Error : unknown type name 'FeatureTracks'

I had made an structure for feature tracks:

struct FeatureTracks{
    std::vector<std::vector<cv::Point2f> > tracks;
    std::vector<size_t> offset;
};

Then making a function to call it:

void genTrackMatrix(const std::vector<cv::Mat>& images, FeatureTracks& trackMatrix, int tWindow,  int stride);

But the function calling is giving an error:unknown type name 'FeatureTracks'

Please help me out. Thanks in advance.