using cout with Mat object

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I have met the same problem, I am using opencv 2.4.6.0 and visual studio professional 2012 The only solution I found for my code is if you have an CV_32FC1 type use warp_mat = Mat::zeros(2, 3, CV_32FC1);

    cout << "Warp_mat = " <<endl;
    for ( int i = 0; i <3; i++)
    {
        cout<<" " << warp_mat.at<float>(0, i) ;
    }
    cout << " " <<endl;
    for ( int i = 0; i <3; i++)
    {
            cout<<" " << warp_mat.at<float>(1, i) ;
    }
    cout << " " <<endl;

That was at the initialization stage, later after getting the affine the function changed it to a cv_64F therefore you cannot use that code but instead you have to use the following

    cout << "Warp_mat = " <<endl;
    for ( int i = 0; i <3; i++)
    {
            cout<<" " << warp_mat.at<double>(0, i) ;
    }
    cout << " " <<endl;
    for ( int i = 0; i <3; i++)
    {
        cout<<" " << warp_mat.at<double>(1, i) ;
    }
    cout << " " <<endl;

You are trying to print a pointer to mat instead of the mat. Replace the cout line with

cout << "O = " << endl << " " << O.at<float>(0,0) << endl << endl;

and it works. Notice the use of at<float>.

There is C++ I/O Mat example cout_mat.cpp. You can use it as reference.

just to add: I print every 3 seconds one line of my cv::Mat encoded as 16UC1 as my video-feed has @30fps

    int count; cv::Mat dImg;
    if(count == 90){
        for(int i = 0; i<dImg.cols;i++){
            cout<<" "<<unsigned(dImg.at<uchar>(240,i));
        }
        count = 0; 
    }   
    count++;