ros如何获取topic中的md5sum及类型等

    string doQueue(const ros::MessageEvent<topic_tools::ShapeShifter const>& msg_event, string const& topic, shared_ptr<ros::Subscriber> subscriber, shared_ptr<int> count) {

        static int once = 0;
        ros::Time rectime = ros::Time::now();
        rosbag::OutgoingMessage  out(topic, msg_event.getMessage(), msg_event.getConnectionHeaderPtr(), rectime);

        std::cout<<"topic MD5:  "<<out.msg->getMD5Sum()<<"  dataType:   "<<out.msg->getDataType()<<
                   " getMessageDefinition   "<<out.msg->getMessageDefinition()<<
                   "    size:    "<<out.connection_header->size()
                <<std::endl;
        if(once==0)
        {
            ros::NodeHandle node;
            if(static_cast<std::string>(ros::message_traits::MD5Sum<msgs_ht::Track_Control>::value()) ==out.msg->getMD5Sum())
            {
                  Track_sub  = node.subscribe("/track_ctrl", 1000, &RosCommunication::track_listen_back<msgs_ht::Track_Control::ConstPtr>,this);
            }
            else if(static_cast<std::string>(ros::message_traits::MD5Sum<msgs_ht1::Track_Control>::value()) ==out.msg->getMD5Sum())
            {
                    Track_sub   = node.subscribe("/track_ctrl", 1000, &RosCommunication::track_listen_back<msgs_ht1::Track_Control::ConstPtr>,this);
            }
            ReadMD5.insert(map<string,string>::value_type (out.msg->getMD5Sum(),"/track_ctrl"));
            once=1;
        }
        return out.msg->getMD5Sum();

    }



    template<typename T>
    double getTopicInfo(string const &topic,T t){
        ROS_INFO("Subscribing to %s", topic.c_str());
        ros::NodeHandle nh;
        shared_ptr<int> count(make_shared<int>(2));

        shared_ptr<ros::Subscriber> sub(make_shared<ros::Subscriber>());

        ros::SubscribeOptions ops;

        ops.topic = topic;
        //ops.queue_size = 100;
        ops.md5sum = ros::message_traits::md5sum<topic_tools::ShapeShifter>();
        ops.datatype = ros::message_traits::datatype<topic_tools::ShapeShifter>();
        ops.helper = boost::make_shared<ros::SubscriptionCallbackHelperT<
            const ros::MessageEvent<topic_tools::ShapeShifter const> &> >(
                boost::bind(t, this, _1, topic, sub, count));
        ros::TransportHints transport_hints;
        ops.transport_hints = transport_hints;
        *sub = nh.subscribe(ops);
    }

    getTopicInfo("/track_ctrl",&RosCommunication::doQueue);

只贴主要代码，感兴趣的人去查找相关文档。