Checking for Lost Keyboard Input

Because Windows may force your application to unacquire the keyboard when you have set the cooperative level to DISCL_FOREGROUND and the focus switches to another application, you should check for the DIERR_INPUTLOST return value from the IDirectInputDevice::GetDeviceData or IDirectInputDevice::GetDeviceState methods, and attempt to reacquire the keyboard if necessary. (See Acquiring Devices.)

Note You should not attempt to reacquire the keyboard on getting a DIERR_NOTACQUIRED error. If you do, you are likely to get caught in an infinite loop: acquisition will fail, you will get another DIERR_NOTACQUIRED error, and so on.