Wrong error code - c++

Question

I'm using portaudio to play a sound. I want to be able to select the output via the UI. I managed it like that :
PaError err = Pa_Initialize();
if( err != paNoError )
return false;
qDebug() <<"Port audio succeed initialization !";
int numDevices;
numDevices = Pa_GetDeviceCount();
if( numDevices <= 0 )
{
qDebug() << "ERROR: Pa_CountDevices returned " << numDevices;
return false;
}
const PaDeviceInfo *deviceInfo;
bool isThereOutput = false;
int i = 0;
while(i < numDevices and !isThereOutput)
{
deviceInfo = Pa_GetDeviceInfo( i );
isThereOutput = (deviceInfo->maxOutputChannels > 0);
i++;
}
if(!isThereOutput)
{
qDebug() << "No output device";
return false;
}
PaError errorOpening;
if(outputDevice != "")
{
PaStreamParameters outputDeviceInfo;
int numDevices = Pa_GetDeviceCount();
const PaDeviceInfo *deviceInfo;
for(int i = 0; i<numDevices; i++ )
{
deviceInfo = Pa_GetDeviceInfo( i );
if(deviceInfo->maxOutputChannels > 0 && deviceInfo->name == outputDevice)
{
outputDeviceInfo.device = i;
outputDeviceInfo.channelCount = 1;
outputDeviceInfo.sampleFormat = paInt8;
outputDeviceInfo.suggestedLatency = deviceInfo->defaultLowOutputLatency;
}
}
if(outputDeviceInfo.channelCount > 1)
{
errorOpening = Pa_OpenStream(&stream, NULL, &outputDeviceInfo, SAMPLE_RATE, FRAME_PER_BUFFER, paNoFlag, audioCallback, this);
}
}
if(outputDevice == "" or errorOpening != paNoError)
{
if(errorOpening != paNoError)
qDebug() << "Can't open selected device ("<< outputDevice <<"), switching to the default one. Error : " << Pa_GetErrorText(errorOpening);
errorOpening = Pa_OpenDefaultStream( &stream,
0, /* no input channels */
1, /* mono output */
paInt8, /* 8 bits output */
SAMPLE_RATE,
FRAME_PER_BUFFER, /* frames per buffer, i.e. the number
of sample frames that PortAudio will
request from the callback. Many apps
may want to use
paFramesPerBufferUnspecified, which
tells PortAudio to pick the best,
possibly changing, buffer size.*/
audioCallback, /* this is your callback function */
this ); /*This is a pointer that will be passed to
your callback*/
}
if(errorOpening != paNoError)
return false;
if(Pa_StartStream( stream ) != paNoError)
return false;
And it fails :
Can't open selected device ( "Sortie intégr" ), switching to the default one. Error : Invalid error code (value greater than zero)
But I can't figure why OpenStream fails with a strange error code and Pa_OpenDefaultStream works like a charm.
So :
Why does it fails ?
Why does it throw a wrong error code ?

Answer 1

I assume you use C++ (though there are several curious and and or in your code.)
If your for loop didn't find any PaDeviceInfo which satisfies eviceInfo->maxOutputChannels > 0 && deviceInfo->name == outputDevice, then your outputDeviceInfo is left un-initialized. That means its channelConnect can have any values including large negative values. Then Pa_OpenStream isn't invoked and your errorOpening is also left un-initialized. I bet that's the reason of Invalid error code (value greater than zero) when you feed it into Pa_GetErrorText().