libusb failing at getting string descriptor on some devices - c++

Question

I am trying to get information about all attached devices.
This is my code:
libusb_device_descriptor desc;
libusb_config_descriptor *conDesc;
char szBuffer[256] = { 0 };
unsigned char strDesc[256];
libusb_device_handle *devHandle = NULL;
int retVal = 0;
__int64 i64Temp;
DWORD dwProdId;
DWORD dwProdId1;
i64Temp = 13888;
dwProdId = (DWORD)i64Temp;
retVal = libusb_open(dev, &devHandle);
int r = libusb_get_device_descriptor(dev, &desc);
if (r < 0)
{
cout << "failed to get device descriptor" << endl;
return;
}
r = libusb_get_config_descriptor(dev, 0, &conDesc);
printf("Interface Class = %d\n", conDesc->interface->altsetting->bInterfaceClass);
cout << "Number of possible configurations: " << (int)desc.bNumConfigurations << "" << endl;
cout << "Device Class: " << desc.bDeviceClass << endl;
cout << "Device Class: " << desc.bDeviceSubClass << endl;
printf("Class = %d\n", desc.bDeviceClass);
cout << "VendorID: " << desc.idVendor << endl;
cout << "ProductID: " << desc.idProduct << endl;
if (retVal == LIBUSB_SUCCESS)
{
retVal = libusb_get_string_descriptor_ascii(devHandle, desc.iManufacturer, strDesc, 256);
printf("Manufacturer: %s\n", strDesc);
retVal = libusb_get_string_descriptor_ascii(devHandle, desc.iSerialNumber, strDesc, 256);
printf("SerialNumber: %s\n", strDesc);
retVal = libusb_get_string_descriptor_ascii(devHandle, desc.iProduct, strDesc, 256);
printf("Product: %s\n", strDesc);
printf("\n\n");
}
else if (retVal != LIBUSB_SUCCESS)
{
printf("retVal failed");
printf("\n\n");
}
My code knows that there are 8 devices connected but it's getting manufacturer or serial number only on two of them. I would like to get this information for all of the attached devices.