People always said that it's impossible due to the difference in back focus. While it's true in the general sense, but then if you limit your usage, it might work.
In the general sense, C mount lenses have a much smaller image circle, and thus, we should expect heavy vignetting even if it comes into focus. Therefore, we just shouldn't expect it to work well in general.
Since C mount lenses have much shorter back focus than regular DSLR lenses, that means C mount lenese have to be placed very close (too close!) to the DSLR sensor in order to reach focus at infinity. However, if you don't mind about it, you can always use it as a macro lens. To demonstrate this concept, for a regular DSLR lens to use as a macro lens, you need an extension tube. For a C mount lens, since you cannot put it close enough to the imaging sensor, that means you are forced to have something like an extension tube... by then, macro photography became the default setting.
Virtually all DSLR has a corresponding T-ring which is M42 threaded, and the C mount has a 1 inch thread, so if you can find such a step down ring, macro photography with C mount lenses should be possible.