Passing a Class as a Pointer

[crispin]

Hi Everyone,

I was hoping one of you kind souls could help me with the following:

I have a class method which initializes audio libraries written in C, shown below... where it says (RIGHT HERE) I am trying to create a pointer to the class MiniHost, am I doing it right?

>>>>>

void MiniHost::setupAudio()
{
////Some unimportant stuff here, then:

Pa_OpenStream(
&stream,
NULL,
&outputParameters,// ignore all this stuff
kSampleRate,
kBlockSize,
NULL,
patestCallback,
this); /////////// <- RIGHT HERE

Pa_StartStream( stream );

}

>>>>>

Here is the second part, a static method from which I am trying to call the class listed above:

>>>>>>>>>
static int patestCallback( const void *inputBuffer, void *outputBuffer,
unsigned long framesPerBuffer,
const PaStreamCallbackTimeInfo* timeInfo,
PaStreamCallbackFlags statusFlags,
void *userData ) //I can't change this stuff, the libraries need it this way
{

userData->someFunction(); //dosen't work

return paContinue;
}

>>>>>>>>>

What I need to do in the above code, is to call MiniHost through the 'userData' parameter, into which I tried to pass a pointer to the class.
Assuming I passed the pointer correctly, how do I call the class?

Thanks a lot!
Crispin

[Ganon11]

static int patestCallback( const void *inputBuffer, void *outputBuffer,
                            unsigned long framesPerBuffer,
                            const PaStreamCallbackTimeInfo* timeInfo,
                            PaStreamCallbackFlags statusFlags,
                            void *userData ) //I can't change this stuff, the libraries need it this way
{
 
   userData->someFunction(); //dosen't work
 
return paContinue;
}

What I need to do in the above code, is to call MiniHost through the 'userData' parameter, into which I tried to pass a pointer to the class.
Assuming I passed the pointer correctly, how do I call the class?

Thanks a lot!
Crispin

I'm not sure the header syntax is correct - userData is defined as a void*, or a pointer to nothing. Maybe you can cast userData to a MiniHost*, and then try ->someFunction(), as in:

static int patestCallback( const void *inputBuffer, void *outputBuffer,
                            unsigned long framesPerBuffer,
                            const PaStreamCallbackTimeInfo* timeInfo,
                            PaStreamCallbackFlags statusFlags,
                            void *userData ) //I can't change this stuff, the libraries need it this way
{
   userData = (MiniHost*)userData;
   userData->someFunction(); //dosen't work
 
return paContinue;
}

[willakawill]

Hi. A void pointer needs to be recast

((MiniHost*)userData)->someFunction(); //should work

[crispin]

Hi,

Thanks for your help... I got it working!

I passed the class as 'this'. And added 'MiniHost *m = (MiniHost*)userData;' in the static int. To use the methods I simply type m->whatever();

Cheers,
Crispin

[willakawill]

Hi,

Thanks for your help... I got it working!

I passed the class as 'this'. And added 'MiniHost *m = (MiniHost*)userData;' in the static int. To use the methods I simply type m->whatever();

Cheers,
Crispin

Be careful. At this point you have 2 pointers pointing to the same class. An unnecessary risk