Jarvis algorithm (check colinear points)

how to check co linear points in jarvis algorithm ?

As jarvis algorithm explains us the idea that

  orientation(p,r,q) == 2 than take  r and skip q

but if orientation(p,r,q) == 0 and r is farther than q , at that time we have to take r and skip q but there is no implementation for it.

how we check it