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Hey,
I've created a package with only a roscpp dependencies using :
catkin_create_pkg my_package roscpp
On my script, I'm using a Twist message, so I've added :
#include <geometry_msgs/Twist.h>
It works fine and that's the problem... Why does it work since I've not added the std_msgs nor the geometry_msgs dependency? Is this just optional ?
This likely "works" because geometry_msgs will be installed with a regular ROS 1 installation.
So even if you don't add geometry_msgs as a (build) dependency to your CMakeLists.txt and package.xml, /opt/ros/$ROS_DISTRO/include will end up on the include path of your compiler/preprocessor (as part of the include paths exported by some other package you (transitively) depend on), and it will be able to resolve geometry_msgs/Twist.h to /opt/ros/$ROS_DISTRO/include/geometry_msgs/Twist.h.
Now you could ask: "if this works, then why bother adding (build) dependencies to packages at all?"
The answer would be: because you cannot rely on packages like geometry_msgs to always already have been installed.
A ROS 1 installation without geometry_msgs would be perfectly possible, and in that case, when someone tries to build your package, it would fail, as you've not made the dependency on geometry_msgs explicit, and it will not be detected to be missing before the build is started.
Asked: 2022-03-28 04:38:51 -0500
Seen: 84 times
Last updated: Mar 29 '22
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Which dependency entries are you asking about: CMakeLists.txt or package.xml? They have different reasons to exist.