ROS官方消息说明

ROS2中std_msgs消息包含类型

https://docs.ros2.org/latest/api/std_msgs/msg/

std_msgs/msg/Header Message
std_msgs/msg/Header数据格式：

builtin_interfaces/msg/Time stamp #Two-integer timestamp that is expressed as seconds and nanoseconds.
string frame_id # Transform frame with which this data is associated.

数据说明

builtin_interfaces/msg/Time stamp 
#时间戳，主要由秒和纳秒两部分构成
stamp有两个成员，分别为sec秒和nanosec纳秒
# int32 values.
int32 sec
#nanoseconds[0, 10e9).
uint32 nanosec

使用ros2标准的Header案例

程序实现功能：生成一个名字为test的节点，该节点主要发送两个话题数据，类型分别为std_msgs/msg/header，std_msgs/msg/string，实现代码如下：

#include <iostream>
#include <rclcpp/rclcpp.hpp>
#include <std_msgs/msg/header.hpp>
#include <std_msgs/msg/string.hpp>
#include <string>
#include <memory>
#include <chrono>

using namespace std;

class node:public rclcpp::Node{
public:
    node(std::string name):Node(name){
    pub_head = this->create_publisher<std_msgs::msg::Header>("header_topic", 10);
    pub_string = this->create_publisher<std_msgs::msg::String>("string_topic", 10);
    }
    rclcpp::Publisher<std_msgs::msg::Header>::SharedPtr pub_head;
    rclcpp::Publisher<std_msgs::msg::String>::SharedPtr pub_string;

};

int main(int argc, char**argv){
    rclcpp::init(argc, argv);
    std::shared_ptr<node> node_ptr =  std::make_shared<node>("test");
    std_msgs::msg::Header pub_header;
    std_msgs::msg::String pub_string;
    int i = 0;
    rclcpp::Time t;
    while(rclcpp::ok()){
    	i++;
        pub_string.data = "num" + std::to_string(i);
        pub_header.frame_id = "world";
        // pub_header.stamp = std::chrono::system_clock::now(); 
        pub_header.stamp = node_ptr->now();
        node_ptr->pub_head->publish(pub_header);
        node_ptr->pub_string->publish(pub_string);
        sleep(1);
    }
    cout<<"hello_world!"<<endl;
}

代码解释

pub_header.stamp = node_ptr->now();
此处通过节点node_ptr来获取时间戳信息，并将值赋给要发布变量；

ROS获取时间的方式有很多种，具体可以参考一下内容：
https://blog.csdn.net/shoufei403/article/details/125955660
https://docs.ros2.org/bouncy/api/rclcpp/classrclcpp_1_1_time.html
推荐知乎ROS2获取当前系统时间的方法：
https://zhuanlan.zhihu.com/p/545431541?utm_id=0

测试结果