library().

 have_header(header)

Checks whether header exists.  Returns true if the header file exists.

 find_header(header, path...)

Checks whether header exists in path.  Returns true if the header file
exists.

 have_struct_member(type, member, header)

Checks whether type has member with header.  Returns true if the type
is defined and has the member.

 have_type(type, header, opt)

Checks whether type is defined with header.  Returns true if the type
is defined.

 check_sizeof(type, header)

Checks the size of type in char with header.  Returns the size if the
type is defined, otherwise nil.

 create_makefile(target)

Generates the Makefile for the extension library.  If you don't invoke
this method, the compilation will not be done.

 find_executable(bin, path)

Finds command in path, which is File::PATH_SEPARATOR-separated list of
directories.  If path is nil or omitted, environment varialbe PATH
will be used.  Returns the path name of the command if it is found,
otherwise nil.

 with_config(withval[, default=nil])

Parses the command line options and returns the value specified by
--with-<withval>.

 enable_config(config, *defaults)
 disable_config(config, *defaults)

Parses the command line options for boolean.  Returns true if
--enable-<config> is given, or false if --disable-<config> is given.
Otherwise, yields defaults to the given block and returns the result
if it is called with a block, or returns defaults.

 dir_config(target[, default_dir])
 dir_config(target[, default_include, default_lib])

Parses the command line options and adds the directories specified by
--with-<target>-dir, --with-<target>-include, and/or --with-<target>-lib
to $CFLAGS and/or $LDFLAGS.  --with-<target>-dir=/path is equivalent to
--with-<target>-include=/path/include --with-<target>-lib=/path/lib.
Returns an array of the added directories ([include_dir, lib_dir]).

 pkg_config(pkg)

Obtains the information of pkg by pkg-config command.  The actual
command name can be overriden by --with-pkg-config command line
option.

/*
 * Local variables:
 * fill-column: 70
 * end:
 */