Hi,
You are right, the implementation of the InteractionContext class (which extends an empty struct) is only accessible on the server side (i.e. inside the EyeX Engine). As a client application, you should not need to care about creating new instances of this, just call txCreateContext, keep track of the pointer and make sure to release it when shutting down. Please check out one of the C samples, for example MinimalGazeDataStream.c