It
is easy to extend Ruby with new features by writing code in Ruby.
Once you start adding in low-level code written in C, however, the
possibilities are endless.
Extending Ruby with C is pretty easy. For instance, suppose we are
building a custom Internet-ready jukebox for the Sunset Diner and
Grill. It will play MP3 audio files from a hard disk or audio CDs
from a CD jukebox. We want to be able to control the jukebox hardware
from a Ruby program. The hardware vendor gave us a C header file and
a binary library to use; our job is to construct a Ruby object
that makes the appropriate C function calls.
But before we can get Ruby and C to work together, we need to see what
the Ruby world looks like from the C side.[Much of the
information in this chapter is taken from the README.EXT
file that is included in the distribution. If you are planning on
writing a Ruby extension, you may want to refer to that file for
more details as well as the latest changes.]
The first thing we need to look at is how to represent and access Ruby
datatypes from within C.
Everything in Ruby is an object, and all
variables are references to objects. In C, this means that the type
of all Ruby variables is VALUE,
which is either a pointer to a Ruby object or an immediate value (such
as Fixnum).
This is how Ruby implements object-oriented code in C: a Ruby object
is an allocated structure in memory that contains a table of instance
variables and information about the class. The class itself is
another object (an allocated structure in memory) that contains a
table of the methods defined for that class. On this foundation hangs
all of Ruby.
When VALUE is a pointer, it is a pointer to one of the
defined Ruby object structures---you can't have a VALUE that points to an
arbitrary structure. The structures for each built-in
class are defined in ``ruby.h''
and are named RClassname, as in RString and
RArray.
You can check to see what type of structure is used for a particular
VALUE in a number of ways. The macro TYPE(obj)
will return a constant representing the C
type of the given object: T_OBJECT, T_STRING, and so on.
Constants for the built-in classes are defined in ``ruby.h''.
Note that the type we are referring to here is an
implementation detail---it is not the same as the class of an object.
If you want to ensure that a value pointer points to a particular
structure, you can use the macro Check_Type, which will raise a
TypeError exception if value is not of the expected
type (which is one of the constants T_STRING,
T_FLOAT, and so on):
Check_Type(VALUE value, int type)
If speed is an issue, there are faster macros that check specifically
for the immediate values Fixnum and nil.
FIXNUM_P(value) -> non-zero if value is a Fixnum
NIL_P(value) -> non-zero if value is nil
RTEST(value) -> non-zero if value is neither nil nor false
Again, note that we are talking about ``type'' as the C structure that
represents a particular built-in type. The class of an object is a
different beast entirely. The class objects for the built-in classes
are stored in C global variables named rb_cClassname
(for instance, rb_cObject); modules are named
rb_mModulename.
It wouldn't be advisable to mess with the data in these
structures directly, however---you may look, but don't touch unless
you are fond of debuggers. You should normally use only the supplied
C functions to manipulate Ruby data (we'll talk more about this in just
a moment).
However, in the interests of efficiency you may need to dig into these
structures to obtain data. In order to dereference members of these C
structures, you have to cast the generic VALUE to the proper
structure type. ruby.h contains a number of macros that perform
the proper casting for you, allowing you to dereference structure
members easily. These macros are named
RCLASSNAME, as in RSTRING or RARRAY. For
example:
VALUE str, arr;
RSTRING(str)->len -> length of the Ruby string
RSTRING(str)->ptr -> pointer to string storage
RARRAY(arr)->len -> length of the Ruby array
RARRAY(arr)->capa -> capacity of the Ruby array
RARRAY(arr)->ptr -> pointer to array storage
As we said above, immediate values are not pointers: Fixnum,
Symbol, true, false, and nil are stored directly in
VALUE.
Fixnum values are stored as 31-bit numbers[Or 63-bit on
wider CPU architectures.] that are formed by shifting the original
number left 1 bit and then setting the least significant bit (bit
0) to ``1.'' When VALUE is used as a pointer to a specific Ruby
structure, it is guaranteed always to have an LSB of zero; the
other immediate values also have LSBs of zero. Thus, a simple
bit test can tell you whether or not you have a Fixnum.
There are several useful conversion macros for numbers as well as
other standard datatypes shown in Table 17.1 on page 174.
The other immediate values (true, false, and nil) are
represented in C as the constants Qtrue, Qfalse, and
Qnil, respectively. You can test VALUE variables against
these constants directly, or use the conversion macros (which perform
the proper casting).
One of the joys of Ruby is that you can write Ruby programs almost
directly in C. That is, you can use the same methods and the same
logic, but with slightly different syntax to accommodate C. For
instance, here is a small, fairly boring test class written in Ruby.
class Test
def initialize
@arr = Array.new
end
def add(anObject)
@arr.push(anObject)
end
end
The equivalent code in C should look somewhat familiar.
#include "ruby.h"
static VALUE t_init(VALUE self)
{
VALUE arr;
arr = rb_ary_new();
rb_iv_set(self, "@arr", arr);
return self;
}
static VALUE t_add(VALUE self, VALUE anObject)
{
VALUE arr;
arr = rb_iv_get(self, "@arr");
rb_ary_push(arr, anObject);
return arr;
}
VALUE cTest;
void Init_Test() {
cTest = rb_define_class("Test", rb_cObject);
rb_define_method(cTest, "initialize", t_init, 0);
rb_define_method(cTest, "add", t_add, 1);
}
Let's go through this example in detail, as it illustrates many of the
important concepts in this chapter. First off, we need to include the
header file ``ruby.h'' to obtain the necessary definitions.
Now look at the last function, Init_Test.
Every class or module
defines a C global function named Init_Name. This
function will be called when the interpreter first loads the extension
Name (or on startup for statically linked extensions). It is
used to initialize the extension and to insinuate it into the Ruby
environment. In this case, we define a new class named Test,
which is a subclass of Object (represented by the external symbol
rb_cObject; see ``ruby.h'' for others).
Next we set up add and initialize as two instance methods
for class Test.
The calls to rb_define_method establish
a binding between the Ruby method name and the C function that will
implement it, so a call to the add method in Ruby will call the
C function t_add with one argument.
Similarly, when new is called for this class, Ruby will construct
a basic object and then call initialize, which we have defined
here to call the C function t_init with no (Ruby) arguments.
Now go back and look at the definition of initialize. Even
though we said it took no arguments, there's a parameter here! In
addition to any Ruby arguments, every method is passed an initial
VALUE argument that contains the receiver for this method (the
equivalent of self in Ruby code).
The first thing we'll do in initialize is create a Ruby array
and set the instance variable @arr to point to it. Just as you
would expect if you were writing Ruby source, referencing an instance
variable that doesn't exist creates it.
Finally, the function t_add gets the instance variable @arr
from the current object and calls Array#push to push the passed value
onto that array. When accessing instance variables in this way, the
@-prefix is mandatory---otherwise the variable is created, but
cannot be referenced from Ruby.
Despite the extra, clunky syntax that C imposes, you're still writing
in Ruby---you can manipulate objects using all of the method calls
you've come to know and love, with the added advantage of being able
to craft tight, fast code when needed.
WARNING: Every C function that is callable from Ruby
must return a VALUE, even if it's just Qnil.
Otherwise, a core dump (or GPF) will be the likely result.
We can use the C version of the code in Ruby simply
by require-ing it dynamically at runtime (on
most platforms).
require "code/ext/Test"
t = Test.new
t.add("Bill Chase")
If you are in the middle of some C code and you want to run an
arbitrary Ruby expression without writing a bunch of C, you can always
use the C version of eval. Suppose you have a collection of
objects that need to have a flag cleared.
We've covered enough of the basics now to return to our jukebox
example---interfacing C code with Ruby and sharing data and behavior
between the two worlds.
Although you could maintain a C version of some variable along with a
separate Ruby version of that variable, and struggle to keep the two
in sync,[A clear violation of the DRY--Don't
Repeat Yourself---principle described in our book The Pragmatic
Programmer .] it would be much better to
share a variable directly between Ruby and C.
You can share global
variables by creating a Ruby object on the C side and then binding
its address to a Ruby global variable. In this case, the $ prefix is
optional, but it helps clarify that this is a global variable.
The Ruby side can then access the C variable hardware_list as
$hardware:
$hardware
»
["DVD", "CDPlayer1", "CDPlayer2"]
You can also create hooked
variables that will call a specified function when the variable is
accessed, and virtual variables that only call the hooks---no
actual variable is involved. See the API section that begins
on page 189 for details.
If you create a Ruby object from C and store it in a C global
variable
without exporting it to Ruby, you must at least tell the
garbage collector about it, lest ye be reaped inadvertently:
VALUE obj;
obj = rb_ary_new();
rb_global_variable(obj);
Now on to the really fun stuff. We've got the vendor's
library that controls the audio CD jukebox units, and we're ready to
wire it into Ruby. The vendor's header file looks like this:
typedef struct _cdjb {
int statusf;
int request;
void *data;
char pending;
int unit_id;
void *stats;
} CDJukebox;
// Allocate a new CDPlayer structure and bring it online
CDJukebox *CDPlayerNew(int unit_id);
// Deallocate when done (and take offline)
void CDPlayerDispose(CDJukebox *rec);
// Seek to a disc, track and notify progress
void CDPlayerSeek(CDJukebox *rec,
int disc,
int track,
void (*done)(CDJukebox *rec, int percent));
// ... others...
// Report a statistic
double CDPlayerAvgSeekTime(CDJukebox *rec);
This vendor has its act together; while the vendor might not admit it, the
code is written with an object-oriented flavor. We don't know what
all those fields mean within the CDJukeBox structure, but that's
okay---we can treat it as an opaque pile of bits. The vendor's code
knows what to do with it, we just have to carry it around.
Anytime you have a C-only structure that you would like to handle as a
Ruby object, you should wrap it in a special, internal Ruby class
called DATA (type T_DATA).
There are two macros to do this wrapping, and one to retrieve your
structure back out again.
Wraps the given C datatype ptr, registers the
two garbage collection routines (see below), and returns
a VALUE pointer to a genuine Ruby object. The C type of the
resulting object is T_DATA and its Ruby class is class.
Allocates a structure of the indicated
type first, then proceeds as Data_Wrap_Struct. c-type
is the name of the C datatype that you're wrapping, not a
variable of that type.
Data_Get_Struct(VALUE obj,c-type,c-type *")
Returns the original pointer. This macro
is a type-safe wrapper around the macro
DATA_PTR(obj), which evaluates the pointer.
The object created by Data_Wrap_Struct is a normal Ruby object,
except that it has an additional C datatype that can't be accessed
from Ruby. As you can see in Figure 17.1 on page 177, this C
datatype is separate from any instance variables that the object
contains.
But since it's a separate thing, how do you get rid of it when the
garbage collector claims this object? What if you have to release
some resource (close some file, clean up some lock or IPC mechanism,
and so on)?
Figure not available...
In order to participate in Ruby's mark-and-sweep garbage collection process,
you need to define a
routine to free your structure, and possibly a routine to mark any
references from your structure to other structures. Both routines take a void
pointer, a reference to your structure.
The mark routine will be called by the garbage collector
during its ``mark'' phase. If your structure references other Ruby
objects, then your mark function needs to identify these objects using
rb_gc_mark(value). If the structure doesn't reference
other Ruby objects, you can simply pass 0 as a function pointer.
When the object needs to be disposed of, the garbage collector will
call the free routine to free it. If you have allocated any
memory yourself (for instance, by using Data_Make_Struct),
you'll need to pass a free function---even if it's just the standard C
library's free routine. For complex structures that you have
allocated, your free function may need to traverse the structure to
free all the allocated memory.
First a simple example, without any special handling. Given the
structure definition
we can create a structure, populate it, and wrap it as an
object.[We cheat a bit in this example. Our MP3Info
structure has a couple of char pointers in it. In our code we
initialize them from two static strings. This means that we don't
have to free these strings when the MP3Info structure is freed.
If we'd allocated these strings dynamically, we'd have to write a
free method to dispose of them.]
MP3Info *p;
VALUE info;
p = ALLOC(MP3Info);
p->artist = "Maynard Ferguson";
p->title = "Chameleon";
...
info = Data_Wrap_Struct(cTest, 0, free, p);
info is a VALUE type, a genuine Ruby object of class
Test (represented in C by the built-in type T_DATA). You
can push it onto an array, hold a reference to it in an object, and so
on. At some later point in the code, we may want to access this
structure again, given the VALUE:
In order to follow convention, however, you may need a few more
things: support for an initialize method, and
a ``C-constructor.'' If you
were writing Ruby source, you'd allocate and initialize an object by
calling new. In C extensions, the corresponding call is
Data_Make_Struct. However, although this allocates memory for
the object, it does not automatically call an initialize
method; you need to do that yourself:
info = Data_Make_Struct(cTest, MP3Info, 0, free, one);
rb_obj_call_init(info, argc, argv);
This has the benefit of allowing subclasses in Ruby to override or
augment the basic initialize in your class. Within
initialize, it is allowable (but not necessarily advisable) to
alter the existing data pointer, which may be accessed directly with
DATA_PTR(obj).
And finally, you may want to define a ``C-constructor''---that
is, a globally available C function that will
create the object in one convenient call. You can use this function
within your own code or allow other extension libraries to use it.
All of the built-in classes support this idea with functions such as
rb_str_new, rb_ary_new, and so on. We can make our own:
VALUE mp3_info_new() {
VALUE info;
MP3Info *one;
info = Data_Make_Struct(cTest, MP3Info, 0, free, one);
...
rb_obj_call_init(info, 0, 0);
return info;
}
Okay, now we're ready for a full-size example.
Given our vendor's header file above, we write the following code.
#include "ruby.h"
#include "cdjukebox.h"
VALUE cCDPlayer;
static void cd_free(void *p) {
CDPlayerDispose(p);
}
static void progress(CDJukebox *rec, int percent)
{
if (rb_block_given_p()) {
if (percent > 100) percent = 100;
if (percent < 0) percent = 0;
rb_yield(INT2FIX(percent));
}
}
static VALUE
cd_seek(VALUE self, VALUE disc, VALUE track)
{
CDJukebox *ptr;
Data_Get_Struct(self, CDJukebox, ptr);
CDPlayerSeek(ptr,
NUM2INT(disc),
NUM2INT(track),
progress);
return Qnil;
}
static VALUE
cd_seekTime(VALUE self)
{
double tm;
CDJukebox *ptr;
Data_Get_Struct(self, CDJukebox, ptr);
tm = CDPlayerAvgSeekTime(ptr);
return rb_float_new(tm);
}
static VALUE
cd_unit(VALUE self)
{
return rb_iv_get(self, "@unit");
}
static VALUE
cd_init(VALUE self, VALUE unit)
{
rb_iv_set(self, "@unit", unit);
return self;
}
VALUE cd_new(VALUE class, VALUE unit)
{
VALUE argv[1];
CDJukebox *ptr = CDPlayerNew(NUM2INT(unit));
VALUE tdata = Data_Wrap_Struct(class, 0, cd_free, ptr);
argv[0] = unit;
rb_obj_call_init(tdata, 1, argv);
return tdata;
}
void Init_CDJukebox() {
cCDPlayer = rb_define_class("CDPlayer", rb_cObject);
rb_define_singleton_method(cCDPlayer, "new", cd_new, 1);
rb_define_method(cCDPlayer, "initialize", cd_init, 1);
rb_define_method(cCDPlayer, "seek", cd_seek, 2);
rb_define_method(cCDPlayer, "seekTime", cd_seekTime, 0);
rb_define_method(cCDPlayer, "unit", cd_unit, 0);
}
Now we have the ability to control our jukebox from Ruby in a nice,
object-oriented manner:
require "code/ext/CDJukebox"
p = CDPlayer.new(1)
puts "Unit is #{p.unit}"
p.seek(3, 16) {|x| puts "#{x}% done" }
puts "Avg. time was #{p.seekTime} seconds"
produces:
Unit is 1
26% done
79% done
100% done
Avg. time was 1.2 seconds
This example demonstrates most of what we've talked about so far, with
one additional neat feature. The vendor's library provided a callback
routine---a function pointer that is called every so often while the
hardware is grinding its way to the next disc. We've set that up here
to run a code block passed as an argument to seek. In the
progress function, we check to see if there is an iterator in the
current context and, if there is, run it
with the current percent done as an argument.
You may sometimes need to allocate memory in an extension that
won't be used for object storage---perhaps you've got a giant bitmap
for a Bloom filter, or an image, or a whole bunch of little structures
that Ruby doesn't use directly.
In order to work correctly with the garbage collector, you should use
the following memory allocation routines. These routines do a little
bit more work than the standard malloc. For instance, if
ALLOC_N determines that it cannot allocate the desired amount of
memory, it will invoke the garbage collector to try to reclaim some
space. It will raise a
NoMemError if it can't or if the requested amount of memory is
invalid.
Memory Allocation
type *
ALLOC_N(c-type, n")
Allocates nc-type objects, where c-type is
the literal name of the C type, not a variable of that type.
type *
ALLOC(c-type")
Allocates a c-type and casts the result to a pointer of
that type.
REALLOC_N(var, c-type, n")
Reallocates nc-types and assigns the result to var,
a pointer to a c-type.
type *
ALLOCA_N(c-type, n")
Allocates memory for n objects of c-type on the
stack---this memory will be automatically freed when the function
that invokes ALLOCA_N returns.
Having written the source code for an extension, we now need to compile
it so Ruby can use it. We can either do this as a shared
object, which is dynamically loaded at runtime, or statically link
the extension into the main Ruby interpreter itself. The basic
procedure is the same:
Create the C source code file(s) in a given directory.
Create extconf.rb.
Run extconf.rb to create a Makefile for the C files in
this directory.
Figure 17.2 on page 182 shows the overall workflow when building an
extension.
The key to the whole process is the extconf.rb
program which you, as a developer, create. In extconf.rb, you
write a simple program that determines what features are available on
the user's system and where those features may be located. Executing
extconf.rb builds a customized
Makefile, tailored for both your application and the system on
which it's being compiled. When you run the make command against
this Makefile, your extension is built and (optionally) installed.
The simplest extconf.rb may be just two lines long, and for many
extensions this is sufficient.
require 'mkmf'
create_makefile("Test")
The first line brings in the mkmf library module
(documented beginning on page 451). This contains all the
commands we'll be using. The second line creates a Makefile for an
extension called ``Test.'' (Note that ``Test'' is the name of the
extension; the makefile will always be called ``Makefile.'')
Test will be built from all the C source files in the
current directory.
Let's say that we run this extconf.rb program in a directory
containing a single source file, main.c. The
result is a Makefile that will build our extension. On our system,
this contains the following commands.
The result of this compilation is Test.so, which may be
dynamically linked into Ruby at runtime with ``require''. See how
the mkmf commands have located platform-specific libraries and
used compiler-specific options automatically. Pretty neat, eh?
Although this basic program works for many simple extensions, you may
have to do some more work if your extension needs header files or
libraries that aren't included in the default compilation environment,
or if you conditionally compile code based on the presence of
libraries or functions.
A common requirement is to specify nonstandard directories where
include files and libraries may be found. This is a two-step process.
First, your extconf.rb should contain one or more
dir_config commands.
This specifies a tag for a set of directories. Then, when you run the
extconf.rb program, you tell mkmf where the corresponding
physical directories are on the current system.
If extconf.rb contains the line dir_config(name),
then you give the location of the corresponding directories with the
command-line options:
--with-name-include=directory
*
Add directory/include to the compile command.
--with-name-lib=directory
*
Add directory/lib to the link command.
If (as is common) your include and library directories are both
subdirectories of some other directory, and (as is also common) they're
called include and lib, you can take a shortcut:
--with-name-dir=directory
*
Add directory/lib and directory/include to the link
command and compile command, respectively.
There's a twist here. As well as specifying all these --with
options when you run extconf.rb, you can also use the --with
options that were specified when Ruby was built for your machine. This
means you can find out the locations of libraries that are used by
Ruby itself.
To make all this concrete, lets say you need to use libraries and
include files for the CD jukebox we're developing. Your
extconf.rb program might contain
require 'mkmf'
dir_config('cdjukebox')
# .. more stuff
create_makefile("CDJukeBox")
The generated Makefile would assume that the libraries were in
/usr/local/cdjb/lib and the include files were in
/usr/local/cdjb/include.
The dir_config command adds to the list of places to search
for libraries and include files. It does not, however, link the
libraries into your application. To do that, you'll need to use one
or more have_library or find_library commands.
have_library looks for
a given entry point in a named library. If it finds the entry point,
it adds the library to the list of libraries to be used when linking
your extension.
find_library is
similar, but allows you to specify a list of directories to search for
the library.
On some platforms, a popular library may be in one of several places.
The X Window system, for example, is notorious for living in different
directories on different systems. The find_library command will
search a list of supplied directories to find the right one (this is
different from have_library, which uses only configuration
information for the search). For example, to create a Makefile
that uses X Windows and a jpeg library, extconf.rb might contain
require 'mkmf'
if have_library("jpeg","jpeg_mem_init") and
find_library("X11", "XOpenDisplay", "/usr/X11/lib",
"/usr/X11R6/lib", "/usr/openwin/lib")
then
create_makefile("XThing")
else
puts "No X/JPEG support available"
end
We've added some additional functionality to this program. All of the
mkmf commands return false if they fail. This means that
we can write an extconf.rb that generates a Makefile only if
everything it needs is present. The Ruby distribution does
this so that it will try to compile only those extensions that are supported
on your system.
You also may want your extension code to be able to configure the
features it uses depending on the target environment. For example, our
CD jukebox may be able to use a high-performance MP3 decoder if the
end user has one installed. We can check by looking for its header
file.
We can also check to see if the target environment has a particular
function in any of the libraries we'll be using. For example, the
setpriority call would be useful but isn't always
available. We can check for it with:
Both have_header and have_func define
preprocessor constants if they find their targets. The names are
formed by converting the target name to uppercase and prepending
``HAVE_''. Your C code can take advantage of this using constructs
such as:
If you have special requirements that can't be met with all
these mkmf commands, your program can directly add to the global
variables $CFLAGS and $LFLAGS, which are passed to the
compiler and linker, respectively.
Finally, if your system doesn't support dynamic linking, or if you
have an extension module that you want to have statically linked into
Ruby itself, edit the file ext/Setup in
the distribution and add your directory to the list of extensions in
the file, then rebuild Ruby.
The extensions listed in Setup will be
statically linked into the Ruby executable. If you want to disable
any dynamic linking, and link all extensions statically, edit
ext/Setup to contain the following option.
See main.c in the Ruby distribution for any other special defines
or setup needed for your platform.
Embedded Ruby API
void
ruby_init(")
Sets up and initializes the interpreter. This function should be
called before any other Ruby-related functions.
void
ruby_options(int argc, char **argv")
Gives the Ruby interpreter the command-line options.
void
ruby_script(char *name")
Sets the name of the Ruby script (and $0) to name.
void
rb_load_file(char *file")
Loads the given file into the interpreter.
void
ruby_run(")
Runs the interpreter.
You need to take some special care with exception handling; any Ruby
calls you make at this top level should be protected to catch
exceptions and handle them cleanly. rb_protect, rb_rescue, and related
functions are documented on page 192.
For an example of embedding a Ruby interpreter within another program,
see also eruby, which is described beginning on page 147.
So far, we've discussed extending Ruby by adding routines written in C.
However, you can write extensions in just about any language, as long
as you can bridge the two languages with C. Almost anything is
possible, including awkward marriages of Ruby and C++, Ruby and Java,
and so on.
But you may be able to accomplish the same thing without resorting to C
code. For example, you could bridge to other languages using
middleware such as CORBA or COM. See the section on Windows automation
beginning on page 164 for more details.
Last, but by no means least, here are several C-level functions
that you may find useful when writing an extension.
Some functions require an ID: you can
obtain an ID for a string by using rb_intern and
reconstruct the name from an ID by using rb_id2name.
As most of these C functions have Ruby equivalents that are already
described in detail elsewhere in this book, the descriptions here will
be brief.
Also note that the following listing is not complete. There are many more
functions available---too many to document them all, as it turns out.
If you need a method that you can't find here, check ``ruby.h'' or
``intern.h'' for likely candidates. Also, at or near the bottom
of each source file is a set of method definitions that describe the
binding from Ruby methods to C functions. You may be able to call the
C function directly, or search for a wrapper function that calls the
function you are looking for. The following list, based on the list
in README.EXT, shows the main source
files in the interpreter.
Defines a new class at the top level with the given name and
superclass (for class Object, use rb_cObject).
VALUE
rb_define_module(char *name")
Defines a new module at the top level with the given name.
VALUE
rb_define_class_under(VALUE under, char *name,
VALUE superclass")
Defines a nested class under the class or module under.
VALUE
rb_define_module_under(VALUE under, char *name")
Defines a nested module under the class or module under.
void
rb_include_module(VALUE parent, VALUE module")
Includes the given module into the class or module
parent.
void
rb_extend_object(VALUE obj, VALUE module")
Extends obj with module.
VALUE
rb_require(const char *name")
Equivalent to ``requirename.''
Returns Qtrue or Qfalse.
In some of the function definitions that follow, the parameter
argc specifies how many arguments a Ruby method takes. It
may have the following values.
argc
Function prototype
0..17
VALUE func(VALUE self, VALUE arg...)
The C function will be called with this many actual arguments.
-1
VALUE func(int argc, VALUE *argv, VALUE self)
The C function will be given a variable number of arguments passed
as a C array.
-2
VALUE func(VALUE self, VALUE args)
The C function will be given a variable number of arguments
passed as a Ruby array.
In a function that has been given a variable number of arguments,
you can use the C function rb_scan_args to sort things out (see below).
Defining Methods
void
rb_define_method(VALUE classmod, char *name,
VALUE(*func)(), int argc")
Defines an instance method in the class or module classmod with the given name, implemented
by the C function func and taking argc arguments.
void
rb_define_module_function(VALUE classmod, char *name,
VALUE(*func)(), int argc)")
Defines a method in class classmod with the given name, implemented
by the C function func and taking argc arguments.
void
rb_define_global_function(char *name, VALUE(*func)(),
int argc")
Defines a global function (a private method of Kernel) with the given name, implemented
by the C function func and taking argc arguments.
void
rb_define_singleton_method(VALUE classmod, char *name,
VALUE(*func)(), int argc")
Defines a singleton method in class classmod with the given name, implemented
by the C function func and taking argc arguments.
int
rb_scan_args(int argcount, VALUE *argv, char *fmt, ...")
Scans the argument list and assigns to variables similar to
scanf: fmt is a string containing zero, one, or two
digits followed by some flag characters.
The first digit indicates the count of
mandatory arguments; the second is the count of optional
arguments. A ``*'' means to pack the rest of the arguments into a
Ruby array. A ``&'' means that an attached code block will be
taken and assigned to the given variable (if no code block was
given, Qnil will be assigned).
After the fmt string, pointers to VALUE
are given (as with scanf) to which the arguments are
assigned.
Defines an alias for oldname in class or module
classmod.
Defining Variables and Constants
void
rb_define_const(VALUE classmod, char *name, VALUE value")
Defines a constant in the class or module classmod, with the
given name and value.
void
rb_define_global_const(char *name, VALUE value")
Defines a global constant with the
given name and value.
void
rb_define_variable(const char *name, VALUE *object")
Exports the address of the given object that was created
in C to the Ruby namespace as name. From Ruby, this will
be a global variable, so name should start with a leading
dollar sign. Be sure to honor Ruby's rules for allowed variable
names; illegally named variables will not be accessible from Ruby.
void
rb_define_class_variable(VALUE class, const char *name,
VALUE val")
Defines a class variable name
(which must be specified with a ``@@'' prefix) in the given
class, initialized to value.
Exports a virtual variable to Ruby namespace as the global
$name. No
actual storage exists for the variable; attempts to get and set
the value will call the given functions with the prototypes:
VALUE getter(ID id, VALUE *data,
struct global_entry *entry);
void setter(VALUE value, ID id, VALUE *data,
struct global_entry *entry);
You will likely not need to use the entry parameter
and can safely omit it from your function
declarations.
void
rb_define_hooked_variable(const char *name,
VALUE *variable, VALUE(*getter)(), void(*setter)()")
Defines functions to be called when reading or writing to
variable. See also rb_define_virtual_variable.
void
rb_define_readonly_variable(const char *name,
VALUE *value")
Same as rb_define_variable, but read-only from Ruby.
void
rb_define_attr(VALUE variable, const char *name,
int read, int write")
Creates accessor methods for the given variable, with the given
name. If read is nonzero, create a read method; if
write is nonzero, create a write method.
void
rb_global_variable(VALUE *obj")
Registers the given address with the garbage collector.
Calling Methods
VALUE
rb_funcall(VALUE recv, ID id, int argc, ...")
Invokes the method given by id in the object recv
with the given number of arguments argc and the arguments
themselves (possibly none).
VALUE
rb_funcall2(VALUE recv, ID id, int argc, VALUE *args")
Invokes the method given by id in the object recv
with the given number of arguments argc and the arguments
themselves given in the C array args.
VALUE
rb_funcall3(VALUE recv, ID id, int argc, VALUE *args")
Same as rb_funcall2, but will not call private methods.
VALUE
rb_apply(VALUE recv, ID name, int argc, VALUE args")
Invokes the method given by id in the object recv
with the given number of arguments argc and the arguments
themselves given in the Ruby Arrayargs.
ID
rb_intern(char *name")
Returns an ID for a given name. If the name does not
exist, a symbol table entry will be created for it.
char *
rb_id2name(ID id")
Returns a name for the given id.
VALUE
rb_call_super(int argc, VALUE *args")
Calls the current method in the superclass of the current object.
Exceptions
void
rb_raise(VALUE exception, const char *fmt, ...")
Raises an exception.
The given string fmt and remaining arguments
are interpreted as with printf.
void
rb_fatal(const char *fmt, ...")
Raises a Fatal exception, terminating the process. No
rescue blocks are called, but ensure blocks will be called.
The given string fmt and remaining arguments
are interpreted as with printf.
void
rb_bug(const char *fmt, ...")
Terminates the process immediately---no handlers of any sort will
be called.
The given string fmt and remaining arguments
are interpreted as with printf.
You should call this function only if a fatal bug
has been exposed. You don't write fatal bugs, do you?
void
rb_sys_fail(const char *msg")
Raises a platform-specific exception corresponding to the last
known system error, with the given msg.
VALUE
rb_rescue(VALUE (*body)(), VALUE args,
VALUE(*rescue)(), VALUE rargs")
Executes body with the given args. If a
StandardError exception is raised,
then execute rescue with the given rargs.
VALUE
rb_ensure(VALUE(*body)(), VALUE args,
VALUE(*ensure)(), VALUE eargs")
Executes body with the given args. Whether or not an
exception is raised, execute ensure with the given rargs
after body has completed.
VALUE
rb_protect(VALUE (*body)(), VALUE args,
int *result")
Executes body with the given
args and returns nonzero in result if any exception
was raised.
void
rb_notimplement(")
Raises a NotImpError exception to indicate that the enclosed
function is not implemented yet, or not available on this
platform.
void
rb_exit(int status")
Exits Ruby with the given status. Raises a SystemExit
exception and calls registered exit functions and
finalizers.
void
rb_warn(const char *fmt, ...")
Unconditionally issues a warning message to standard error.
The given string fmt and remaining arguments
are interpreted as with printf.
void
rb_warning(const char *fmt, ...")
Conditionally issues a warning message to standard error if Ruby
was invoked with the -w flag.
The given string fmt and remaining arguments
are interpreted as with printf.
Iterators
void
rb_iter_break(")
Breaks out of the enclosing iterator block.
VALUE
rb_each(VALUE obj")
Invokes the each method of the given obj.
VALUE
rb_yield(VALUE arg")
Transfers execution to the iterator block in the current context,
passing arg as an argument. Multiple values may be passed
in an array.
int
rb_block_given_p(")
Returns true if yield would execute a block in the current
context---that is, if a code block was passed to the current method
and is available to be called.
VALUE
rb_iterate(VALUE (*method)(), VALUE args,
VALUE (*block)(), VALUE arg2")
Invokes method with argument args and block
block. A yield from that method will invoke
block with the argument given to yield, and a second
argument arg2.
VALUE
rb_catch(const char *tag, VALUE (*proc)(), VALUE value")
Equivalent to Ruby catch.
void
rb_throw(const char *tag , VALUE value")
Equivalent to Ruby throw.
Accessing Variables
VALUE
rb_iv_get(VALUE obj, char *name")
Returns the instance variable name (which must be specified
with a ``@'' prefix) from the given obj.
VALUE
rb_ivar_get(VALUE obj, ID name")
Returns the instance variable name from the given obj.
VALUE
rb_iv_set(VALUE obj, char *name, VALUE value")
Sets the value of the instance variable name (which must be
specified with a ``@'' prefix) in the given obj to
value. Returns value.
VALUE
rb_ivar_set(VALUE obj, ID name, VALUE value")
Sets the value of the instance variable name
in the given obj to value. Returns
value.
VALUE
rb_gv_set(const char *name, VALUE value")
Sets the global variable name (the ``$'' prefix is
optional) to value. Returns value.
VALUE
rb_gv_get(const char *name")
Returns the global variable name (the ``$'' prefix is
optional).
void
rb_cvar_set(VALUE class, ID name, VALUE val")
Sets the class variable name in the given
class to value.
VALUE
rb_cvar_get(VALUE class, ID name")
Returns the class variable name
from the given class.
int
rb_cvar_defined(VALUE class, ID name")
Returns Qtrue if the given class variable
name has been defined for class; otherwise, returns
Qfalse.
void
rb_cv_set(VALUE class, const char *name, VALUE val")
Sets the class variable name
(which must be specified with a ``@@'' prefix) in the given
class to value.
VALUE
rb_cv_get(VALUE class, const char *name")
Returns the class variable name (which must be specified
with a ``@@'' prefix) from the given class.
Object Status
OBJ_TAINT(VALUE obj")
Marks the given obj as tainted.
int
OBJ_TAINTED(VALUE obj")
Returns nonzero if the given obj is tainted.
OBJ_FREEZE(VALUE obj")
Marks the given obj as frozen.
int
OBJ_FROZEN(VALUE obj")
Returns nonzero if the given obj is frozen.
Check_SafeStr(VALUE str")
Raises SecurityError if current safe level > 0 and str is
tainted, or a TypeError if str is not a T_STRING.
int
rb_safe_level(")
Returns the current safe level.
void
rb_secure(int level")
Raises SecurityError if level <= current safe level.
void
rb_set_safe_level(int newlevel")
Sets the current safe level to newlevel.
Commonly Used Methods
VALUE
rb_ary_new(")
Returns a new Array with default size.
VALUE
rb_ary_new2(long length")
Returns a new Array of the given length.
VALUE
rb_ary_new3(long length, ...")
Returns a new Array of the given length and populated
with the remaining arguments.
VALUE
rb_ary_new4(long length, VALUE *values")
Returns a new Array of the given length and populated
with the C array values.
void
rb_ary_store(VALUE self, long index, VALUE value")
Stores value at index in array self.
VALUE
rb_ary_push(VALUE self, VALUE value")
Pushes value onto the end of array self. Returns
value.
VALUE
rb_ary_pop(VALUE self")
Removes and returns the last element from the array self.
VALUE
rb_ary_shift(VALUE self")
Removes and returns the first element from the array self.
VALUE
rb_ary_unshift(VALUE self, VALUE value")
Pushes value onto the front of array self. Returns
value.
VALUE
rb_ary_entry(VALUE self, long index")
Returns array self's element at index.
int
rb_respond_to(VALUE self, ID method")
Returns nonzero if self responds to method.
VALUE
rb_thread_create(VALUE (*func)(), void *data")
Runs func in a new thread, passing data as an
argument.
VALUE
rb_hash_new(")
Returns a new, empty Hash.
VALUE
rb_hash_aref(VALUE self, VALUE key")
Returns the element corresponding to key in self.
VALUE
rb_hash_aset(VALUE self, VALUE key, VALUE value")
Sets the value for key to value in
self. Returns value.
VALUE
rb_obj_is_instance_of(VALUE obj, VALUE klass")
Returns Qtrue if obj is an instance of klass.
VALUE
rb_obj_is_kind_of(VALUE obj, VALUE klass")
Returns Qtrue if klass is the class of obj or
class is
one of the superclasses of the class of obj.
VALUE
rb_str_new(const char *src, long length")
Returns a new String initialized with length characters
from src.
VALUE
rb_str_new2(const char *src")
Returns a new String initialized with the null-terminated
C string src.
VALUE
rb_str_dup(VALUE str")
Returns a new String object duplicated from str.
VALUE
rb_str_cat(VALUE self, const char *src, long length")
Concatenates length characters from src onto
the Stringself. Returns self.
VALUE
rb_str_concat(VALUE self, VALUE other")
Concatenates other onto
the Stringself. Returns self.
VALUE
rb_str_split(VALUE self, const char *delim")
Returns an array of String objects created by splitting
self on delim.
