古月居 ROS 21 讲

5、话题消息的订阅与使用

1)完成数据接口的定义：在learning topic中创建msg，打开终端设置

string name
uint8 sex
uint8 age
uint8 unknown = 0
uint8 male = 1
uint8 female = 2

2）根据数据接口定义设置编译规则
➢ 在package.xml中添加功能包依赖
<build_depend>message_generation</build_depend>编译依赖
<exec_depend>message_runtime</exec_depend>运行依赖

➢ 在CMakeLists.txt添加编译选项
• message_generation
• add_message_files(FILES Person.msg)接口
generate_messages(DEPENDENCIES std_msgs) ROS已经有的库
• message_runtime
由.msg编译生成的代码文件.h

// Generated by gencpp from file learning_topic/Person.msg
// DO NOT EDIT!


#ifndef LEARNING_TOPIC_MESSAGE_PERSON_H
#define LEARNING_TOPIC_MESSAGE_PERSON_H


#include <string>
#include <vector>
#include <map>

#include <ros/types.h>
#include <ros/serialization.h>
#include <ros/builtin_message_traits.h>
#include <ros/message_operations.h>


namespace learning_topic
{
template <class ContainerAllocator>
struct Person_
{
  typedef Person_<ContainerAllocator> Type;

  Person_()
    : name()
    , sex(0)
    , age(0)  {
    }
  Person_(const ContainerAllocator& _alloc)
    : name(_alloc)
    , sex(0)
    , age(0)  {
  (void)_alloc;
    }



   typedef std::basic_string<char, std::char_traits<char>, typename ContainerAllocator::template rebind<char>::other >  _name_type;
  _name_type name;

   typedef uint8_t _sex_type;
  _sex_type sex;

   typedef uint8_t _age_type;
  _age_type age;



  enum {
    unknown = 0u,
    male = 1u,
    female = 2u,
  };


  typedef boost::shared_ptr< ::learning_topic::Person_<ContainerAllocator> > Ptr;
  typedef boost::shared_ptr< ::learning_topic::Person_<ContainerAllocator> const> ConstPtr;

}; // struct Person_

typedef ::learning_topic::Person_<std::allocator<void> > Person;

typedef boost::shared_ptr< ::learning_topic::Person > PersonPtr;
typedef boost::shared_ptr< ::learning_topic::Person const> PersonConstPtr;

// constants requiring out of line definition

template<typename ContainerAllocator>
std::ostream& operator<<(std::ostream& s, const ::learning_topic::Person_<ContainerAllocator> & v)
{
ros::message_operations::Printer< ::learning_topic::Person_<ContainerAllocator> >::stream(s, "", v);
return s;
}

} // namespace learning_topic

namespace ros
{
namespace message_traits
{



// BOOLTRAITS {'IsFixedSize': False, 'IsMessage': True, 'HasHeader': False}
// {'learning_topic': ['/home/ubuntu/catkin_ws/src/learning_topic/msg'], 'std_msgs': ['/opt/ros/kinetic/share/std_msgs/cmake/../msg']}

// !!!!!!!!!!! ['__class__', '__delattr__', '__dict__', '__doc__', '__eq__', '__format__', '__getattribute__', '__hash__', '__init__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_parsed_fields', 'constants', 'fields', 'full_name', 'has_header', 'header_present', 'names', 'package', 'parsed_fields', 'short_name', 'text', 'types']




template <class ContainerAllocator>
struct IsFixedSize< ::learning_topic::Person_<ContainerAllocator> >
  : FalseType
  { };

template <class ContainerAllocator>
struct IsFixedSize< ::learning_topic::Person_<ContainerAllocator> const>
  : FalseType
  { };

template <class ContainerAllocator>
struct IsMessage< ::learning_topic::Person_<ContainerAllocator> >
  : TrueType
  { };

template <class ContainerAllocator>
struct IsMessage< ::learning_topic::Person_<ContainerAllocator> const>
  : TrueType
  { };

template <class ContainerAllocator>
struct HasHeader< ::learning_topic::Person_<ContainerAllocator> >
  : FalseType
  { };

template <class ContainerAllocator>
struct HasHeader< ::learning_topic::Person_<ContainerAllocator> const>
  : FalseType
  { };


template<class ContainerAllocator>
struct MD5Sum< ::learning_topic::Person_<ContainerAllocator> >
{
  static const char* value()
  {
    return "8361f88618d6779bd872f0ba928ced56";
  }

  static const char* value(const ::learning_topic::Person_<ContainerAllocator>&) { return value(); }
  static const uint64_t static_value1 = 0x8361f88618d6779bULL;
  static const uint64_t static_value2 = 0xd872f0ba928ced56ULL;
};

template<class ContainerAllocator>
struct DataType< ::learning_topic::Person_<ContainerAllocator> >
{
  static const char* value()
  {
    return "learning_topic/Person";
  }

  static const char* value(const ::learning_topic::Person_<ContainerAllocator>&) { return value(); }
};

template<class ContainerAllocator>
struct Definition< ::learning_topic::Person_<ContainerAllocator> >
{
  static const char* value()
  {
    return "string name\n\
uint8 sex\n\
uint8 age\n\
uint8 unknown = 0\n\
uint8 male = 1\n\
uint8 female = 2\n\
";
  }

  static const char* value(const ::learning_topic::Person_<ContainerAllocator>&) { return value(); }
};

} // namespace message_traits
} // namespace ros

namespace ros
{
namespace serialization
{

  template<class ContainerAllocator> struct Serializer< ::learning_topic::Person_<ContainerAllocator> >
  {
    template<typename Stream, typename T> inline static void allInOne(Stream& stream, T m)
    {
      stream.next(m.name);
      stream.next(m.sex);
      stream.next(m.age);
    }

    ROS_DECLARE_ALLINONE_SERIALIZER
  }; // struct Person_

} // namespace serialization
} // namespace ros

namespace ros
{
namespace message_operations
{

template<class ContainerAllocator>
struct Printer< ::learning_topic::Person_<ContainerAllocator> >
{
  template<typename Stream> static void stream(Stream& s, const std::string& indent, const ::learning_topic::Person_<ContainerAllocator>& v)
  {
    s << indent << "name: ";
    Printer<std::basic_string<char, std::char_traits<char>, typename ContainerAllocator::template rebind<char>::other > >::stream(s, indent + "  ", v.name);
    s << indent << "sex: ";
    Printer<uint8_t>::stream(s, indent + "  ", v.sex);
    s << indent << "age: ";
    Printer<uint8_t>::stream(s, indent + "  ", v.age);
  }
};

} // namespace message_operations
} // namespace ros

#endif // LEARNING_TOPIC_MESSAGE_PERSON_H

创建person_publisher与person_subscriber

Publisher

/**
 * 该例程将发布/person_info话题，自定义消息类型learning_topic::Person
 */

#include <ros/ros.h>
#include "learning_topic/Person.h"
int main(int argc, char **argv)
{
    // ROS节点初始化
    ros::init(argc, argv, "person_publisher");

    // 创建节点句柄
    ros::NodeHandle n;

    // 创建一个Publisher，发布名为/person_info的topic，消息类型为learning_topic::Person，队列长度10
    ros::Publisher person_info_pub = n.advertise<learning_topic::Person>("/person_info", 10);

    // 设置循环的频率
    ros::Rate loop_rate(1);

    int count = 0;
    while (ros::ok())
    {
        // 初始化learning_topic::Person类型的消息
        learning_topic::Person person_msg;
                person_msg.name = "Tom";
                person_msg.age  = 18;
                person_msg.sex  = learning_topic::Person::male;

        // 发布消息
                person_info_pub.publish(person_msg);

        ROS_INFO("Publish Person Info: name:%s  age:%d  sex:%d",
                                  person_msg.name.c_str(), person_msg.age, person_msg.sex);

        // 按照循环频率延时
        loop_rate.sleep();
    }

    return 0;
}

Subscriber

/**
 * 该例程将订阅/person_info话题，自定义消息类型learning_topic::Person
 */

#include <ros/ros.h>
#include "learning_topic/Person.h"

// 接收到订阅的消息后，会进入消息回调函数
void personInfoCallback(const learning_topic::Person::ConstPtr& msg)
{
    // 将接收到的消息打印出来
    ROS_INFO("Subcribe Person Info: name:%s  age:%d  sex:%d",
                         msg->name.c_str(), msg->age, msg->sex);
}

int main(int argc, char **argv)
{
    // 初始化ROS节点
    ros::init(argc, argv, "person_subscriber");

    // 创建节点句柄
    ros::NodeHandle n;

    // 创建一个Subscriber，订阅名为/person_info的topic，注册回调函数personInfoCallback
    ros::Subscriber person_info_sub = n.subscribe("/person_info", 10, personInfoCallback);

    // 循环等待回调函数
    ros::spin();

    return 0;
}

3）编译代码

如何配置CMakeLists.txt中的编译规则
• 设置需要编译的代码和生成的可执行文件；
• 设置链接库；
• 添加依赖项。

add_executable(person_publisher src/person_publisher.cpp)
target_link_libraries(person_publisher ${catkin_LIBRARIES})
add_dependencies(person_publisher ${PROJECT_NAME}_generate_messages_cpp)

add_executable(person_subscriber src/person_subscriber.cpp)
target_link_libraries(person_subscriber ${catkin_LIBRARIES})
add_dependencies(person_subscriber ${PROJECT_NAME}_generate_messages_cpp)
拷贝到CMakeLists.txt

$ cd ~/catkin_ws
$ catkin_make
$ source devel/setup.bash
$ roscore
$ rosrun learning_topic person_subscriber
$ rosrun learning_topic person_publisher

关掉ROSMaster也不会影响发送与接受