Robot Operating System——创建可执行文件项目的步骤

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之前我们看到ROS2中，有的Node的实现逻辑存在于动态库中，而动态库又有隐式加载和手动加载等几种模式。这些例子都比较复杂。本文将介绍如何从0到1创建一个最简单的工程，其Node都在可执行文件中，以保证过程的清晰。

初始化环境

在《Robot Operating System——深度解析自动隐式加载动态库的运行模式》一文中，我们展现了ROS2可执行文件的链接指令。可以看到它依赖了很多ROS2环境相关的动态库，所以我们在创建工程之前也要初始化环境。

source /opt/ros/jazzy/setup.bash

关于环境的安装可以参见《Robot Operating System——Ubuntu上以二进制形式安装环境》。

创建Package

ros2 pkg create --build-type ament_cmake --license Apache-2.0 two_node_pipeline

可以看到ros2帮我们创建好了相关的目录结构

剩下的事就是我们要填充这个工程。

代码

在two_node_pipeline/src目录下新建一个main.cpp文件。
代码我们直接借用https://github.com/ros2/demos/blob/jazzy/intra_process_demo/src/cyclic_pipeline/cyclic_pipeline.cpp的源码。它直接在一个可执行文件中编译了两个Node。

// Copyright 2015 Open Source Robotics Foundation, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.#include <chrono>
#include <cinttypes>
#include <cstdio>
#include <memory>
#include <string>
#include <utility>#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/int32.hpp"using namespace std::chrono_literals;// Node that produces messages.
struct Producer : public rclcpp::Node
{Producer(const std::string & name, const std::string & output): Node(name, rclcpp::NodeOptions().use_intra_process_comms(true)){// Create a publisher on the output topic.pub_ = this->create_publisher<std_msgs::msg::Int32>(output, 10);std::weak_ptr<std::remove_pointer<decltype(pub_.get())>::type> captured_pub = pub_;// Create a timer which publishes on the output topic at ~1Hz.auto callback = [captured_pub]() -> void {auto pub_ptr = captured_pub.lock();if (!pub_ptr) {return;}static int32_t count = 0;std_msgs::msg::Int32::UniquePtr msg(new std_msgs::msg::Int32());msg->data = count++;printf("Published message with value: %d, and address: 0x%" PRIXPTR "\n", msg->data,reinterpret_cast<std::uintptr_t>(msg.get()));pub_ptr->publish(std::move(msg));};timer_ = this->create_wall_timer(1s, callback);}rclcpp::Publisher<std_msgs::msg::Int32>::SharedPtr pub_;rclcpp::TimerBase::SharedPtr timer_;
};// Node that consumes messages.
struct Consumer : public rclcpp::Node
{Consumer(const std::string & name, const std::string & input): Node(name, rclcpp::NodeOptions().use_intra_process_comms(true)){// Create a subscription on the input topic which prints on receipt of new messages.sub_ = this->create_subscription<std_msgs::msg::Int32>(input,10,[](std_msgs::msg::Int32::UniquePtr msg) {printf(" Received message with value: %d, and address: 0x%" PRIXPTR "\n", msg->data,reinterpret_cast<std::uintptr_t>(msg.get()));});}rclcpp::Subscription<std_msgs::msg::Int32>::SharedPtr sub_;
};int main(int argc, char * argv[])
{setvbuf(stdout, NULL, _IONBF, BUFSIZ);rclcpp::init(argc, argv);rclcpp::executors::SingleThreadedExecutor executor;auto producer = std::make_shared<Producer>("producer", "number");auto consumer = std::make_shared<Consumer>("consumer", "number");executor.add_node(producer);executor.add_node(consumer);executor.spin();rclcpp::shutdown();return 0;
}

添加依赖（package.xml）

package.xml 是 ROS 2 包的元数据文件，定义了包的基本信息和依赖关系。

打开two_node_pipeline/package.xml，添加代码中include头文件（#include "rclcpp/rclcpp.hpp" #include "std_msgs/msg/int32.hpp"）所依赖的其他库。

  <depend>rclcpp</depend><depend>std_msgs</depend>

完整文件如下

<?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>two_node_pipeline</name><version>0.0.0</version><description>TODO: Package description</description><maintainer email="f304646673@gmail.com">fangliang</maintainer><license>Apache-2.0</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>

修改编译描述

find_package寻找依赖库

再打开two_node_pipeline/CMakeLists.txt中添加上述头文件（#include "rclcpp/rclcpp.hpp" #include "std_msgs/msg/int32.hpp"）所依赖的库

find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)

在 CMake 中，find_package 命令用于查找并加载外部包或库。它的主要作用如下：

• 查找包：find_package 会在系统中查找指定的包或库，并加载其配置文件。这些配置文件通常包含包的路径、库文件、头文件等信息。

• 设置变量：如果找到包，find_package 会设置一些变量，这些变量可以在后续的 CMake 脚本中使用。例如，<PackageName>_FOUND 变量会被设置为 TRUE，表示找到了包。

• 导入目标：一些包会定义 CMake 导入目标（imported targets），这些目标可以直接在 target_link_libraries 等命令中使用。

指定代码路径和编译类型（可执行文件/动态库）

设定编译结果名称

set(EXECUTABLE_NAME "two_node_pipeline")

指定编译结果是可执行文件

# Collect all source files in this directory
file(GLOB SOURCES "src/*.cpp")# Add the executable target
add_executable(${EXECUTABLE_NAME} ${SOURCES})

链接依赖的库

最后将代码中用到的库（#include "rclcpp/rclcpp.hpp" #include "std_msgs/msg/int32.hpp"）链接到可执行文件中。

ament_target_dependencies(${EXECUTABLE_NAME} rclcpp std_msgs)

完整文件

cmake_minimum_required(VERSION 3.8)
project(two_node_pipeline)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)
# uncomment the following section in order to fill in
# further dependencies manually.
# find_package(<dependency> REQUIRED)find_package(rclcpp REQUIRED)
find_package(std_msgs REQUIRED)set(EXECUTABLE_NAME "two_node_pipeline")# Collect all source files in this directory
file(GLOB SOURCES "src/*.cpp")# Add the executable target
add_executable(${EXECUTABLE_NAME} ${SOURCES})ament_target_dependencies(${EXECUTABLE_NAME} rclcpp std_msgs)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 filesset(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 filesset(ament_cmake_cpplint_FOUND TRUE)ament_lint_auto_find_test_dependencies()
endif()ament_package()

编译

cd two_node_pipeline/build
cmake ..
make

测试

./two_node_pipeline 

总结

1. 初始化环境source /opt/ros/jazzy/setup.bash，以保证ROS2的基础动态库路径在系统PATH中。
2. 通过`ros2 pkg create --build-type ament_cmake --license Apache-2.0 <YOUR-Folder-Name>'创建目录结构和基础文件。
3. 填充代码。
4. package.xml中添加代码中显式依赖的库。
5. CMakeLists.txt中寻找和链接代码中显式依赖的库。

参考资料

• https://docs.ros.org/en/rolling/Tutorials/Beginner-Client-Libraries/Creating-A-Workspace/Creating-A-Workspace.html#new-directory

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