I usually do not require students to attend the lectures, nor do I keep a record of who attends. Nevertheless, the course consists of what is covered in the lectures and assignments, so all students are responsible for knowing what was covered in the lectures and assignments.
The textbook (if one is assigned) is a reference for the course, but the book is not the course itself. I may discuss material not found in the book, and if I do then that material becomes part of the course.
If you miss a lecture, please learn from a classmate what was covered.