OpenCV row (high) and column (wide) parameter order problem _OPENCV

I've met a couple of times before. Due to a row and column error causing the pointer to go out of bounds, here are some of the things I've summarized:

Condition one (definition iplimage*):

IPLIMAGE*DST = NULL;
DST =cvcreateimage (cvsize), ipl_depth_8u, 3);

The DST created here is 480 rows and 600 columns, preceded by a row.

Situation two (definition mat):

Mat DST;
DST =mat (CV_8UC3);

The DST created here is also 480 rows and 600 columns, but the first column.

Situation three (defining areas of interest):

Rectroi_rect;
roi_rect.x=10;
roi_rect.y=20;

This represents the coordinate (x,y) of the upper-left pixel of the defined area of interest (rectangle) (10,20), which is in row 20th, column 10th.

These details are important, and when you traverse a picture using nested for loops, there is a good chance that if you don't pay attention to the details of the rows and columns, there is a high likelihood of errors in the pointer crossing.

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2016.11.03 Supplements

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Yesterday, the lab students found the following situation:

Use

Mat img = Mat (cv::size (), CV_8UC3);

The img defined is 600 rows, 480 columns.

And the situation I mentioned above two is defined by 480 lines, 600 columns ... Note the use of cv::size.

Special attention should be paid here.