When installing opencv 3.0 and opencv_contrib, i just follow the tutorial using linux command and get the source code from github. Both are installed successfully, but when i write:
include "opencv2/xfeatures2d"
It turns out opencv can not find the file. When I refer to the path usr/local/include/, I can not find this file myself too. Since everything complied successfully, I dont know what is wrong with this file.