Is there any way to create a FindXXX.cmake automatically where XXX is my Cmake project? I see many projects that they created their FindXXX.cmake manually but I believe it's possible to create it automatically.
And, where I should install my project on Linux?
Thanks!
Take a look at CMake's project config file mechanism (along with the CMakePackageConfigHelper module; you might also want to take a look at this wiki page).
Find scripts are most useful for locating dependencies that are not aware of CMake themselves. If on the other hand the dependency was also built using CMake, you can let CMake auto-generate a project config file for you as part of that project's build process. This config file will allow you to refer to the targets of that project from an enclosing project as if they were being built as part of the enclosing project's CMake run. This is even more powerful than using find scripts, as it allows for example distinct handling of configurations beyond the debug/optimized options available to traditional find scripts.
On Windows, projects generating config files this way will register themselves with CMake, so that depending projects building on the same machine can find them automatically without any additional configuration. If you are building on non-Windows platforms (or you are building the two libraries on different machines) you will have to place the config file in a default directory (the docs for find_package describe which directories are searched) or explicitly point CMake to the location using CMAKE_MODULE_PATH.
Modern CMake-aware libraries should always prefer this approach over traditional find scripts. A prominent example of a library that does this already is Qt5.
CMake supports templating with configure_file() command.
Standard dirs where CMake searches for FindXXX.cmake modules are listed in the documentation of find_package() command.
Related
I'm working on a project with a lot of external dependencies, which are included in the project tree. I would like to pre-build all of the dependencies and share the importable targets within the project tree.
I was planning to use cmake install with a CMAKE_INSTALL_PREFIX in the source tree, and use CMAKE_PREFIX_PATH to reference it for find_package. However, I'm beginning to wonder how maintainable this strategy is going to be? For example here's something I noticed in one of the installed cmake scripts:
${CMAKE_PREFIX_PATH}/lib/cmake/glfw3/glfw3Targets.cmake:
set_target_properties(glfw PROPERTIES
INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
INTERFACE_LINK_LIBRARIES "/usr/lib/x86_64-linux-gnu/librt.so;/usr/lib/x86_64-linux-gnu/libm.so;dl;/usr/lib/x86_64-linux-gnu/libX11.so;-lpthread"
)
It seems really suspicious to me that all of those link libraries are fully resolved to paths on the host machine.
I guess the question is: Are cmake installs to a prefix meant to be distributable and this is just a bad example, or are they meant to be tied to the machine you "install" them on? Ie. Is prefix really meant to just relocate where on the system things are supposed to be "installed", and my hope to use it as a shared package manager likely to be problematic?
Yes, EXPORT'ed CMake targets can be "distributable", but the project should follow some principles for achieve that.
If you link with a (external) library, but do not want export file to contain absolute path to it, then do not pass absolute path directly to target_link_libraries.
In case a linked library is shipped with a compiler (e.g. m or rt), things are simple: just pass the library's name to the target_link_libraries.
In case a linked library YYY comes from other package and is detected by find_package(YYY), this implies several things:
Script FindYYY.cmake or YYYConfig.cmake should return IMPORTED target. If this is not true, you may try to wrap its results into IMPORTED target.
target_link_libraries should use this IMPORTED target.
Script XXXConfig.cmake, shipped with your project, should use find_dependency(YYY) for discover a library on a user machine.
For find_dependency(YYY) work, a user machine should have FindYYY.cmake or YYYConfig.cmake script. Alternatively, you may ship FindYYY.cmake with your project, and adjust CMAKE_MODULE_PATH variable before find_dependency() call (in your XXXConfig.cmake).
I'm creating a very small project that depends on the following library: https://github.com/CopernicaMarketingSoftware/AMQP-CPP
I'm doing what i always do with third-party libraries: i add their git repo as a submodule, and build them along with my code:
option(COOL_LIBRARY_OPTION ON)
add_subdirectory(deps/cool-library)
include_directories(deps/cool-library/include)
target_link_libraries(${PROJECT_NAME} coollib)
This has worked perfectly for libraries like Bullet, GLFW and others. However, this AMQP library does quite an ugly hack. Their include directory is called include, but in their CMake install() command, they rename it to amqpcpp. And their main header, deps/cool-library/amqpcpp.h, is referencing all other headers using that "fake" directory.
What happens is: when CMake tries to compile my sources which depend on deps/cool-library/amqpcpp.h, it fails because it's not finding deps/cool-library/amqpcpp/*.h, only deps/cool-library/include.
Does anyone have any idea how i can fix this without having to bundle the library into my codebase?
This is not how CMake is supposed to work.
CMake usually builds an entire distributive package of a library once and then installs it to some prefix path. It is then accessible for every other build process on the system by saying "find_package()". This command finds the installed distibution, and all the libs, includes etc. automagically. Whatever weird stuff library implementers did, the resulting distros are more or less alike.
So, in this case you do a lot of unnecessary work by adding includes manually. As you see it can also be unreliable.
What you can do is:
to still have all the dependencies source distributions in submodules (usually people don't bother doing this though)
build and install each dependency package into another (.gitignored) folder within the project or outside by using their own CMakeLists.txt. Let's say with a custom build step in your CMakeLists.txt
use "find_package()" in your CMakeLists.txt when build your application
Two small addition to Drop's answer: If the library set up their install routines correctly, you can use find_package directly on the library's binary tree, skipping the install step. This is mostly useful when you make changes to both the library and the dependent project, as you don't have to run the INSTALL target everytime to make library changes available downstream.
Also, check out the ExternalProject module of CMake which is very convenient for having external dependencies being built automatically as part of your project. The general idea is that you still pull in the library's source as a submodule, but instead of using add_subdirectory to pull the source into your project, you use ExternalProject_Add to build it on its own and then just link against it from your project.
I have a CMAKE project that depends on other projects built with CMAKE. These are : glfw, oglplus, portaudio etc.
How should I set up my project to work well in a cross platform fashion? What is the recommended way to go about it? I have been trying to read the CMAKE documentation but could only find examples to simple scenarios.
Just add the dependencies to your project README and expect the user stored them (already compiled) in system scope.
Add CMake options to request the path to dependency files.
Use add_subdirectory to chain your project with dependencies.
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
Say I am creating a project that uses a certain library and I have to provide the path for that library while linking. In the command line or makefile I might have:
g++ ... -L/path/to/mylibrary
I'm also going to send this project to someone else who wants to use it. The path on their system might not necessarily be the same as mine. They could be using a different file path all together.
How do I make sure that the path to the library works for both my computer and the recipient of my project?
This is the role of a build system or build configuration tool. There are many of those around. The main one is probably CMake as it has a very extensive feature set, cross-platform, and widely adopted. There are others like Boost.Jam, autoconf, and others.
The way that these tools will be used is that they have automated scripts for looking into the file-system and finding the headers or libraries that you need, i.e., the dependencies required to compile your code. They can also be used to do all sorts of other fancy things, like checking what features the OS supports and reconfiguring the build as a consequence of that. But the point is, you don't hard-code any file-paths into the build configuration, everything is either relative to your source folder or it is found automatically by the build script.
Here is an example CMake file for a project that uses Boost:
cmake_minimum_required (VERSION 2.8)
project (ExampleWithBoost)
find_package(Boost 1.46 COMPONENTS thread program_options filesystem REQUIRED)
# Add the boost directory to the include paths:
include_directories(SYSTEM ${Boost_INCLUDE_DIR})
# Add the boost library directory to the link paths:
link_directories(${Boost_LIBRARY_DIRS})
# Add an executable target (for compilation):
add_executable(example_with_boost example_with_boost.cpp)
# Add boost libraries to the linking on the target:
target_link_libraries(example_with_boost ${Boost_LIBRARIES})
The find_package cmake function is simply a special script (specialized for Boost, and installed with CMake) that finds the latest version of boost (with some minimal version) installed on the system, and it does so based on the file-name patterns that the library uses. You can also write your own equivalents of find_package, or even your own package finders, using the functions that CMake provides for searching the file system for certain file-name patterns (e.g., regular expressions).
As you see, the build configuration file above only refer directly to your source files, like "example_with_boost.cpp", and it's only relative to the source folder. If you do things right, the configuration scripts will work on virtually any system and any OS that CMake supports (and that the libraries you depend on support). This is how most major cross-platform projects work, and when you understand how to work with these systems, it's very powerful and very easy to use (in general, far easier to use and trouble-free than build configurations that you do by point-and-click within IDE menus like in Visual Studio).
You can use premake that generates cross platform makefiles: Visual Studio, Gcc and others
http://industriousone.com/what-premake
CMake is another alternative
http://www.cmake.org/
I'm not sure if there's a single universal way of doing this, but people often provide different config files and let the main Makefile detect which one to include: linux.make, darwin.make, cygwin.make etc.
there are also various tools like CMake that allow to automate this, but all in all it's just scripting that hides the system-dependency from the developer.