libusb_get_device_list seg fault - c++

Question

I am writing a file explorer application in Qt C++ and have a libUSB function (QList UsbDevice::getDeviceList()) which gets all attached USB devices, checks each one for my products vendor and product ID's, claims them and the returns them in an array. This all works fine and I get the device I want, however I have added a refresh button which should update the device list shown in a drop-down list (it basically calls the getDeviceList function again) but it seg faults when calling:
int numDevices = libusb_get_device_list(NULL, &usbDevices);
the second time around and I can't for the life of me see why. If someone could check over the code below and see if I have missed something stupid that would be very helpful.
QList<UsbDevice*> UsbDevice::getDeviceList()
{
unsigned char manf[256] = {'\0'};
QList<UsbDevice*> usbDeviceList;
libusb_device **usbDevices;
struct libusb_device_descriptor desc;
int numDevices = libusb_get_device_list(NULL, &usbDevices);
if(numDevices < 0)
{
libusb_free_device_list(usbDevices, 1);
return usbDeviceList;
}
QString error;
for(int i=0; i!=numDevices; ++i)
{
libusb_device *dev = usbDevices[i];
libusb_get_device_descriptor(dev, &desc);
if((desc.idVendor != VendorUsbId) && (desc.idProduct != ProductUsbId))
continue;
libusb_device_handle *handle = NULL;
libusb_config_descriptor *conf_desc = NULL;
int result = 0;
result = libusb_open(dev, &handle);
if(result < 0)
{
if(result == -3)
{
}
error = QString(libusb_error_name(result));
continue;
}
int config = 1;
if( handle == NULL)
{
continue;
}
result = libusb_set_configuration(handle, config);
if(result < 0)
{
error = QString(libusb_error_name(result));
continue;
}
result = libusb_get_config_descriptor(dev, 0, &conf_desc);
if(result < 0)
{
error = QString(libusb_error_name(result));
continue;
}
result = libusb_claim_interface(handle, 0);
if(result < 0)
{
error = QString(libusb_error_name(result));
continue;
}
result = libusb_get_string_descriptor_ascii(handle, desc.iProduct, manf, sizeof(manf));
if(result < 0)
{
error = QString(libusb_error_name(result));
continue;
}
UsbDevice *newDevice = new UsbDevice();
newDevice->setDeviceName(QString((char*)manf));
newDevice->setHandle(handle);
usbDeviceList << newDevice;
}
libusb_free_device_list(usbDevices, 1);
return usbDeviceList;
}

Answer 1

You are calling libusb_init() at the beginning of your program, but you are also calling libusb_exit() at the beginning : before calling a.exec().
Your first call probably happens in MainWindow constructor ?
You could instead subclass QApplication, call libusb_init() in the constructor and libusb_exit() in the destructor.