The site is read-only. Please transition to use Robotics Stack Exchange
| ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | ros @ Robotics Stack Exchange |
 | 1 | initial version |
In your example you have ament_export_dependencies(my_target), but that's incorrect. ament_export_dependencies() takes only package names.
In short, ament_target_dependencies() sets up stuff for your package, ament_export_dependencies() and ament_export_interfaces() set up stuff for packages that depend on your package.
When a package calls find_package(MyDependency), CMake looks for a file called mydependency-config.cmake or MyDependency-config.cmake. CMake documentation calls this a ProjectConfig.cmake file. The ProjectConfig.cmake sets up everything another project would need to depend on this one. It sets variables like MyDependency_INCLUDE_DIRS, creates imported targets like MyDependency::somelibrary, and finds packages MyDependency depends on.
First your package needs to use MyDependency when it's being built. ament_target_dependencies(my_target MyDependency) is a helper function that makes sure your executable or library has everything it needs to use MyDependency. It will call target_link_libraries(my_target ${MyDependency_LIBRARIES}), target_include_directories(my_target PUBLIC ${MyDependency_INCLUDE_DIRS}), etc.
Once your package is built/installed, other packages might need MyDependency too. For example, if your package includes <my_depdenency/something.hpp> in a header it installs, then packages that include your header will need to know where MyDependency's headers are too. This is where ament_export_dependencies() comes in . Calling ament_export_dependencies(MyDependency) will make your package's ProjectConfig.cmake contain a find_package(MyDependency) call plus logic to combine CMake variables from MyDependency into your package's CMake variables. For example, it will make YourPackage_INCLUDE_DIRS contain everything in MyDependency_INCLUDE_DIRS. The purpose is so packages don't have to find your dependencies. Use ament_export_dependencies() on all dependencies of yours that downstream packages also need.
ament_export_interfaces() is a little different. This creates imported targets, which is a replacement for CMake standard variables in a ProjectConfig.cmake. It will likely be used more in the future, but for now there is at least one issue with it that needs to be fixed. It won't replace ament_export_dependencies(), but it will change how information like include directories and libraries are communicated between packages.
ROS Answers is licensed under Creative Commons Attribution 3.0 Content on this site is licensed under a Creative Commons Attribution Share Alike 3.0 license.
