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### Subscribe from C++ external file

Hi!,

I am a new user of Gazebo and maybe this is a trivial question but I was trying to subscribe a topic from a c++ file, so I basically followed the custom messages tutorial. If I have a plugin and want to subscribe a topic the line that I need is:

subJointStates = nodeController->Subscribe("~/robot/JointState",&UpdateJointState,this);


When I tried to subscribe from the c++ file, I can't use "this", since I don't have a class, I have tried replacing "this" with a boolean value, because the declaration of Subscribe wants a boolean.

I tried both of them

subJointStates = nodeController->Subscribe("~/robot/JointState",&UpdateJointState,true);
subJointStates = nodeController->Subscribe("~/robot/JointState",&UpdateJointState,false);


But, looks like it's not working, should I try a different way to subscribe from a C++ External File?

Thank you,

Victor