metalwing,看过来,帮个忙

HANDLE OpenOneDevice (HDEVINFO HardwareDeviceInfo,
PSP_INTERFACE_DEVICE_DATA DeviceInfoData,char *devName)

{
PSP_INTERFACE_DEVICE_DETAIL_DATA functionClassDeviceData = NULL;
ULONG predictedLength = 0;
ULONG requiredLength = 0;
HANDLE hOut = INVALID_HANDLE_VALUE;
int my_error;

SetupDiGetInterfaceDeviceDetail (HardwareDeviceInfo,DeviceInfoData,NULL,0,&requiredLength,NULL);

predictedLength = requiredLength;// sizeof (SP_FNCLASS_DEVICE_DATA) + 512;

functionClassDeviceData = (PSP_INTERFACE_DEVICE_DETAIL_DATA)malloc (predictedLength);
functionClassDeviceData->cbSize = sizeof (SP_INTERFACE_DEVICE_DETAIL_DATA);

//
// Retrieve the information from Plug and Play.
//怎么老是这里出错,报1784
if (! SetupDiGetInterfaceDeviceDetail (
HardwareDeviceInfo,
DeviceInfoData,
functionClassDeviceData,
predictedLength,
&requiredLength,
NULL))
{
my_error = GetLastError();
return INVALID_HANDLE_VALUE;
}

strcpy( devName,functionClassDeviceData->DevicePath) ;

hOut = CreateFile (
functionClassDeviceData->DevicePath,
GENERIC_READ | GENERIC_WRITE,
FILE_SHARE_READ | FILE_SHARE_WRITE,
NULL,
OPEN_EXISTING,
0,
NULL);

if (INVALID_HANDLE_VALUE == hOut)
{
}

free(functionClassDeviceData);

return hOut;
}
我用bcb写的,怎么老是在第二次SetupDiGetInterfaceDeviceDetail 是出错啊?报1784,怎么回事啊?

不知道.是否SetupDiGetInterfaceDeviceDetail (HardwareDeviceInfo,DeviceInfoData,NULL,0,&requiredLength,NULL)返回类型的问题?