typedef int XPLMPluginID;
Each plug-in is identified by a unique integer ID. This ID can be used to disable or enable a plug-in, or discover what plug-in is 'running' at the time. A plug-in ID is unique within the currently running instance of X-Plane unless plug-ins are reloaded. Plug-ins may receive a different unique ID each time they are loaded.
For persistent identification of plug-ins, use XPLMFindPluginBySignature in XPLMUtiltiies.h
-1 indicates no plug-in.