[LAD] ladspa c++ dlsym question

Lars Luthman lars.luthman at gmail.com
Wed Nov 21 11:00:23 UTC 2007

On Wed, 2007-11-21 at 02:57 +0000, james jwm-art net wrote:
> Hi,
> I'm attempting to use dlsym to dynamically load a ladspa plugin lib in
> c++. I've found various web pages describing how to use dlsym in c++
> but they do not seem entirely relevant to using ladspa (ie ladspa
> plugins are mainly written in c) (??).

The LADSPA interface is defined in terms of C structures and types, so
the language used to write the plugin doesn't matter to the loader.
dlsym() is what you use. Strictly speaking it should not work in a
standards-compliant compiler without some ugly tricks since casting void
pointers (which is what dlsym() returns) to function pointers is not
allowed in C++, but fortunatly most compilers are not that strict about

If you really want your code to work in a strict compiler you can do
something like

union {
 void* in;
 LADSPA_Descriptor_Function out;
} foo;
foo.in = dlsym(lib_handle, "ladspa_descriptor");
LADSPA_Descriptor* descriptor = (*foo.out)(0);

which will not generate any errors, but _will_ invoke undefined
behaviour. It works on all platforms I've tried though.

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