c++ - Open CV convexity defects drawing -

i trying join convexity defects in opencv of line. convexity defects stored in defects using vector> how access elements of particular defect(4 element integer array) suppose drawing liness using

for (int = 0; < defects.size(); i++){             line(frame,\\startindex;\\endindex,color,thickness,linetype);         } 

how start index , end index paricular defect? have gone through similar questions cant seem understand