[CMake] CMake Linking Error

[buzz clay]

Hi,

I have not been able to find the answer to my current problem so I thought
I'd try a new post. Before diving into the details, please be aware that
the code I am writing compiles/runs perfectly with a personal Makefile I
wrote.

My code is written in C++ and has many different class definitions. To run
different simulations some classes may or may not have actual objects
created. However, there are other portions of the code that specifically
reference functions from nearly all classes (although this code might not
actually be used because the object was never created). The linking errors
that I am facing arise when I do not make an object of a given class. Other
parts of the code need to be aware that the class exists, even if an object
was never made. Although this seems like it would be a result of not
including the appropriate header files, I assure you they are correct! For
some reason, if I do not make an object of a given class cmake "ignores"
the class and when it comes time to link everything together I get the
following error:

Linking CXX executable collision
Output/libOutput.a(Output.cpp.o): In function
`Output::Output(std::vector<Ball*, std::allocator<Ball*> >*,
std::vector<CollisionObject*, std::allocator<CollisionObject*> >*)':
Output.cpp:(.text+0x379): undefined reference to `SWall::getY2()'
Output.cpp:(.text+0x391): undefined reference to `SWall::getX2()'
Output.cpp:(.text+0x3a9): undefined reference to `SWall::getY1()'
Output.cpp:(.text+0x3c1): undefined reference to `SWall::getX1()'
collect2: ld returned 1 exit status
make[2]: *** [collision] Error 1
make[1]: *** [CMakeFiles/collision.dir/all] Error 2
make: *** [all] Error 2

PLEASE NOTE: If in my main.cpp file I simply create an SWall object and
never use it, the errors go away and everything works perfectly. I simply
do not understand why cmake would care whether or not I actually make an
object of a given class!

The following is my CMakeLists.txt file in the highest level directory:

cmake_minimum_required(VERSION 2.8)

project(collision CXX)

add_subdirectory(Extraneous)
add_subdirectory(Output)
add_subdirectory(Simulation)
add_subdirectory(CollisionObject)

add_definitions(-ansi -Wall -O2)

add_executable(collision test.cpp)

target_link_libraries(collision Simulation)
target_link_libraries(collision PriorityQueue)
target_link_libraries(collision Event)
target_link_libraries(collision Ball)
target_link_libraries(collision SWall)
target_link_libraries(collision Circle)
target_link_libraries(collision Output)
target_link_libraries(collision SimpleMath)

INSTALL(PROGRAMS ${CMAKE_BINARY_DIR}/collision DESTINATION
${CMAKE_SOURCE_DIR})

All of the lower level directories simply had add_library(<libname>
<libname.cpp>) in the CMakeLists.txt file. Any help is greatly appreciated!

Thanks,
Matthew
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