How can I link a library that contains conditional types/variables definition based on global variables defined through CMake?

Question

Introduction

I am trying to use Toulbar2 as a C++ library in my CMake project, however I am having much trouble linking it to my main executable.

I found many similar questions on this topic, both here and on other similar website, but none of them helped me with my specific issue. I tried literally everything and I did not menage to make it work, I was hoping that some of you may help me with that.

I am running Ubuntu 18.04, CMake version 3.23 and in my project I am using the standard C++11. I am a proficient programmer, but I am just an beginner/intermediate user of both C++ and CMake.

What I've already tried to do

I cannot list all my attempts, so I will only mention those I think are my best ones, to give you an idea of what I may be doing wrong.

1) In my first attempt, I tried to use the same approach I used for any non-standard library I imported, i.e. using find_package() in CMakeLists.txt to then link the found LIBRARIES and include the found INCLUDE_DIRS. However, I soon realised that Toulbar2 provides neither a Find<package>.cmake or <name>Config.cmake file. So, this approach could not work.

2) My second attempt is the one that in my opinion brought me the closest to the solution I hoped for. You can easily compile Toulbar2 as a dynamic library using the command: cmake -DLIBTB2=ON .. in an hypothetical build directory you previously created. After compiling with make you have your .so file in build/lib/Linux. After installation, you can make CMake find this library by itself using the command find_library. So, my CMakeLists.txt ended up looking like this:

[...]
find_library(TB2_LIBRARIES tb2)
if(TB2_LIBRARIES)
    set(all_depends ${all_depends} ${TB2_LIBRARIES})
else(TB2_LIBRARIES)
    add_compile_definitions("-DNO_TB2")
    message("Compiling without Toulbar2, if you want to use it, please install it first")
endif(TB2_LIBRARIES)
[...]
target_link_libraries(main ${all_depends})
[...]

This code works to some extent, meaning that CMake correctly finds the library and runs the linking command, however if I try to #include <toulbar2lib.hpp> the header is not found. So I figured out I should have told CMake where to find that header, so I ended up adding a

include_directories(/path/to/header/file's/directory)

However, I still have another problem. The header is found, but a lot of names used in the header are not found at compilation time. The reason is that in Toulbar2 some variables/types are defined conditionally by using preprocessing directives like #ifdef or #ifndef, and in turn the global variables used in these conditions are defined through CMake at compilation time. If you are interested in an example, I can mention the Cost type that is used in the mentioned header file. I see that there's a piece missing in the puzzle here, but I cannot figure out which one. Since I pre-compiled the library those definitions should exist when I include the header file, because I am correctly linking the correspondent library that contains those definitions.

3) My third attempt is less elegant than the the other two I mentioned, but I was desperately trying to find a solution. So, I copied the whole toulbar2 cloned folder inside my project and I tried to add it as a subdirectory, meaning that my main CMakeLists.txt contains the line:

add_subdirectory(toulbar2)

It provides a CMakeLists.txt too, there should be no problem in doing it. Then I include the src directory of toulbar2, that contains the header file I need, and I should be okay. Right? Wrong. I got the same problem that I had before with (2), i.e. some variables/types conditionally defined were not actually defined when I tried to compile my project, even though the subproject toulbar2 was correctly (no errors) compiled.

I just wanted to mention that any answer is welcome, however if you could help me figure out an elegant solution (see 1 or 2) for this problem it would be way better, as this code is intended to be published soon or later. Thank you in advance for your help.

Answer 1

Solution 2) looks fine. You just need to add the following compilation flags -DNDEBUG -DBOOST -DLONGDOUBLE_PROB -DLONGLONG_COST when compiling your project with toulbar2lib.hpp. See github/toulbar2 README.md how to compile without cmake for those flags (except WCSPFORMATONLY that should not by used in this context).