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first, please do not use CvMat, IplImage or anything from the deprecated opencv1.0 c-api. please stick with cv::Mat and c++.

then, neither example probably does , what you want. before you can set values of a Mat, you have to allocate memory, like:

Mat m(3,3,CV_8U);
m.setTo(Scalar::all(17));

or, all in one go:

Mat m(3,3,CV_8U,Scalar::all(17));

(and again, you should ignore the 1st example entirely, it is no more valid today)

please also have a look at the tutorials