I have a problem in writing a wrapper for Port audio dll in LabVIEW. The sequence is query the sound devices and find the one which supports ASIO and has outputs and then start a stream using PortAudio DLL. The function prototypes in the header file are as follows: typedef void PaStream; int Pa_Initialize( void ); int Pa_OpenStream( PaStream** stream); int Pa_StartStream( PaStream *stream ); int Pa_StopStream( PaStream *stream ); There is a C example using the following sequence: err = Pa_Initialize(); err = Pa_OpenStream(&stream) err = Pa_StartStream( stream ); err = Pa_StopStream( stream ); Now to use this in LabVIEW, I read the following threads: https://forums.ni.com/t5/LabVIEW/Creating-a-pointer-to-void-to-pointer/td-p/3582162 https://forums.ni.com/t5/LabVIEW/Passing-a-Void-pointer-to-a-DLL-in-Labview/td-p/2756716 and based on that I created the attached example_sine.vi, which uses LabVIEW:DSNewPtr to generate a pointer and pass its value and pointer to the functions, but it is giving the error: Invalid stream pointer. Any help will be highly appreciated.

@Mahyara a écrit : I created the attached example_sine.vi, which uses LabVIEW:DSNewPtr to generate a pointer and pass its value and pointer to the functions, but it is giving the error: Invalid stream pointer. Any help will be highly appreciated. You don't need to deal with DSNewPtr at all. Your stream is just 64 bit address (allocated by library), so you need to pass just U64 "holder": That is. You have couple of other troubles (with callback where address passed instead of value). Minimal but functional example (very quick and dirty) example, based on c code, which plays sine wave on default audio device: in the attachment downgraded to LV2018.

LabVIEW

Problem with a DLL Pointer and Pointer to Pointer in LabVIEW

Solved!

@rolfk wrote:
As to callback functions in a DLL from LabVIEW VIs, that is a concept that I pondered a few times but considered it simply not practical. I consider the solution more brittle than a spider rag, a total maintenance nightmare and pretty much nothing I would ever want to support for average LabVIEW users. They don't understand the difficulties and will mess up over and over again. If you can't write C code to implement the callback functions yourself (one of the more advanced C programming topics) you can't really comprehend the difficulties not even for just using an existing solution. But if you know how to write the according C code, its simply a ten fold simpler to do it that way than trying to do callback functions in LabVIEW.

I can write a callback function in LabVIEW, by compiling to a dll, that's no problem.

I prefer a LV dll (over C), because the LV dll function can easily call a VI by reference, and this VI can easily communicate with the 'user space' (dev.env or exe). DVR references stopped working this way in LV24 though...

The only problem is the callback VI needs two inputs for each pointer input\output. You can't use a 64 bit integer as a pointer input\output for a 32 bit dll... And vice versa.