Improve the doc for cv::Mat::checkVector.

samples/cpp/tutorial_code/snippets/core_mat_checkVector.cpp

@@ -0,0 +1,42 @@
+/**
+ * @brief It demonstrates the usage of cv::Mat::checkVector.
+ */
+
+#include <opencv2/core.hpp>
+
+int main()
+{
+    //! [example-2d]
+    cv::Mat mat(20, 1, CV_32FC2);
+    int n = mat.checkVector(2);
+    CV_Assert(n == 20); // mat has 20 elements
+
+    mat.create(20, 2, CV_32FC1);
+    n = mat.checkVector(1);
+    CV_Assert(n == -1); // mat is neither a column nor a row vector
+
+    n = mat.checkVector(2);
+    CV_Assert(n == 20); // the 2 columns are considered as 1 element
+    //! [example-2d]
+
+    mat.create(1, 5, CV_32FC1);
+    n = mat.checkVector(1);
+    CV_Assert(n == 5); // mat has 5 elements
+
+    n = mat.checkVector(5);
+    CV_Assert(n == 1); // the 5 columns are considered as 1 element
+
+    //! [example-3d]
+    int dims[] = {1, 3, 5}; // 1 plane, every plane has 3 rows and 5 columns
+    mat.create(3, dims, CV_32FC1); // for 3-d mat, it MUST have only 1 channel
+    n = mat.checkVector(5); // the 5 columns are considered as 1 element
+    CV_Assert(n == 3);
+
+    int dims2[] = {3, 1, 5}; // 3 planes, every plane has 1 row and 5 columns
+    mat.create(3, dims2, CV_32FC1);
+    n = mat.checkVector(5); // the 5 columns are considered as 1 element
+    CV_Assert(n == 3);
+    //! [example-3d]
+
+    return 0;
+}