How to include header file from different workspace?

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Hey, I am new to ROS and its my first post, so I hope everything is understandable.

I am trying to include a header file in the package (B) from a different package (A) which is in a different workspace. I can include messages from the package. I overlayed the workspace and added the the packge in the CMakeLsts.txt

find_package(catkin REQUIRED COMPONENTS
A
)

catkin_package(
CATKIN_DEPENDS
A
)

install (DIRECTORY include/${A}/
DESTINATION ${CATKIN_PACKAGE_INCLUDE_DESTINATION}
FILES_MATCHING PATTERN "*.h")

add_library(library A/src/AClass.cpp)

add_executable(ClassIncludeAClass  src/ClassIncludeAClass.cpp)
target_link_libraries(ClassIncludeAClass   ${catkin_LIBRARIES} library )

ClassIncludeAClass .cpp

#include "A/AClass.h"

When I include the whole path to the file the Compiler has undefined references to functions of the class AClass.

I found the following question https://answers.ros.org/question/2019... to include a header form the same Workspace but a different package.

Thanks in advance for any help!