Yes, You can. The entire Linux device interface, to name just one example, if full of interfaces. The way to accomplish this is via pointer to functions, and to have it as an object, have these pointer to functions grouped in a struct.
GTK/Glib is notably full of these interfaces too.
Yup. In a past job I did a lot of work writing ALSA drivers for custom souncards. The ALSA interface is a good example of this. They provide an API app developers can use to do sound stuff (change the volume, for example). In your sound card driver you provide an implementation of the API to do whatever changing the volume means for your particular hardware (in my case sending an i2c message to a digital potentiometer).
