rosgenmsg(folderpath) from custom ros msgs add on causes Index exceeds the number of array elements (0).

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Daniel Levy 2020-3-27

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评论： RIKUTO OSHITA 2024-5-26

Hello,

I'm trying to get Matlab to be able to use some custom ROS msgs from a ROS package that follows the required structure has worked in other environments. I've followed the instructions at https://www.mathworks.com/help/ros/ug/create-custom-messages-from-ros-package.html but will get a 'Index exceeds the number of array elements (0).' Error on the rosgenmsg(folderpath)

Any one run into this issue before or is this a bug.

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Dhananjay Kumar 2020-3-30

Hey daniel, Can you write the complete error message you see or attach a snip?

Daniel Levy 2020-3-30

在 MATLAB Online 中打开

The code I used was straight from the instructions at https://www.mathworks.com/help/ros/ug/create-custom-messages-from-ros-package.html I also made sure that folder exists.

examplePackages = fullfile(fileparts(which('rosgenmsg')), 'examples', 'packages');
userFolder = 'C:\MATLAB\CustomMessages\';
copyfile(examplePackages, userFolder)
folderpath = userFolder;
rosgenmsg(folderpath)

Error message is below, breaks at rosgenmsg(folderpath)

Error using ROSScratchPad (line 8)
Index exceeds the number of array elements (0).

Thanks,

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Answer 1

Cam Salzberger 2020-3-30

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Daniel,

This kind of error message generally comes up (in any MATLAB product) when you are trying to call a function but have shadowed the function name with a variable name. For example, if you do this:

rosgenmsg = 1;
myPath = 'C:\ros';
rosgenmsg(myPath)

MATLAB is trying to index into the variable "rosgenmsg" using the character values in "myPath" as index values. Since 'C' is valued at a larger index than the length of "rosgenmsg", you see this error.

Run this command to see if you have "rosgenmsg" shadowed by a variable name:

which -all rosgenmsg

-Cam

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Cam Salzberger 2020-3-31

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Hmm, we're now exploring odd territory. If "rosgenmsg" were indeed a variable, then I would expect to see an error message more like this:

Index exceeds the number of array elements (1).
'rosgenmsg' appears to be both a function and a variable. If this is unintentional, use 'clear rosgenmsg' to remove the variable 'rosgenmsg' from the workspace.

And this would be result of which -all rosgenmsg:

rosgenmsg is a variable.
C:\ProgramData\MATLAB\SupportPackages\R2019b\toolbox\ros\supportpackages\roscustommsg\rosgenmsg.m  % Shadowed

If it was calling the correct rosgenmsg, but there was some issue with it, I'd expect to see a stack trace that shows at which line in rosgenmsg there was an issue. However, a lot of the ROS 1 functionality uses custom error messages which can sometimes disguise exactly where the error occurs in the toolbox code. Try giving this a shot, and see if the report looks more useful:

try
    rosgenmsg(folderpath)
catch ME
    getCustomReport(ME)
end

Another thing to try after that is to simply debug-break at first point the error occurs. Sometimes this is a bit down in the weeds, but it can help situations like this. First run this:

dbstop if error

Then run your code. See where the error is occurring, what the error is, and what the workspace looks like while in debug mode.

-Cam

Cam Salzberger 2020-3-31

That's good to know, and hopefully anyone else running into the same issue can find it now. Thanks for posting the answer!

RIKUTO OSHITA 2024-5-26

Hi,Cam,

I encountered the same error when trying to create a custom message for xarm_ros.

What do you think this error cause?

error is follows.

'Index exceeds the number of array elements. Index must not exceed 1.

error: ros.internal.MessageParser/getUpdatedMessageFileContents (行 557)

value = currentLine{2};

If you have a solution, I would appreciate hearing from you.

thank you.

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