how to write cmake with 1 executable and multiple subdirectories - c++

Question

I have a project with many sub-directories that each 1 of them include both header and source files. I want 1 executable which include all my src files.
I managed to write the cmake so it compiles successfully,
but Im dealing with 2 problems, I dont now how to solve:
1 - The compile time is very slow, probably somthing I'm doing wrong.
2 - I have few flags like DEBUG, RELEASE that I couldnt make it define/ undefine in any of the CMakeLists.txt files.
I need this because I have some of my source files :
#ifndef RELEASE /DEBUG #endif
My project stracture looks similar to this:
root/ (project root)
3rd_party/
spdlog/ ...
src/
CMakeLists.txt
main.cpp (contains main method)
logger/
log.c
logger.cpp
logger.hpp
CMakeLists.txt
first/
first_c.h
first.cpp
first.hpp
CMakeLists.txt
second/
second.cpp
second.hpp
CMakeLists.txt
control/
control.cpp
control.hpp
control_2.hpp
CMakeLists.txt
some more sub directories/...
build/
... (executable)
This is part from what I currently have :
in src/CMakeLists.txt:
cmake_minimum_required(VERSION 3.18)
project(integration LANGUAGES CXX)
set(src_main main.cpp)
add_subdirectory(first)
add_subdirectory(second)
add_subdirectory(third)
add_subdirectory(control)
add_subdirectory(logger)
add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/../3rd_party/spdlog ${CMAKE_CURRENT_BINARY_DIR}/spdlog)
set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)
add_executable(${PROJECT_NAME} ${src_main})
target_link_libraries(${PROJECT_NAME} control first second third logger)
target_compile_definitions(${PROJECT_NAME} PUBLIC RELEASE) # not working???
in src/control/CMakeLists.txt:
set(control_source_files
control.cpp
control.hpp
)
add_library(control SHARED ${control_source_files})
find_library(LIB paho-mqtt3c ${PROJECT_SOURCE_DIR}/lib)
set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)
target_link_libraries(control PUBLIC Threads::Threads)
target_link_libraries(control PUBLIC ${LIB})
target_include_directories(robot_control PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../second)
target_include_directories(robot_control PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../third)
in src/first/CMakeLists.txt:
set(first_source_files
first_c.h
first.cpp
first.hpp
)
add_library(first SHARED ${first_source_files})
target_include_directories(motor PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../second)
target_include_directories(motor PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../logger)
target_include_directories(motor PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../../3rd_party/date/include/)
Im not sure if I need target_include_directories I did it becuase in first.hpp there are icludes for headers in those subdirectories.
any help to do the compile time faster and define right the flags ??

Answer 1

1 - The compile time is very slow, probably somthing I'm doing wrong.
There might be many reasons.
Main cause is usually to many includes in header files. Froward declarations in as many places as possible of header files is very effective cure for that issue. There is even a tool which helps to clean up existing project Include What You Use (IWYU).
2 - I have few flags like DEBUG, RELEASE that I couldnt make it
define/ undefine in any of the CMakeLists.txt files. I need this
because I have some of my source files :
target_compile_definitions(${PROJECT_NAME} PUBLIC RELEASE) # not working???
You are doing that wrong. Depending on generator you use (if it supports multiple configuration or not), you can control this in configuration step or in build step, by passing extra parameters:
In case if generator do not have mtuple configurations you configure this this way:
cd build
cmake -DCMAKE_BUILD_TYPE=Debug ..
cmake --build .
See doc
If generator supports multiple configurations then:
cd build
cmake ..
cmake --build . --config Debug
target_include_directories(robot_control PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../second)
target_include_directories(robot_control PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../third)
This is wrong. target_include_directories defines which paths are important for given target (library). Now when something is PUBLIC then any target which will do target_link_libraries(someTarget PUBLIC sourceTarget) where sourceTarget is your library will be impacted by this path. someTarget will inherit include paths from public (or interface) of source target so you don't have to add them explicitly.
So basically this quted lines are obsolete (if second and third targets have this include paths defined as PUBLIC).