Making a VALUE visible to multiple source files

[Daniel Berger]

Hi,

I'm having some trouble pre-declaring some VALUE's. I've got a VALUE
cFoo I want to be visible to multiple source files. Say the layout is
something like this:

foo/ext/stuff/extconf.rb
foo/ext/stuff/foo.c
foo/ext/stuff/bar.c
foo/ext/stuff/baz.h
foo/ext/stuff/stuff.c

I want to define all the class VALUE's in the header file. I would
then like to be able to '#include "baz.h"' inside both foo.c and
bar.c. However, that causes an ld error when I try to build the source
files:

ld: duplicate symbol _cFoo in foo.o and bar.o

# extconf.rb
require 'mkmf'
create_makefile('stuff')

# Rakefile
require 'rake'
require 'rake/extensiontask'
Rake::ExtensionTask.new('stuff')

// baz.h
#ifndef BAZ_H_INCLUDED
#define BAZ_H_INCLUDED
#include <ruby.h>
VALUE cFoo;
VALUE cBar;
#endif

Why do I want to do this? In the long run, I'm trying to figure out
how to setup Check_Type calls for my own classes, e.g.
Check_Type(some_value, cFoo);

Regards,

Dan

 

[Joel VanderWerf]

I want to define all the class VALUE's in the header file. I would
then like to be able to '#include "baz.h"' inside both foo.c and
bar.c. However, that causes an ld error when I try to build the source
files:

Try "extern VALUE ..." in the headers, and "VALUE ..." in one source file.

 

[Daniel Berger]

This is a pretty standard C technique:

in baz.h:

#ifndef BAZ_H_INCLUDED
#define BAZ_H_INCLUDED
#include <ruby.h>
//these lines just say that these variables exist
extern VALUE cFoo;
extern VALUE cBar;
#endif

in *one* of your .c files (presumably baz.c)

//these lines declare memory for these variables
//and need to appear exactly once in your project
VALUE cFoo;
VALUE cBar;

Ken, Joel,

Thanks. I don't know why, but I had it in my head that I didn't have
to extern the values.

Regards,

Dan