Referred by an employee, I got the interview after a remote programming test. It took about nearly 3 hours from the very beginning to end. It was a complete technical interview, with no discussion of anything else. Three engineers interviewed me. Mainly, two of them asked questions from data structures, C, C++, and Linux. They asked questions from simple to hard and gradually detailed into the code implementation. You not only had to answer the question, but you also needed to explain why you thought your answer was right. They wouldn't change to another question unless you could explain the answer totally clearly, or you were just stuck and couldn't say anything more.

Quite a lot: data types in C, linked lists, class members, I cannot remember all of them. How to find and identify memory leaks, and how to get out of bugs in code when the program/device is already online and you cannot stop it to debug.