#includeEigen::MatrixXd matrix(3, 4); int num_cols = matrix.cols();
#includearma::mat matrix(3, 4); int num_cols = matrix.n_cols;
#includeIn all of these examples, we create a matrix of size 3x4 and then determine the number of columns in the matrix using the appropriate function or attribute. The package/library used in each example is Eigen, Armadillo, and OpenCV, respectively.cv::Mat matrix(3, 4, CV_64F); int num_cols = matrix.cols;