using haarcascade in bbb

ive installed opencv in bbb and found the location of haarcascade dace detector at
how do i specify the path to get access the classifier
i tried root:/usr/share/haarcascades/<> and got error
what additional detail should i add while using haarcascades

May be this will help

the face detection part is not working using haar classfier even with the code provided in the link
anything to configure or any prerequisites for using haar cascade method?