Could not load library (Poco exception = cannot open shared object file: No such file or directory)

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Andreas Schwager
Andreas Schwager on 2 Feb 2021
Answered: Andreas Schwager on 10 Jun 2021
we are using a custom designed ROS topic.
rosgenmsg runs without errors and myTopic is included to rosmsg list.
When calling
rostopic("echo", "myTopic")
there is the error:
Failed to create a ROS subscriber with topic name myTopic and message type myMsgType.
Stepping into rostopic, debugging ends at Subscriber.m Line 547:
returnCall = addSubscriber(obj.InternalNode, ...
serverNodeHandle, ...
obj.MessageInfo.path, ...
topic, ...
obj.MessageInfo.subscriberClassName, ...
callbackFcn, ...
executing this call, the try...catch gets
ex =
MException with properties:
identifier: 'ros:internal:transport:SubscriberError'
message: 'Could not load library (Poco exception = cannot open shared object file: No such file or directory)'
cause: {}
stack: [5×1 struct]
Correction: []
Does anybody know the root-cause of these errors? is included into $LD_LIBRARY_PATH.
We are using Matlab2020b and ROS Melodic.

Answers (2)

Cam Salzberger
Cam Salzberger on 3 Feb 2021
Hello Andreas,
This may be because you have conflicting libraries on your platform's library path. It may be related to this bug, or this one, that were both fixed in R2020b Update 3. Try getting the latest update and see if that resolves the issue.
Also see here for a similar issue with suggested resolutions. Though that question is regarding ROS 2, similar issues may be found in ROS 1.
General advice: If you have defined something outside of MATLAB to explicitly include into your LD_LIBRARY_PATH, that may not be the best course of action (especially if you upgrade your MATLAB installation). It's recommended to allow MATLAB to add its own libraries to the path as needed.
  1 Comment
Andreas Schwager
Andreas Schwager on 16 Feb 2021
Dear Cam,
there is a workarround:
calling a standard ROS topic first, e.g.
topicEcho = rostopic("echo", '/rosout');
and the custom designed ROS topic after, the error does no more happen.
Thanks for yur reply

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Andreas Schwager
Andreas Schwager on 10 Jun 2021
after upgrading to R2020b Update 3 there is the error:
when calling
app.smP.mtSub = rossubscriber('/myTopic',@myTopicCallback);
These lines were running at R2020b Update 2.
Thanks for your help

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