assuming I have 2 cmake modules
MyStaticLib which is after compilation will be a static library
Connector which is a shared lib or executable, and it's should use MyStaticLib inside.
So, I want to add MyStaticLib inside Connector but not simply put myStaticLib.a + headers in some folder, but reference MyStaticLib module from Connector, so when Connector compile it will build lib from sources and use it.
What is a proper way to do that in cmake?
In case of independent projects (MyStaticLib is used by other projects to, has it's own release cycle), you can use:
find_library:
Build, test and install MyStaticLib into your file system
add find_library into Connector's CMakeList.txt
find_package
Similary to above but MyStaticLib provides additional information
ExternalProject
In case you want to trigger any additional actions (build, patch) on MyStaticLib before usage by Connector
Gives you the most possibilities
In case of dependent projects (MyStaticLib is a subproject of Connector), just add it as subdirectory of Connector (It must be a subdirectory).
Related
I have a program that depends on an external library (SDL for example). I want CMake to take care of that dependency for me, so I was looking into FetchContent. As far as I understand, this module simply downloads the source code so that information on the external library is available at configure time. For example:
include(FetchContent)
FetchContent_Declare(sdl
GIT_REPOSITORY <...>
)
FetchContent_GetProperties(sdl)
# sdl_POPULATED, sdl_SOURCE_DIR and sdl_BINARY_DIR are ready now
if(NOT sdl_POPULATED)
FetchContent_Populate(sdl)
endif()
At some point, however, I want to build that source code and link it to my main executable. How to do it the "modern CMake way"?
The recommended way to build external libraries from source as part of your build depends on what the external lib provides build-wise.
External lib builds with cmake
If the external lib builds with cmake then you could add the lib to your build via a add_subdirectory(${libname_SOURCE_DIR}) call. That way cmake will build the external lib as a subfolder ("subproject"). The CMakeLists.txt file of the external lib will have some add_library(ext_lib_name ...) statements in it. In order to then use the external lib in your targets (an application or library that depends on the external lib) you can simply call target_link_libraries(your_application <PRIVATE|PUBLIC|INTERFACE> ext_lib_name) https://cmake.org/cmake/help/latest/command/target_link_libraries.html
I had a quick look at this github repo https://github.com/rantoniello/sdl - (let me know if you are referring to another library) and it actually looks like it is building with cmake and that it allows clients to statically or dynamically link against it: https://github.com/rantoniello/sdl/blob/master/CMakeLists.txt#L1688-L1740
So, ideally your applicaiton should be able to do
add_executable(myapp ...)
target_link_libraries(myapp PRIVATE SDL2-static) // Statically link againt SDL2
Due to their CMakeLists.txt file the SDL2-static comes with properties (include directories, linker flags/commands) that will automatically propergate to myapp.
External lib does not build with cmake
If a external lib doesn't build with cmake then one can try to use add_custom_target https://cmake.org/cmake/help/latest/command/add_custom_target.html to build the library. Something along the lines of:
add_custom_target(myExternalTarget COMMAND <invoke the repo's build system>)
You'd then need to set the target properties that are important for clients yourself via the the proper cmake functions set_target_properties, target_include_directories ... A great writeup how to get started with these kinds of things: https://pabloariasal.github.io/2018/02/19/its-time-to-do-cmake-right/
I want to build two projects using cmake (A library and sandbox application using that library).
I'm currently having the following folder structure:
-- yanthra_engine
|
-- CMakeLists.txt
-- lib
-- ...
-- sandbox
|
-- CMakeLists.txt
-- out
-- ...
The yantra_engine builds a library where as sandbox builds an executable(using the above mentioned library).
Should I keep full fledged CMakeLists files for both the projects? Is there any efficient folder structure to follow?
I would like the library to build automatically when building my sandbox application, but not vice-versa.
You should keep seperate CMakeLists.txt files. It's good practice to use one CMakeLists.txt file per unrelated target. (Unrelated in the sense of not being different builds of the same library, e.g. one shared one static.)
Whether to add both targets to the same project is basically up to you. If the library is properly set up, you could create a seperate project for the library and use it's install target to install the library including cmake configuration files on your machine making it easy to import the installed library as a target to the sandbox project. This requires you to add the appropriate install commands to the library.
If you want to be able to build both the library and the sandbox via the same build files, basically all you need to do is to make sure both CMakeLists.txt files are reachable from a CMakeLists.txt file.
Without location of any of the files you could e.g.
Create a CMakeLists.txt file in the parent folder adding both subdirectories
cmake_minimum_required(VERSION 3.0)
project(CommonProject)
add_subdirectory(yanthra_engine)
add_subdirectory(sandbox EXCLUDE_FROM_ALL) # targets in sandbox not built by default.
You could also include the yanthra_engine directory from sandbox/CMakeLists.txt
...
add_subdirectory(../yanthra_engine "${CMAKE_BINARY_DIR}/yanthra_engine_build")
...
Both approaches allow you to either set up a build project for the lib on its own or set up a build project for both. In approach 1 the source directory for building both would be the parent directory of yanthra_engine and sandbox and in approach 2 it would be sandbox.
For both approaches you don't need to wory about unnecessarily building the sandbox project though as long as you specify the target you want to build. Since sandbox links the lib but there is no dependnecy established the other way round building sandbox makes sure the lib is up to date, but building the lib only builds the lib and its dependencies which excludes the sandbox.
One thing you can try is to let yanthra be a subdirectory of sandbox. Then you can do this in sandbox:
add_subdirectory(yanthra_engine)
I am using a third party macOS framework called CrashReporter in my CMake project like so:
cmake_minimum_required(VERSION 3.15)
set(CMAKE_OSX_DEPLOYMENT_TARGET "10.9" CACHE STRING "Minimum OS X deployment version")
project(bug CXX)
find_package(CrashReporter REQUIRED)
add_executable(bug
"${CMAKE_CURRENT_SOURCE_DIR}/main.mm"
)
set_target_properties(bug PROPERTIES LINK_FLAGS "-ObjC")
target_link_libraries(bug PUBLIC "-framework AppKit")
target_link_libraries(bug PRIVATE ${CRASHREPORTER_FRAMEWORK})
If I copy my executable to another machine it complains that the library is not found.
Is it possible to statically link (not embed) the framework in the executable?
A Framework and a static library are two different things. You can't change the nature of a framework to it to be statically linked. BUT! Your third party provider may offer you an installation package that includes a framework, a dynamic library and a static library, so you may have the option to choose the one to link. Or if your third party library is open source you can build it yourself as you prefer. It is even possible that the static and dynamic libraries are shipped inside the framework, because a framework is symply a directory similar to an app bundle. If you installed a package with several flavors, then you may set this variable to influence the find_package results:
CMAKE_FIND_FRAMEWORK(NEVER)
Before find_package() so CMake will ignore frameworks and search only for unix libraries.
If you know that there is a static library, and where it is, you may provide the full name of the static library to the target_link_libraries() command:
target_link_libraries(bug PRIVATE ${CRASHREPORTER_STATIC_LIBRARY})
Assuming that there is a CRASHREPORTER_STATIC_LIBRARY variable holding the full name and path of the static library (something like '/path/to/crashreporting.a').
I am trying to build a program using CMake that depends on a third party library. This third party library contains a CMakeLists.txt file so what I want to do is keep the source code of the third party library within my project directory, and build it using add_subdirectory(path/to/lib), and then link my target against the static library that the third party library generated.
my CMakeLists.txt:
cmake_minimum_version(VERSION 3.10)
project(my_project)
add_subdirectory("${CMAKE_SOURCE_DIR}/extern/somelib")
# my-code:
# somelib CMakeLists.txt file has a project name: SOMELIB
# which lets me access the directory where the files are built
# on windows it builds to /Release, on mac and linux it just builds
# to the binary dir
set(SOMELIB_LIBS "${SOMELIB_BINARY_DIR}/Release")
add_executable(my_program my_main.cpp)
target_link_libraries(my_program "${SOMELIB_LIBS}/SOMELIB.lib" "${SOMELIB_LIBS}/SOMELIBmain.lib")
I then make a build directory and from that directory I do:
cmake -G "Visual Studio 15 2017" ..
cmake --build .
The build command fails with a "LINK : fatal error LNK1181: cannot open input file 'extern/somelib/Release/SOMELIBmain.lib' ..."
My workaround for now has been to comment out the part that says "#my-code", build the somelib dependency first which generates the static libraries, and then uncomment out my-code and build again which then works correctly.
How can I tell CMake to build the subdirectory first, and then link against the static libraries that it generated?
Short answer: tell CMake that there is dependency between its targets.
target_link_libraries(my_program PRIVATE SOMELIB SOMELIBmain)
CMake will evaluate SOMELIBs locations for you and link my_program against SOMELIB and SOMELIBmain[1]. Works for both Debug and Release configurations and also for Linux.
You shouldn't have to worry where CMake places build files[2] and this is what so called "modern CMake" is trying to achieve. I will leave here just brief description but check link on the bottom of answer[3].
Anyway, the key concept is that whenever you create library/executable (target), you list its usage+build requirements and dependencies to other targets. You declare dependencies using target_link_libraries(<your_lib> KEYWORD <dependencies>). Such line will not only make <you_lib> link against listed dependencies, it will inherit their usage requirements (usually, public include directories) and order CMake to build dependent libraries before <your_lib>.
The beauty of it is that even if SOMELIB does not follow modern CMake ideas (does not declare build/usage requirements), you still should be able to do just with this single line.
[1] I assumed that CMake targets are named same as output library names, but it is not mandatory. For OP's case it turned out that static library targets are suffixed with -static, so he had to write SOMELIB-static SOMELIBmain-static
[2] Unfortunately, it is not so easy with shared libraries on Windows (DLLs)
[3] I'd start with this blog entry: https://pabloariasal.github.io/2018/02/19/its-time-to-do-cmake-right/
I have the following situation:
I'm working on an application that depends on a number of third party libs, among them wxwidgets
I build the application for multiple target configurations (x86, arm, Linux, Windows) using Linux as my build host system
Due to the above mentioned multiple target configurations, I have chosen to build those third-party libs from source, using CMake's ExternalProject_Add function.
The third-party libs are built 'on-demand' at a location separate from my application's CMAKE_BINARY_DIR so that I can wipe the build tree for my application without having to rebuild the third-party libs (takes a looooong time).
The location of the third-party libs is different depending on what target configuration I build them for (obviously).
I'm quite new to CMake and the problem I currently face is this:
The source files in my application can't find the wx include files and I need to set the correct linker flags to be able to link my application against wxwidgets.
This seems to be handled by a utility 'wx-config' that provides exactly that info as output when run with either the --cppflags or --libs flag. I can not however, figure out how to catch that output and append it to the include dirs and linked libraries I setup from my CMakeLists.txt files.
So basically what I want is.
Build wxwidgets (if it doesn't exist) for the current target configuration
Run wx-config --cppflags and --libs to find out the correct include dirs and linker flags for the current target configuration
Use the info from step 2 when building targets that are my own application
So far I've tried something like this:
# Set a target-configuration-specific location
set(wxwidgetsTop ${MYPROJECT_EXTERNAL_DIR}/wxwidgets/wxwidgets_${MYPROJECT_CURRENT_TARGET_CFG})
# Build the project
ExternalProject_Add( wxWidgetsExternal
PREFIX ${wxwidgetsTop}
URL ${MYPROJECT_EXTERNAL_DIR}/tarballs/wxWidgets-3.0.2.tar.bz2
SOURCE_DIR ${wxwidgetsTop}/src/wxwidgets
CONFIGURE_COMMAND ${configure_cmdline}
BUILD_COMMAND make -j${MYPROJECT_NCPU}
INSTALL_COMMAND make install
)
# Create a wxwidgets target to be used as a dependency from other code
add_library(wxWidgets IMPORTED STATIC GLOBAL)
add_dependencies(wxWidgets wxWidgetsExternal)
# (non-working) attempt to get the correct include dirs and linker
# flags for wxwidgets
add_custom_command(TARGET wxWidgetsExternal
POST_BUILD
COMMAND ${INSTALL_DIR}/bin/wx-config ARGS --cppflags
COMMENT "Running wx-config"
)
but the above does not provide a way to actually use the result from the custom command to append the cppflags and linker options when building the targets that make up my application.
What is a good way to achieve what I want?
I see three different ways of doing this:
Method 1: use find_package
Use wxWidgets as a standalone requirement for your project, and expect the devs to install it before building your project. In your CMakeLists.txt you will need to call find_package(wxWidgets), like this:
find_package(wxWidgets COMPONENTS net gl core base)
if(wxWidgets_FOUND)
include(${wxWidgets_USE_FILE})
# and for each of your dependent executable/library targets:
target_link_libraries(<YourTarget> ${wxWidgets_LIBRARIES})
endif()
This has the advantage of not rebuilding the lib if you rebuild your project, however it requires some work for your user (they need to handle the installation of wxWidgets by hand) and for you (you need to setup include paths / compile definitions / ... by hand).
Method 2: embed wxWidgets
The second option is to bundle wxWidgets in your repo (svn external or git submodule) and usually (re)write the CMakeLists.txt of this lib to be target-oriented. Then, in your top-most CMakeLists.txt, you can do the following:
# for example, if you just need core and net:
target_link_librairies(my_app PUBLIC wxWidgetsCore wxWidgetsNet)
# No need to manually setup include dirs, etc...
To make a CMakeLists.txt target-oriented, you define include directories and other compilation properties for a target, not a directory. Example:
# When defining wxWidgetsCore, for example
add_library(wxWidgetsCore ...)
target_include_directories(wxWidgetsCore PUBLIC someDir)
target_compile_definitions(wxWidgetsCore PUBLIC -pedantic)
target_link_libraries(wxWidgetsCore PUBLIC someLib)
The drawback of this approach is that rebuilding your project will trigger a rebuild of wxWidgets. However, it is possible to trick this by not using "rebuild" but "clean just my app, then build". Here is some insight on how to achieve this.
Method 3: some sort of hybrid
The big drawback of method 2 leads to the third approach: don't put wxWidgets in your project, but create a CMakeLists.txt that will "import" the lib. The idea: you ask your user for the directory where wxWidgets is installed, then this script will setup everything for your project. First, put the CMakeLists.txt here:
/your-project-root
/thirdparty
/wxWidgets
CMakeLists.txt
/dir-where-wxwidgets-is-installed
...
Now, you define an imported target:
# When defining wxWidgetsCore, for example
set(WX_INCLUDE_DIR ${USER_SPECIFIED_WX_ROOT}/include)
add_library(wxWidgetsCore IMPORTED GLOBAL)
set_property(TARGET wxWidgetsCore APPEND PROPERTY
INTERFACE_INCLUDE_DIRECTORIES ${WX_INCLUDE_DIR})
See INTERFACE_INCLUDE_DIRECTORIES and INTERFACE_LINK_LIBRARIES. You need your user to have build wxWidgets somewhere in his system, but from your point of view you just do target_link_libraries(your_app PUBLIC wxWidgets...), as in method 2. The advantage is that this approach is interchangeable with method 2 transparently, and you don't put the whole dependency in your project.
Setting cppflags and linker flags has to be done at CMake time, but you are trying to run wx-config at build time and you are not capturing its output anyway, so your add_custom_command() isn't doing anything useful other than printing things to the build tool's output.
Ideally, you would use the FindwxWidgets module CMake already provides. It requires wxWidgets to already be built (but see further below). Have a look at the CMake documentation for it and see if that at least sounds like what you are trying to achieve manually by using wx-config. If you can get FindwxWidgets to do the job for you, that would be a much cleaner approach.
Getting something to build at configure time so you can use it later on in your CMakeLists.txt file is a bit more tricky. ExternalProject_Add() downloads and builds things at build time, but you need wxWidgets to be built earlier at configure time. I wrote an article recently for how to do at least the downloading part at configure time and you should be able to adapt it to do the whole build at configure time instead. The article uses Google Test as its example and can be found here:
https://crascit.com/2015/07/25/cmake-gtest/
It would be trivial to make it put the wxWidgets build wherever you like, not just in the CMAKE_BINARY_DIR area. That would allow you to have different wxWidgets builds for each build configuration and to be able to wipe out your application's build tree independently of the wxWidgets builds.
Hope that points you in the right direction.
The solution I use checks for wxWidgets installation in the system using find_package, if it's not found, then the script downloads wxWidgets from github and links the program against downloaded library. The lib is installed in the build directory, so only the first build is slow - subsequent builds do not even check wxWidgets sources timestamps, so the process is as fast as building using preinstalled wxWidgets library.
Here's how my script does it:
It quietly checks for wxWidgets installation using find_package(wxWidgets QUIET),
If it's found, the script adds a dummy library wxWidgets_external,
If it's not, then it creates an ExternalProject named wxWidgets_external which downloads, builds and installs the library in the build dir, setting wxWidgets_ROOT_DIR to point to the wxWidgets installation dir,
Then we add another ExternalProject pointing to a folder with the main program's source files and CMakeLists.txt build script. This external projects depends on wxWidgets_external which is either a dummy library in case wxWidgets is preinstalled in the system, or an external project set up to download the library from github,
In the aforementioned CMakeLists.txt we again call find_package, this time with REQUIRED parameter and use the library the standard way (https://docs.wxwidgets.org/trunk/overview_cmake.html). Because we set up the dependencies and variables correctly, this call will use either preinstalled wxWidgets (if it's available) or the one downloaded from github.
There are more quirks to it, but that's the gist of it. The full sample code (tested on Linux, Windows and Mac) is available on github (https://github.com/lszl84/wx_cmake_template).
Also see full blog post which explains this in more detail: https://justdevtutorials.medium.com/wxwidgets-cmake-multiplatform-superbuild-4ea86c4e6eda