A variable saved in a structure as a mat file in 2018b seems unreadable in 2020b

Hi,

I am trying to switch to 2020b due to the cloud feature in this new version. A variable was saved in a structure, saved as the mat file named configV2.mat in 2018b. I was able to access or read the values of the variables named config.defects{1,1} as the following:

>> config.defects{1,1}

ans =

1×89 Defect array with properties:

xPositionStart

xPositionEnd

channelStart

channelEnd

isReported

defectReport

defectContour

However, when I was trying to load the SAME configV2.mat file in 2020b in the command line, it says empty value.

>> config.defects{1,1}

ans =

[]

Has anyone encountered this so far? Hope can get some suggestions on why this is happening here. Looks like I won't be able to upgrade to 2020b unless the structure needs to be resaved in a compatible format in 2018b, which is not an option for me at this moment. Looking forward to any clues on this issue. Appreciated! Joann

Answer 1

[Steven Lord]

If the definition of the Defect class is not available when you try to load it from the mat-file how would MATLAB know how to construct such an object? It's like you're asking MATLAB to read a book written in Klingon but it doesn't know that language.

I suspect that when you tried to load the file in the newer release you received a warning message, didn't you? If you did, what did that warning message say?

[Zhao Ren]

Thank you very much for your attention on this question! By loading the mat file that i attached to this post into 2020b, I just drag the mat file which yeilds load('Y:\Practice Project Cobb County 2019\Cobb county 2019 practice project - answer - V2 Testing\configV2.mat') in the command line. But I dont see any warning popped up see the below attachment 1 named as configV2OpenIn2020b.png. Even though I used load('....','-mat'), by telling Matlab using the "-mat" language (I assumed this is the language you meant, sorry, correct me if i misunderstood this), this config.defects field is still empty.

If I load exactly the same file in 2018b (which was originally created by 2018b) by doing the same above. It shows that the config.defects does have an array of struct which I wanted to get value from as shown below, and also attached as configV2OpenIn2018b.png

This 1X89 Defect has a deep structure as shown below

Any suggestions on why this is happening? Thank you!

[Steven Lord]

Where are the Defects, DefectReport, and DefectContour classes defined? Are those class files on the MATLAB path or in the current directory when you try to load the MAT-file in release R2020b? If they are not, what happens when you put them in a directory on the path or in the current directory and try to load the file again?

[Zhao Ren]

It's loading perfectly with the path included. Thank you so much for guiding to find the cure! Please bear with me with another question. The configV2.mat is saved from standalone program compiled under R2018b. If the user of the program wants to develop some work using this configV2 in Matlab, but not allowed to have the source code of the program, what is the way for the user to access the values of this data saved in this configV2? Bear with me, I am not coming from a computer background which could be easier to find a clue. Is there something need to be created and give to the user so that he/she can call a program to allow definition of the mat file. Appreciated if you can shed some light to this!! Joann

[Steven Lord]

So you want users to be able to load data variables of the Defects class without being able to see or modify the Defects class? See this documentation page.

[Zhao Ren]

Yes, and thank you very much. This documentation is very helpful!