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topic is already advertised as md5sum [...] and datatype [...]

asked 2017-04-05 19:15:47 -0500

SRD gravatar image

updated 2017-04-05 19:37:39 -0500

I'm trying to get output from a remote node to the /rosout topic and view it with 'rostopic echo rosout' running on the master. I have a roscore running on hostA brought up by starting roslaunch. On hostB, I have a node built from roscpp.

My nodes code is as follows:

int func1()
    if (ros::console::set_logger_level(ROSCONSOLE_DEFAULT_NAME,
        ros::console::levels::Debug) ) {

    map<string, string> remap;
    remap.emplace("__ip", get_ip());
    remap.emplace("__master", get_master_uri());

    ros::init(remap, "test-node");

    while (!ros::master::check()) {

    nh = boost::make_shared<ros::NodeHandle>();


    return 0;

int func2()
    ROS_INFO("point A");

    ros::Publisher pub =
        nh->advertise<std_msgs::String>("rosout", 1000);

    ROS_INFO("point B");

    std_msgs::String msg;
    stringstream ss;
    ss << "Using stringstream."; = ss.str();

    ROS_INFO("point C"); 
    ROS_INFO_STREAM("ss data: " <<;

    ROS_INFO_STREAM("ROS Node Namespace: " << ros::this_node::getNamespace());
    ROS_INFO_STREAM("ROS Node Name: " << ros::this_node::getName());

    ROS_INFO("point 4");

    return 0;    

The only thing I ever see show up on the master node is "point A", "point B" never prints and I get the following message on the master node.

Tried to advertise on topic [/rosout] with md5sum [992ce8a1687cec8c8bd883ec973ca4131] and datatype [std_msgs/String], but the topic is already advertised as md5sum [acffd30cd6b6de30f120938c17c593fb] and datatype [rosgraph_msgs/Log]

No where's have I used a datatype of rosgraph_msgs and I'm not sure why the message says so. rqt_console shows me the message is coming from the node "test-node" as an error. Sometimes the "point A" message will come through with severity 'Info' and shows up properly, but won't go beyond the error above.

Also, how is it that ROS_INFO("point A") shows up on the /rosout of the master, yet the topic hasn't even been advertised yet?


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answered 2017-04-05 19:44:52 -0500

ahendrix gravatar image

The rosout topic is advertised by ros::init as part of the node setup; you don't need to advertise on it yourself.

In addition, ROS_INFO and the associated logging macros already handle publishing to rosout.

The publisher you've created conflicts with the default publisher, which is why you're getting this error message.

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Asked: 2017-04-05 19:15:47 -0500

Seen: 652 times

Last updated: Apr 05 '17