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From: Daniel Berger on 25 Feb 2010 12:38
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

From: Joel VanderWerf on 25 Feb 2010 14:17
Daniel Berger wrote:
> 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.

From: Daniel Berger on 25 Feb 2010 16:15


On Feb 25, 1:08 pm, Ken Bloom <kbl...(a)gmail.com> wrote:
> Daniel Berger <djber...(a)gmail.com> wrote:
> > 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
>
> 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

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