CMake + find package or check out and install - c++

I just switched to CMake. And yet found it very useful and realized some simple apps and libs.
Somewhere I read that it's possible to query git to checkout repositories from within cmake scripts.
I'd like to check for the existence of a package with my Find(package).cmake
If it doesn't exist i'd like to initiate a checkout and add the new directory to the cmake script as subdirectory.
That way all my dependencies will get installed automatically.
Does somebody know how to accomplish this idea? Thank you!
Bye, Arthur

You're probably thinking about the ExternalProject module added in CMake 2.8. It's documented at http://www.cmake.org/cmake/help/cmake-2-8-docs.html#module:ExternalProject with an intro to it at page 14 of http://www.kitware.com/products/archive/kitware_quarterly1009.pdf. It allows you checkout/download a project and build it automatically.

I would try to find the package with find_package and if the package_FOUND variable is not set you have to call git manually with execute_process. If the source already contains a CMakeLists.txt simply add it by using add_subdirectory otherwise you have to write your own CMake instructions to build that package first.

Related

CMake - Install Find script for depencency together with script

I am making a CMake library around some installable SDK. So the dependency tree looks like:
Application --> MyLibrary --> OfficialSDK
This SDK is installed by some setup.exe and does not have a CMake module.
So instead I include a custom find script inside MyLibrary: MyLibrary/cmake/FindOfficialSDK.cmake. Then inside the CMakeLists.txt of MyLibrary I can use find_package(OfficialSDK).
This works well for MyLibrary. I can build it and install it, together with the CMake export. So then Application can run find_package(MyLibrary) out of the box, since MyLibrary was installed properly using CMake.
However, when configuring Application I get an error:
Target "Application" links to target "OfficialSDK" but the target was not found.
Okay, so MyLibrary remembers it needs OfficialSDK, but it cannot find it in this CMake project.
I could solve this by including cmake/FindOfficialSDK.cmake in Application, but I would rather not make my users to copy the find script in case I need to update it in the future.
Is there some way of including the imported target OfficialSDK and install it together with MyLibrary, so Application doesn't need to search for it?
I found a solution, largely based on https://discourse.cmake.org/t/install-findpackage-script/5307.
Another example I found inside Pagmo2, for a custom FindBoost script: https://github.com/esa/pagmo2/blob/master/pagmo-config.cmake.in#L10
In a nutshell, I've added the following:
Added an install for my custom find script: install(FILE ${CMAKE_CURRENT_DIR}/cmake/FindOfficialSDK ...)
Added a custom *-config.cmake.in script that will be installed, aside from the more automatic *-targets.cmake export
Added an explicit find_dependency(OfficialSDK) (not find_package) inside this config script, but inside a clause that adds the MyLibrary cmake install directory to the CMake module path, so the custom find script is used.
A complete example can be seen this PR: https://github.com/ET-BE/AdsClient/pull/1/files (as well as a bunch of other stuff). The OfficialSDK is TwinCAT's ADS library.

Install IPOPT locally into C++ codebase with CMake ExternalProject

I would like to use Ipopt in a CMake-based project using ExternalProject. The library should be installed locally and automatically in the build folder so that the user must not go through any hassle.
I can do this for simple enough repositories that do not have many dependencies; unfortunately, this is not the case for Ipopt, whose installation requires a set of packages to be installed first.
How can install and use Ipopt in a local, self-contained way using CMake ExternalProject? If this cannot be done, is there an approach that would make the process at least partially self-contained? I would be very grateful for any answer with a working CMake script!

Install eigen3.3.7 on MacOS

I am trying to build a program on MacOS and that program requires Eigen version <= 3.3.7 but mine has 3.3.8 with brew install eigen
I went to Eigen website but 3.3.7 source is no longer available anymore.
Any workaround?
Thanks a lot!
Updates: thanks a lot but I am still very confused with how to proceed. Below is the information of the installation details and directory info.
The directory of the program source code that I want to build look like:
program
cmake
Cmakelist.txt
build
the program has the following instructions:
Create the build directory in the source tree root
mkdir build
Configure cmake, from the build directory, passing the Shogun source root as an argument. It is recommended to use any of CMake GUIs (e.g. replace cmake .. with ccmake ..), in particular, if you feel unsure about possible parameters and configurations. Note that all cmake options read as -DOPTION=VALUE.
cd build
cmake [options] ..
Compile
make
Install (prepend sudo if installing system-wide), and you are done.
make install
Sometimes you might need to clean up your build (e.g. in case of some major changes). First, try
make clean
Then I have downloaded eigen3.3.7, where the INSTALL file is as following. How should I proceed?
Method 1. Installing without using CMake
****************************************
You can use right away the headers in the Eigen/ subdirectory. In order
to install, just copy this Eigen/ subdirectory to your favorite location.
If you also want the unsupported features, copy the unsupported/
subdirectory too.
Method 2. Installing using CMake
********************************
Let's call this directory 'source_dir' (where this INSTALL file is).
Before starting, create another directory which we will call 'build_dir'.
Do:
cd build_dir
cmake source_dir
make install
You can install Eigen 3.3.7 by compiling the source code(available here).

Does CMake has a "find-or-download-and-run-build-command" mechanism?

CMake has a find_package() backed by a bunch of FindXYZ scripts (which you can also add to).
What mechanism, if any, is available to me to tell cmake: "Find this package, and if you haven't found it, download it and trigger its build" - with the downloading and building part also backed by per-package scripts or settings (so that downloading could be with wget or git clone, building could be with cmake or maven or a package-specific command, etc.) ?
Yeah, I was bitten by that Friday.
So, CMake has an ExternalProject directive, meant for exactly that, get/update if necessary, configure, build and install this and that external project. Awesome!
Sadly, CMake isn't that awesome.
You can't use the target defined by ExternalProject as a library in target_link_libraries. I've really tried to.
The basic problem is that the updating, building and installation of the external project happens at build time, whereas CMake insists on only using libraries that it found during pre-build (i.e. during the CMake run); you can't re-detect stuff while running make/ninja/msvc… .
You can define a custom target, tell it where the .so you'd want to link against later will be, and try to coerce CMake into believing you without checking at pre-build. Sadly, at least in the CMake versions I had, that broke dependency tracking, so that it simply didn't build the external library, because nothing needed it.
From the error messages you get when trying to use an external project in target_link_library, it seems CMake assumes you'd only want to install tools you need at build time that way, not libraries. A bummer.
You can roll your own version of download-on-demand using execute_process() (which runs on the CMake configure step) with ${CMAKE_COMMAND} as the command invoked on a CMakeLists.txt containing ExternalProject_Add().
You could even either configure_file() the CMakeLists.txt to fill out custom variables or dynamically create the CMakeLists.txt file.

Using CMake to find dependencies in an application-specific subfolder

In spite of many years of coding large-scale C++ applications, I do not understand how find_package is supposed to work in a medium-size CMake project, ASSUMING that I want to build the source to dependent packages myself and not simply rely on large systems like opencv, pcl or boost being installed somewhere in a system folder. I can't can't believe that I'm the only person in the world who has shipped multiple OpenCV and other open-source apps, has worked with meta-build systems like NAnt and SCons on major game projects, yet can't understand the most basic things about how CMake works or find a tutorial answering these questions.
In the past, I have essentially hacked around not understaning find_package by setting all the foo_DIR values by hand as CMake complains until I get a working folder.
I would like to run through a simple example which I'm working on right now, and dearly hope someone can explain what I'm doing so wrong.
Firstly, some assumptions:
I want to build everything for both MacOS and Windows, ideally via CMakeGUI. MacOS should build XCodeProjects and Windows should build Visual Studio Solutions.
Where there are dependencies, I want to compile them myself, so I have debug symbols and can modify the dependency source (or at least debug into it.)
No installation of pre-built binaries into system folders, i.e. no use of sudo port install opencv/pcl, etc on mac.
I have multiple projects, and prefer to keep a project and its dependencies in a single folder.
For the purposes of a concrete example, suppose I am building this project, although it's an arbitrary choice to illustrate the process and confusion I suffer:
https://github.com/krips89/opendetection
This lists dependencies, which I have intentionally reordered here so that I can take them in order, as follows:
find_package(OpenCV REQUIRED)
find_package(Eigen REQUIRED)
find_package(Boost 1.40 COMPONENTS program_options REQUIRED )
find_package(PCL REQUIRED)
find_package(VTK REQUIRED)
I would like to have all of these dependencies downloaded and configured in a single path (let's say c:\src on Windows, and ~\src on Mac for simplicity), NOT in a system path. Assume that the actual folder is a sub-folder for this project, and no a sub-folder for all projects. This should also allow for side-by-side installation of multiple projects on the same computer.
Taking this one step at a time:
(1) I clone openCV from https://github.com/opencv/opencv, sync to tag 3.1, configure into the folder opencv_build folder, build and install into opencv_install. I've done this so many times it's pretty straightforward.
(2) As above, but for eigen (although building for eigen doesn't actually do anything s it's a template library. I install to a folder eigen_install
Taking directory shows a series of folders for downloaded dependencies. I have assumed a convention where , and are source repos, and their following _build folders are the "WHere to build the binaries" folders in CMakeGui.
$ ls
boost_1_40_0 opencv opendetection_build
eigen opencv-build opendetection_data
eigen_build opencv_contrib pcl
eigen_install opendetection
All good so far, now let's try to configure opendetection and generate a solution into opendetection_build, and find pendetection's dependencies from within the ~/src folder, that is for the first two dependencies, I hope to find opencv and eigen in the opencv-build and eigen-build folders.
OpenCV immediately fails, as expected, saying:
Could not find a package configuration file provided by "OpenCV" with any of the following names:
OpenCVConfig.cmake
opencv-config.cmake
Add the installation prefix of "OpenCV" to CMAKE_PREFIX_PATH or set "OpenCV_DIR" to a directory containing one of the above files. If "OpenCV" provides a separate development package or SDK, be sure it has been installed.
That's good, because I want to explicitly tell CMake to look for dependent packages under my ~/src folder. Question: Is the use of CMAKE_PREFIX_PATH=/users/foo/src the recommended way to accomplish what I want - looking for all sub-packages under a specific path?
Following this, CMake finds OpenCV (good), and sets OpenCV_DIR = /Users/foo/src/opencv-build.
Question: Given that I have made an "install" to opencv-install (using CMAKE_INSTALL_PREFIX and building the Install Target Of OpenCV, shouldn't it find OpenCV in the opencv-install folder not opencv-build?
Moving on to eigen, I have configured and built eigen, and installed it to ~/src/eigen-install, which since it is a subfolder of CMAKE_PREFIX_PATH (~/src) I might expect to be found. But it doesn't seem to be. Can somebody explain to me what I'm not understanding? Particularly given that Eigen in a template library, and that there are at least three folders (eigen, eigen_build and eigen_install) under CMAKE_PREFIX_PATH which I would have thought CMake would find something in, I assume I must be doing something wrong here. I KNOW from past experience, I can set EIGEN_INCLUDE_DIR by hand in CMakeGUI by hand, and continue hacking forth, but that just seems wrong.
I'm more than willing to write up a web page explaining this for future people as dumb as me if one does not already exist, although I can't understand how use of CMake for basic project configuration and generation is apparently so obvious to everyone but so opaque for me. I have actually been using CMake for some years, usually by just manually setting Boost_INCLUDE_Dir, Foo_INCLUDE_PATH etc manually, but clearly this is not the right solution. Generally, after spending a couple of days fighting through the various packages to generate a solution by manually setting INCLUDE PATHS, LIBRARY PATHS and other options, I just deal with the solution and don't touch CMake again. But I would love to understand what I'm missing about find_package for my (surely not uncommon) use case of wanting to control my project dependencies rather than just using sudo port install * and installing random versions of projects to my global system folders.
As error message says, CMAKE_PREFIX_PATH should be set to installation prefix of the package. E.g., if the package has been built using CMake, this is CMAKE_INSTALL_PREFIX variable's value, if the package has been build using Autotools, this is value of --prefix option used for configure it, and so on.
CMake doesn't search every directory under CMAKE_PREFIX_PATH. That is why specifying it as /users/foo/src is useless if you have the package installed at /users/foo/src/eigen-install.
Instead, you may install all 3d-party packages into /users/foo/src/install, and use that path as CMAKE_PREFIX_PATH in your main project.