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how to print name of elements of ros message

asked 2016-06-02 07:17:43 -0600

JanOr gravatar image

updated 2016-06-02 07:35:08 -0600

Hey, I would like to print the elements of ros messages dynamically, with a function similar to:

template <typename M>
void printElements()const{
            const boost::shared_ptr<M> msgPtr;
                Extract element table 
               cout<< how can I access the name of the elements here?<<endl;

How can I extract the message elements so that when I execute


,I get for the example of a "geometry_msgs/PoseStamped" Message:


Do you have an idea how I can dynamically access the name, e.g. "pose.position.x","pose.position.y","pose.position.z", etc. For other message type, the printout shall be accordingly. Thank you very much for any ideas of solving this issue!

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Do you need it in C++? This is probably going to be a bit involved, possibly including parsing the created header files. It would be much easier in python as python objects still contain the variable names.

NEngelhard gravatar image NEngelhard  ( 2016-06-02 15:08:28 -0600 )edit

Thanks a lot. Yes unfortunately I need it in c++. That's not good news. I thought that roscpp makes the variable names somewhere accessible. Thank you very much.

JanOr gravatar image JanOr  ( 2016-06-03 10:10:56 -0600 )edit

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answered 2016-06-03 10:29:01 -0600

kramer gravatar image

updated 2016-06-10 09:18:42 -0600

You might want to look into classes in the topic tools package. I think that the ShapeShifter class provides the functionality you're looking for.

Edit: adding a sketch of example code

// might need additional TransportHints parameter?
ros::Subscriber g_sub = nh.subscribe("my_topic", 10, &in_cb);

void in_cb(const ros::MessageEvent<ShapeShifter>& ev) {
    boost::shared_ptr<ShapeShifter const> const &ssmsg = ev.getConstMessage();

    ROS_INFO("publisher: [%s]", ev.getPublisherName().c_str());
    ROS_INFO("   md5sum: [%s]", ssmsg->getMD5Sum().c_str());
    ROS_INFO(" datatype: [%s]", ssmsg->getDataType().c_str());
    ROS_INFO("     defn: [%s]", ssmsg->getMessageDefinition().c_str());
    ROS_INFO(" msg size: %u", ssmsg->size());

This is a snip-job of old code I was playing with in Hydro, so I'm not sure it's current. However, it should be enough to point you (further) in a useful direction.

Edit2: Probably should've mentioned -- in case it's not clear, the specific thing you'll be concerned with is the getMessageDefinition method. You'll have to parse the returned string as you see fit.

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Hey, thanks for the idea. Could you specify this idea a bit more. As I understood, the shapeshifter class can act as a generic message class. Nevertheless I don't now how to show the message variables (e.g. "pose.position.x") and not the message data (e.g. "1.23"). Thanks a lot for your help.

JanOr gravatar image JanOr  ( 2016-06-06 03:14:57 -0600 )edit

Edited answer with a(n old) code demo snippet. Hope that helps.

kramer gravatar image kramer  ( 2016-06-10 08:01:35 -0600 )edit

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Asked: 2016-06-02 07:17:43 -0600

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Last updated: Jun 10 '16