[cffi-devel] Dynamically call a certain function in a lib

[Anton Kovalenko]

Frank Goenninger <frgo at me.com> writes:

> The marked line should load the "open" function in the just loaded
> foreign lib. As I intend to load multiple so-called modules where each
> module has an "open" function I /think/ I need to say which open()
> function to call (the loaded libs are C DLLs, mostly).
>
> How do I name a certain foreign lib in the call to foreign-funcall
> when the library given is not evaluated ?

Many CFFI backends have CFFI-FEATURES:FLAT-NAMESPACE, which you can (or
can't) see in *features*. If you see it present after loading CFFI in
your CL implementation, it means that underlying /native/ FFI is unable
to work with multiple functions having the same name in different
modules. If there is no CFFI-FEATURES:FLAT-NAMESPACE in *FEATURES*, you
can use something like (CFFI:FOREIGN-FUNCALL ("open" :library
my-module)), but it's fantastically unportable, and you'll have to
DEFINE-FOREIGN-LIBRARY for each module in use.

Fortunately, CFFI:FOREIGN-FUNCALL-POINTER is widely available, so you
may solve it the following way:

* define foreign interface to dlopen [or LoadLibrary] and dlsym [or
  GetProcAddress]

* load your module by calling dlopen [or LoadLibrary]

* call dlsym(<your-module-handle>,"open") [or GetProcAddress]

* dlsym/GetProcAddress returns a pointer to function, which you may call
  with CFFI:FOREIGN-FUNCALL-POINTER.

-- 
Regards, Anton Kovalenko <http://github.com/akovalenko/sbcl-win32-threads/wiki>
+7(916)345-34-02 | Elektrostal' MO, Russia