cmake undefined reference to function - cmake

Question

The project structure below is a simplified example. I tried to boil it down to the minimal amount of files to reproduce my issue.
.
├── CMakeLists.txt
├── subdir1
│   ├── CMakeLists.txt
│   └── subsubdir1
│   ├── CMakeLists.txt
│   ├── Example.cpp
│   └── Example.h
└── subdir2
├── CMakeLists.txt
├── main.cpp
└── subsubdir1
├── CMakeLists.txt
├── ExampleCreator.cpp
└── ExampleCreator.h
./CMakeLists.txt
cmake_minimum_required(VERSION 2.8)
project(test)
macro(add_sources)
file (RELATIVE_PATH _relPath "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}")
foreach (_src ${ARGN})
if (_relPath)
list (APPEND SRCS "${_relPath}/${_src}")
else()
list (APPEND SRCS "${_src}")
endif()
endforeach()
if (_relPath)
# propagate SRCS to parent directory
set (SRCS ${SRCS} PARENT_SCOPE)
endif()
endmacro()
add_subdirectory(subdir1)
add_subdirectory(subdir2)
add_executable(test ${SRCS})
subdir1/CMakeLists.txt
add_subdirectory(subsubdir1)
subdir1/subsubdir1/CMakeLists.txt
add_sources(Example.cpp)
subdir1/subsubdir1/Example.h
#ifndef EXAMPLE_H
#define EXAMPLE_H
class Example
{
public:
Example();
virtual ~Example();
};
#endif
subdir1/subsubdir1/Example.cpp
#include <stdio.h>
#include "Example.h"
Example::Example()
{
printf("Inside Example constructor\n");
}
Example::~Example()
{
}
subdir2/CMakeLists.txt
add_subdirectory(subsubdir1)
add_sources(main.cpp)
subdir2/main.cpp
#include "subsubdir1/ExampleCreator.h"
int main(int argc, char** argv)
{
ExampleCreator creator;
return 0;
}
subdir2/subsubdir1/CMakeLists.txt
add_sources(ExampleCreator.cpp)
subdir2/subsubdir1/ExampleCreator.h
#ifndef EXAMPLE_CREATOR_H
#define EXAMPLE_CREATOR_H
class ExampleCreator
{
public:
ExampleCreator();
virtual ~ExampleCreator();
};
#endif
subdir2/subsubdir1/ExampleCreator.cpp
#include "ExampleCreator.h"
#include "../../subdir1/subsubdir1/Example.h"
ExampleCreator::ExampleCreator()
{
Example* ex1 = new Example();
}
ExampleCreator::~ExampleCreator()
{
}
I'm hoping this is a really simple lack of understanding of how CMake handles dependencies. This compiles without error, but fails during linking. The make output below shows that Example.cpp isn't even compiling and I don't understand why.
user>:~/src/test/build$ make
Scanning dependencies of target test
[ 50%] Building CXX object CMakeFiles/test.dir/subdir2/subsubdir1/ExampleCreator.cpp.o
[100%] Building CXX object CMakeFiles/test.dir/subdir2/main.cpp.o
Linking CXX executable test
CMakeFiles/test.dir/subdir2/subsubdir1/ExampleCreator.cpp.o: In function `ExampleCreator::ExampleCreator()':
ExampleCreator.cpp:(.text+0x2b): undefined reference to `Example::Example()'
collect2: ld returned 1 exit status
make[2]: *** [test] Error 1
make[1]: *** [CMakeFiles/test.dir/all] Error 2
make: *** [all] Error 2
All the sources are appended to the SRCS variable in the root CMakeLists.txt file from what I can tell. So, why isn't Example.cpp getting compiled? or linked?

Answer 1

The directory subdir1 doesn't generate a binary. Add this:
project(Example)
add_library(Example Example.cpp)
instead of your add_sources. After this, you need to tell the project that uses it to link against it:
TARGET_LINK_LIBRARIES(subdir2 Example)
If your names differ, document yourself on the functionalities of these commands.