首先在ros下创建一个名位beginner_tutorials的软件包：
$ cd ~/catkin_ws/src $ catkin_create_pkg beginner_tutorials std_msgs rospy roscpp打开beginner_tutorials下的package.xml文件夹，下面是package.xml的代码和我写的注释
<?xml version="1.0"?>//定义version为1.0 <package format="2">//定义format为2 <name>beginner_tutorials</name>//定义name为beginner_tutorials <version>0.0.0</version>//定义version为0.0.0 <description>The beginner_tutorials package</description>//定义描述为The be... <!-- One maintainer tag required, multiple allowed, one person per tag --> <!-- Example: --> <!-- <maintainer email="jane.doe@example.com">Jane Doe</maintainer> --> <maintainer email="aoyin@todo.todo">aoyin</maintainer>//定义email <!-- One license tag required, multiple allowed, one license per tag --> <!-- Commonly used license strings: --> <!-- BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 --> <license>TODO</license> <!-- Url tags are optional, but multiple are allowed, one per tag --> <!-- Optional attribute type can be: website, bugtracker, or repository --> <!-- Example: --> <!-- <url type="website">http://wiki.ros.org/beginner_tutorials</url> --> <!-- Author tags are optional, multiple are allowed, one per tag --> <!-- Authors do not have to be maintainers, but could be --> <!-- Example: --> <!-- <author email="jane.doe@example.com">Jane Doe</author> --> <!-- The *depend tags are used to specify dependencies --> <!-- Dependencies can be catkin packages or system dependencies --> <!-- Examples: --> <!-- Use depend as a shortcut for packages that are both build and exec dependencies --> <!-- <depend>roscpp</depend> -->//定义depend为roscpp <!-- Note that this is equivalent to the following: --> <!-- <build_depend>roscpp</build_depend> -->//定义build_depend为roscpp <!-- <exec_depend>roscpp</exec_depend> -->//定义exec_depend为roscpp <!-- Use build_depend for packages you need at compile time: --> <!-- <build_depend>message_generation</build_depend> --> <!-- Use build_export_depend for packages you need in order to build against this package: --> <!-- <build_export_depend>message_generation</build_export_depend> --> <!-- Use buildtool_depend for build tool packages: --> <!-- <buildtool_depend>catkin</buildtool_depend> -->//定义buildtool为catkin <!-- Use exec_depend for packages you need at runtime: --> <!-- <exec_depend>message_runtime</exec_depend> --> <!-- Use test_depend for packages you need only for testing: --> <!-- <test_depend>gtest</test_depend> --> <!-- Use doc_depend for packages you need only for building documentation: --> <!-- <doc_depend>doxygen</doc_depend> --> <buildtool_depend>catkin</buildtool_depend> <build_depend>roscpp</build_depend> <build_depend>rospy</build_depend> <build_depend>std_msgs</build_depend> <build_export_depend>roscpp</build_export_depend> <build_export_depend>rospy</build_export_depend> <build_export_depend>std_msgs</build_export_depend> <exec_depend>roscpp</exec_depend> <exec_depend>rospy</exec_depend> <exec_depend>std_msgs</exec_depend> <!-- The export tag contains other, unspecified, tags --> <export> <!-- Other tools can request additional information be placed here --> </export> </package>回顾catkin_make的作用：
总结一下整个编译的过程
执行catkin_make执行catkin_workspace。解析catkin_make的参数同时遍历整个工作空间把所有的有package.xml的文件夹添加进软件包列表里面。对每个软件包执行add_subdirectory执行每个软件包内部的CMakeList.txt文件。执行 catkin_package。解析package.xml文件，载入对应的参数。根据依赖参数，载入对应的软件包参数。根据载入参数生成当前软件包的配置文件发现package.xml在第二步将会用到
