# Static functions, extensions, linkage

**URL:** <https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947>\
**Category:** Ruby\
**Created:** [August 2, 2006, 2:10am UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947 "2006-08-02T02:10:54Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 2, 2006, 2:10am UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/1 "2006-08-02T02:10:54Z")

</div>

Hi,

How do you get at a static function from within a C extension? I tried  
this snippet where I attempt to use flo\_plus from numeric.c:

/\* foo.c \*/  
#include \<ruby.h\>

extern VALUE flo\_plus(VALUE, VALUE);

static VALUE foo\_test(VALUE x, VALUE y){  
return flo\_plus(x, y);  
}

void Init\_foo(){  
VALUE cFoo = rb\_define\_class(“Foo”, rb\_cObject);  
rb\_define\_method(cFoo, “test”, foo\_test, 2);  
}

# test.rb

$:unshift Dir.pwd  
require ‘foo’  
f = Foo.new  
f.test

This result is:

ruby: symbol lookup error:  
/home/djberge/programming/ruby/extensions/foo.so: undefined symbol:  
flo\_plus

I tried linking explicitly against -lruby but that didn’t help.

Regards,

Dan

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 2, 2006, 2:29am UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/2 "2006-08-02T02:29:24Z")

</div>

Daniel B. wrote:

> static VALUE foo\_test(VALUE x, VALUE y){  
> require ‘foo’
> 
> Regards,
> 
> Dan

Where is ‘flo\_plus’ defined?

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 2, 2006, 2:58am UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/3 "2006-08-02T02:58:08Z")

</div>

Timothy H. wrote:

> > $:unshift Dir.pwd  
> > I tried linking explicitly against -lruby but that didn’t help.
> > 
> > Regards,
> > 
> > Dan
> 
> Where is ‘flo\_plus’ defined?

In numeric.c. Note that it _builds_ fine, it just doesn’t _run_.

Regards,

Dan

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 2, 2006, 3:08am UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/4 "2006-08-02T03:08:16Z")

</div>

Daniel B. wrote:

> > > #include \<ruby.h\>  
> > > }  
> > > /home/djberge/programming/ruby/extensions/foo.so: undefined symbol:

I see. Since flo\_plus has static linkage in numeric.c you can’t call it  
from your extension. It builds okay because you supplied a declaration  
for it, and it links okay because Linux does lazy linking (that is,  
external symbols aren’t resolved until the .so gets loaded), but it  
won’t run because there’s no external definition of flo\_plus to match  
your external reference.

You’ll have to use rb\_funcall to call “+”.

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 3, 2006, 12:03pm UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/5 "2006-08-03T12:03:20Z")

</div>

Hello !

> This result is:
> 
> ruby: symbol lookup error:  
> /home/djberge/programming/ruby/extensions/foo.so: undefined symbol:  
> flo\_plus
> 
> I tried linking explicitly against -lruby but that didn’t help.

By the way, if you’re interested to know which symbols are exported  
from a library, just do

nm -D /usr/lib/library.so

A look to that on my computer shows no references to flo\_plus, only:  
nm -D /usr/lib/libruby1.8.so | grep flo  
U flock  
U floor  
0000000000057ef0 T rb\_float\_new

Cheers

```
Vincent
```

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 3, 2006, 12:02pm UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/6 "2006-08-03T12:02:00Z")

</div>

On Aug 1, 2006, at 8:10 PM, Daniel B. wrote:

> Hi,
> 
> How do you get at a static function from within a C extension? I  
> tried  
> this snippet where I attempt to use flo\_plus from numeric.c:

I could be wrong, but I believe the entire purpose of a static  
function is to _not_ be get at able from other code (sort of like  
private in ruby).

---

<div class="post-metadata">

**Author:** ![danielb](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/c57346/32.png) [@danielb](https://www.ruby-forum.com/u/danielb)\
**Post date:** [August 3, 2006, 12:32pm UTC](https://www.ruby-forum.com/t/static-functions-extensions-linkage/100947/7 "2006-08-03T12:32:06Z")

</div>

Vincent F. wrote:

> 0000000000057ef0 T rb\_float\_new  
> In Ruby, the functions that are intended for use by extensions start  
> with the prefix “rb\_” and are declared in either ruby.h or intern.h.  
> Since flo\_plus doesn’t start with “rb\_” it isn’t intended to be  
> available to extensions.