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How do I dynamically link an SimpleActionClient to a SimpleActionServer?

asked 2016-06-10 03:02:36 -0500

BobF gravatar image

I have a node that needs to dynamically discover and link to multiple servers. Each of my action servers are publishing/subscribing to the below topics...

/{link_name}/{node_name}/goal , /{link_name}/{node_name}/result , etc...

By inquires to the ROS Parameter Server, I can determine what strings to plug in for {link_name} and {node_name}. But, my client is having trouble dynamically opening the servers. ServerConnection is a Class that represents a connection to a server. Its header file looks like...

ServerConnection class {
     ServerConnection( );
    bool openActionClient(std::string linkNode);
    actionlib::SimpleActionClient<mot_ctl_dvr::calibrateaction> *actionClient;

The connection is opened in the openActionClient() method. In the .cpp file...

bool ServerConnection::openActionClient(std::string linkNode) {
    // linkNode = "{link_name}/{node_name}"
    // <mot_ctl_dvr::CalibrateAction> is the namesace::action name that the servers use.
    actionClient = new actionlib::SimpleActionClient<mot_ctl_dvr::CalibrateAction>::SimpleActionClient (linkNode, true);

The compile error is...
/home/bob/Qt4Projects/robot_calibrator/serverconnection.cpp:40: error: expected type-specifier
    new actionlib::SimpleActionClient<mot_ctl_dvr::CalibrateAction>::SimpleActionClient
I haven't found any example code that invokes the SimpleActionClient constructor dynamically (using new).
Has anyone tried to invoke the constructor using this dynamic form?
What is the secret to coding it?

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2 Answers

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answered 2016-07-09 18:50:58 -0500

BobF gravatar image

I found the solution. The statement should be...
actionClient = new actionlib::SimpleActionClient<mot_ctl_dvr::CalibrateAction> (linkNode, true);

However, coding the above results in two pages of compiler messages. A close reading of the messages found that it wasn't as bad as the volume of messages indicated. There were 3 warning messages and nothing more severe. All of the messages were "unused parameter" warnings caused by actionlib included templates. Normally ROS include libraries are clean of these types of warnings, but apparently actionlib missed these.
The 3 warnings were caused by two actionlib include files...
/opt/ros/indigo/include/actionlib/enclosure_deleter.h line 60.
    void oerator() (Member * member_ptr)
    where member_ptr is not referenced.
And, /opt/ros/indigo/include/actionlib/managed_list.h line 92.
    void operator() (void * ptr)
    where ptr is not referenced.
I edited my system's copy of these files to suppress the messages by adding...
"(void) member_ptr;" and "(void) ptr;" to the respective functions.

I delayed reporting resolution of this question until I was sure that my dynamically allocated SimpleActionClient was fully operational and that my fixes weren't masking other errors. The client seems to be working fine.
These files should be fixed by the developers.

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answered 2018-02-15 05:22:34 -0500

declare the instance as pointer variable to the class member, and use the new to create the instance whenever it is required in the class.

for example:

class AC{

ActionClient ac_;

AC(string name) {

ac_= new ActionClient(name, true);

} };

make sure you clear the pointer after use. I am beginner too. please correct if I have any mistakes.

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Asked: 2016-06-10 03:02:36 -0500

Seen: 572 times

Last updated: Jul 09 '16