According to the document, it says: If successful, returns a (non-negative) device descriptor. On failure, -1 is returned.
I follow the sample code to check if the instruments such as agilent 34401A connect with GPIB connector is succeed, when I remove the agilent 34401A from GPIB connector and use ibdev command to verify if it's removed succeed, the return value isn't return -1, it is display 31256 (see attachment).
I can't understand why..I need some help, how to check the instrument is removed from the GPIB connector?
I'm having the same problem. In this case I have 2 instruments communicating through GPIB and the ibdev comand (even when the cable is not connected) returns 31256 and 31257. I have no idea how to solve this problem, help me please.