[LAD] ladspa c++ dlsym question

james jwm-art net james at jwm-art.net
Wed Nov 21 16:17:27 UTC 2007

Thankyou, that does the trick.

You can expect to see a new release of "Wav Composer Not Toilet"

It will include selected LADSPA plugins - hardcoded - so plugins not
supported will not be available.

and mandatory dependancy on libsndfile for all wav reading/writing.

Which should hopefully make it a whole lot nicer.

Dunno why I've been so scared of doing this, it's not so complex after
all :)


On 21/11/2007, "Lars Luthman"  wrote:

>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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