Interpreting inputBuffer's Value in a Callback - callback

Question

I am basing my code off of Portaudio's paex_record_file.c example. One of the parameters in the callback is inputBuffer, and I wanted to use its data to calculate other numbers with the double/float type. I changed the file from a .raw to a .txt, but notepad still cannot read it, leading me to believe its data is not actually encoded as a number. How is the data stored in inputBuffer and how can I do arithmetic with it (add, multiply, divide, etc)?
This is how I initialized inputParameters:
inputParameters.device = Pa_GetDefaultInputDevice(); /* default input device */
if (inputParameters.device == paNoDevice) {
fprintf(stderr,"Error: No default input device.\n");
goto error;
}
inputParameters.channelCount = 2; /* stereo input */
inputParameters.sampleFormat = paFloat32;
inputParameters.suggestedLatency = Pa_GetDeviceInfo( inputParameters.device )->defaultLowInputLatency;
inputParameters.hostApiSpecificStreamInfo = NULL;
This question is somewhat related to print floats from audio input callback function (unanswered).

Answer 1

The inputBuffer parameter to the callback is a void*. The actual type of the underlying buffer depends on the parameters and the flags that you pass to Pa_OpenStream.
If you specified paFloat32 then there will be a float* in there somewhere. However the are two possibilities:
Interleaved: inputParameters.sampleFormat = paFloat32;
Non-Interleaved: inputParameters.sampleFormat = paFloat32|paNonInterleaved;
You specified the interleaved option. In this case, inputBuffer points to a single buffer of interleaved floats. So you can write:
float *samples = (float*)inputBuffer;
In a two channel stream samples will contain interleaved left and right samples, e.g.:
samples[0]; // first left sample
samples[1]; // first right sample
samples[2]; // second left sample
samples[3]; // second right sample
// etc.
For completeness: If it had been a non-interleaved stream then inputBuffer points to an array of pointers to single-channel buffers. To extract the buffer pointers you would write something like:
float *left = ((float **) inputBuffer)[0];
float *right = ((float **) inputBuffer)[1];
Note that in all cases framesPerBuffer counts frames not samples. A frame includes one sample from each channel. For example, in a stereo stream, a frame includes both the left and right channel samples.