ROS2机器人编程简述humble-第二章-DEVELOPING THE FIRST NODE .2
0.1ROS2机器人编程简述新书推荐-A Concise Introduction to Robot Programming with ROS2
1.1ROS2机器人编程简述humble-第一章-Introduction
2.1ROS2机器人编程简述humble-第二章-First Steps with ROS2 .1
2.2主要内容是全手工创建一个最简单的自定义节点，其实没啥具体功能，主要是对ROS2节点结构有个更好的理解吧。
使用ros2 pkg create这个命令。
其实-h看一下非常清晰明了。
ros2 pkg create -h
usage: ros2 pkg create [-h] [--package-format {2,3}] [--description DESCRIPTION]
[--license LICENSE]
[--destination-directory DESTINATION_DIRECTORY]
[--build-type {cmake,ament_cmake,ament_python}]
[--dependencies DEPENDENCIES [DEPENDENCIES ...]]
[--maintainer-email MAINTAINER_EMAIL]
[--maintainer-name MAINTAINER_NAME] [--node-name NODE_NAME]
[--library-name LIBRARY_NAME]
package_name
Create a new ROS 2 package
positional arguments:
package_name The package name
options:
-h, --help show this help message and exit
--package-format {2,3}, --package_format {2,3}
The package.xml format.
--description DESCRIPTION
The description given in the package.xml
--license LICENSE The license attached to this package; this can be an
arbitrary string, but a LICENSE file will only be generated
if it is one of the supported licenses (pass '?' to get a
list)
--destination-directory DESTINATION_DIRECTORY
Directory where to create the package directory
--build-type {cmake,ament_cmake,ament_python}
The build type to process the package with
--dependencies DEPENDENCIES [DEPENDENCIES ...]
list of dependencies
--maintainer-email MAINTAINER_EMAIL
email address of the maintainer of this package
--maintainer-name MAINTAINER_NAME
name of the maintainer of this package
--node-name NODE_NAME
name of the empty executable
--library-name LIBRARY_NAME
name of the empty library创建一个需要 rclcpp std_msgs，节点名为simple_node，功能包名为my_package的命令如下：
ros2 pkg create my package --dependencies rclcpp std_msgs --node-name simple_node
ros2 pkg create my_package --dependencies rclcpp std_msgs --node-name simple_node
going to create a new package
package name: my_package
destination directory: /home/zhangrelay/ros_ws/book_ros2/src
package format: 3
version: 0.0.0
description: TODO: Package description
maintainer: ['zhangrelay <zhangrelay@todo.todo>']
licenses: ['TODO: License declaration']
build type: ament_cmake
dependencies: ['rclcpp', 'std_msgs']
node_name: simple_node
creating folder ./my_package
creating ./my_package/package.xml
creating source and include folder
creating folder ./my_package/src
creating folder ./my_package/include/my_package
creating ./my_package/CMakeLists.txt
creating ./my_package/src/simple_node.cpp这些都是自动生成的，非常方便，当然也有图形化IDE更加方便使用，后续补充。
tree my_package/
my_package/
├── CMakeLists.txt
├── include
│ └── my_package
├── package.xml
└── src
└── simple_node.cpp
3 directories, 3 filespackage.xml
<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
<name>my_package</name>
<version>0.0.0</version>
<description>TODO: Package description</description>
<maintainer email="zhangrelay@todo.todo">zhangrelay</maintainer>
<license>TODO: License declaration</license>
<buildtool_depend>ament_cmake</buildtool_depend>
<depend>rclcpp</depend>
<depend>std_msgs</depend>
<test_depend>ament_lint_auto</test_depend>
<test_depend>ament_lint_common</test_depend>
<export>
<build_type>ament_cmake</build_type>
</export>
</package>simple_node.cpp
#include <cstdio>
int main(int argc, char ** argv)
{
(void) argc;
(void) argv;
printf("hello world my_package package\n");
return 0;
}参考案例:
#include "rclcpp/rclcpp.hpp"
int main(int argc, char * argv[]) {
rclcpp::init(argc, argv);
auto node = rclcpp::Node::make_shared("simple_node");
rclcpp::spin(node);
rclcpp::shutdown();
return 0;
}•#include“rclcpp/rrcpp.hpp”允许访问C++中的大多数ROS2类型和函数。
•rclcpp::init（argc，argv）从启动此进程的参数中提取ROS2应考虑的任何选项。
•第6行创建ROS2节点。node是名称为simplenode的ROS2节点的std::shared_ptr。
rclcpp::Node类配备了许多别名和静态函数，以简化代码。SharedPtr是std::shared-ptr＜rclcppNode＞的别名，
make shared是std:：make shared＜rclcpp::Node＞的静态方法。
以下行是等效的：
std::shared_ptr<rclcpp::Node> node = std::shared_ptr<rclcpp::Node>(
new rclcpp::Node("simple_node"));
std::shared_ptr<rclcpp::Node> node = std::make_shared<rclcpp::Node>(
"simple_node");
rclcpp::Node::SharedPtr node = std::make_shared<rclcpp::Node>(
"simple_node");
auto node = std::make_shared<rclcpp::Node>("simple_node");
auto node = rclcpp::Node::make_shared("simple_node");•在此代码中，spin阻止程序的执行，因此不会立即终止。其重要功能将在后续示例中解释。
•shutdown管理在下一行程序结束之前节点的关闭。
CMakelist.txt
cmake_minimum_required(VERSION 3.8)
project(my_package)
if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
add_compile_options(-Wall -Wextra -Wpedantic)
endif()
# find dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)
add_executable(simple_node src/simple_node.cpp)
target_include_directories(simple_node PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
$<INSTALL_INTERFACE:include>)
target_compile_features(simple_node PUBLIC c_std_99 cxx_std_17) # Require C99 and C++17
ament_target_dependencies(
simple_node
"rclcpp"
"std_msgs"
)
install(TARGETS simple_node
DESTINATION lib/${PROJECT_NAME})
if(BUILD_TESTING)
find_package(ament_lint_auto REQUIRED)
# the following line skips the linter which checks for copyrights
# comment the line when a copyright and license is added to all source files
set(ament_cmake_copyright_FOUND TRUE)
# the following line skips cpplint (only works in a git repo)
# comment the line when this package is in a git repo and when
# a copyright and license is added to all source files
set(ament_cmake_cpplint_FOUND TRUE)
ament_lint_auto_find_test_dependencies()
endif()
ament_package()编译：colcon build --symlink-install
[ 50%] Building CXX object CMakeFiles/simple_node.dir/src/simple_node.cpp.o
[100%] Linking CXX executable simple_node
[100%] Built target simple_node测试（执行）：ros2 run my_package simple_node
一个最简单的ROS2功能包完工。