Problems with vector <DMatch>

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I am trying to implement code from here: http://docs.opencv.org/doc/tutorials/features2d/feature_flann_matcher/feature_flann_matcher.html#feature-flann-matcher

into an Android app. I've added nonfree modules which I complied according to this tutorial: http://web.guohuiwang.com/technical-notes/sift_surf_opencv_android

but I'm getting errors in:

for( int i = 0; i < descriptors_object.rows; i++ ) { if( matches[i].distance < 3*min_dist ) { good_matches.push_back( matches[i]); } }

Field 'distance' could not be resolved Invalid arguments ' // for push_back

Any ideas how to fix it?