Keeping file hierarchy across subdirectories in CMake

Question

Till date I still do not really understand what the \'best practice\' is for doing this for a CMake project with many subdirectories.

Say I have a project hierarchy

Answer 1

There is a fourth way if you're using newer versions of CMake.

Take a look at target_sources() command of CMake.

It seems like you are declaring your target in your CMakeLists.txt

add_executable(my_target "subd1/CMakeLists.txt" "subd2/CMakeLists.txt")
add_subdirectory(subd1)
add_subdirectory(subd2)

Instead of propagating your Source files up to the root you can depend on the target you have defined in the root CMakeLists.txt. That means subd1/CMakeLists.txt may look like:

target_sources(my_target PRIVATE "subd1/Source.cpp" "subd1/Source2.cpp")

[EDIT]

As stated in the comments you must give the relative path of the source-files to target_sources(). I use target_sources() because I do not want the explicit source file listing to pollute the targets CMakeLists.txt. Another use case is that target_sources() can be invoked with the PUBLIC or INTERFACE keyword to propagate source files to depending targets. Well I never used target_sources() that way.

[/EDIT]

If you're using IDEs like Visual Studio that support folders you make want to also declare a source_group() in the CMakeLists.txt that contains your target. So the root CMakeLists.txt may look like:

add_executable(my_target "subd1/CMakeLists.txt" "subd2/CMakeLists.txt")
add_subdirectory(subd1)
add_subdirectory(subd2)
...
source_group(subd1 REGULAR_EXPRESSION "subd1/*")
source_group(subd2 REGULAR_EXPRESSION "subd2/*")

I'm using this approach because it leads to much cleaner CMakeLists.txt files, its lesser work and I think the introduction of not needed variables only raises the complexity of your CMakeLists.txt files.

CMakeLists.txt as target sources

I currently use the CMakeLists.txt of the sub folders as source files of the target because otherwise CMake will complain that the add_executable command has no source files given.

Answer 2

In your case there's no need to use add_subdirectory since you have only one target which is created in the root CMakeLists.txt. You can simply write this:

add_executable(myProg
    SubD1/Source.cpp
    SubD1/SubSubD1/Source2.cpp)

Use add_subdirectory for subdirectories creating their own targets so there's no information to pass upwards.

Answer 3

There are 3 ways I have used before. I normally prefer the 1st way, but have already used all 3 depending on the use case:

1. You directly name the sources in your root CMakeLists.txt file

set(
    SUBD1_SOURCES
    "SubD1/SubSubD1/Source2.cpp"
    "SubD1/Source.cpp"
)

set(
    SUBD2_SOURCES
    "SubD2/Source3.cpp"
)

add_executable(myProg ${SUBD1_SOURCES} ${SUBD2_SOURCES})

2. You use OBJECT intermediate libraries to collect/group your sources

SubD1/SubSubD1/CMakeLists.txt:

add_library(SubSubD1Objs OBJECT Source2.cpp)

SubD1/CMakeLists.txt:

add_subdirectory(SubSubD1)
add_library(SubD1Objs OBJECT Source.cpp)

CMakeLists.txt:

add_executable(myProg $<TARGET_OBJECTS:SubSubD1Objs> $<TARGET_OBJECTS:SubD1Objs>)

3. You write your own function() to collect the data (and do the prefixing)

CMakeLists.txt:

function(my_collect_sources)
    foreach(_source IN ITEMS ${ARGN})
        if (IS_ABSOLUTE "${_source}")
            set(source_abs "${_source}")
        else()
            get_filename_component(_source_abs "${_source}" ABSOLUTE)
        endif()
        set_property(GLOBAL APPEND PROPERTY GlobalSourceList "${_source_abs}")
    endforeach()
endfunction(my_collect_sources)

add_subdirectory(SubD1)
#add_subdirectory(SubD2)

get_property(MY_SOURCES GLOBAL PROPERTY GlobalSourceList)
add_executable(myProg ${MY_SOURCES})

SubD1/CMakeLists.txt:

add_subdirectory(SubSubD1)
my_collect_sources(Source.cpp)

SubD1/SubSubD1/CMakeLists.txt:

my_collect_sources(Source2.cpp)