[CMake] Explanation of the CMake INSTALL and EXPORT Commands

Thu Apr 4 15:32:00 EDT 2013

Thanks for the very valuable info Matthew.

If Project A is installed (to a standard location), then it is available
> system wide, yes. However you should still use find_package(A) rather
> than relying on e.g. target_link_libraries(B A)

I tried to use find_package(A) but CMake would display a warning:

"By not providing "FindA.cmake" in CMAKE_MODULE_PATH this project has asked
CMake to find a package configuration file provided by "A", but CMake did
not find one"

Obviously I am not installing it correctly. When do I know my
libraries/package is installed correctly (apart from the fact that
find_package will be able to find it)? Is there a specific folder that I
can check to make sure the installation took place properly and that CMake
will be able to find the libraries/packages? Am I correct in assuming that
if I do the install correctly, I do not have to write a package
configuration file and that it will be provided by CMake automatically?

Any tips that first time users like me should watch out for when installing
their libraries would be great.

Generally speaking, you should either have two separate builds of A in
> 32- and 64-bit mode that can be installed in parallel

I will follow your advice here and split up the configurations.

Thank you,
Saad

Message: 2
> Date: Wed, 03 Apr 2013 17:12:43 -0400
> From: Matthew Woehlke <matthew.woehlke at kitware.com>
> Subject: Re: [CMake] Explanation of the CMake INSTALL and EXPORT
>         Commands
> To: cmake at cmake.org
> Message-ID: <kji607$pe$1 at ger.gmane.org>
> Content-Type: text/plain; charset=UTF-8; format=flowed
> On 2013-04-03 16:16, Saad Khattak wrote:
> > I am having a hard time understanding some commands in CMake which by the
> > looks of it are vital for proper project deployment. One of the commands
> is
> > INSTALL and the other is EXPORT.
> There are two forms of EXPORT, and I am not certain which one you are
> referring to. There is the command EXPORT, and there is the EXPORT named
> argument to the INSTALL command. They are similar in that they both deal
> with generating target export files, but the command version is used to
> generate such for build trees, while the named argument version applies
> to install trees.
> If you never use your software downstream from a build directory, you
> can safely ignore the command version.
> > 1) Why do I need to install my library/executable? When I build my
> > libraries and they are put in their library output paths, what is the
> point
> > of INSTALL?
> INSTALL is used to implement 'make install' (or equivalent), and also
> packaging. If you are only ever using your software from a source build,
> you can probably ignore it. If you ever want to deploy your software,
> however, I would strongly encourage having an install process.
> Installing makes a software package generally available to users of the
> system, by installing its components into a well-known prefix (e.g.
> /usr, /usr/local, /opt/MySoft). It is often much more convenient to use
> an installed software package rather than stuff in a build directory, as
> installed binaries tend to be in e.g. PATH, whereas build directories
> may not be readable by all users.
> Please don't teach your build to write its build objects directly into
> e.g. /usr/local/bin :-).
> > 2) Once I do install targets and/or programs, are they available to other
> > projects that are not in the same CMakeLists build?
> Yes. They are available just from build directories also, but you will
> need to manually tell CMake where to find build directories. (Per above,
> installed packages can be found automatically if they are installed to
> standard (well known) locations... keeping in mind that you can choose
> to install to any location you like, e.g. in your home directory.)
> (If you are using exported targets - and you should - then you will need
> to use the EXPORT command to create a build-directory exported targets
> file. Getting this right is a little more complicated than install
> exports, but saves needing to install the package every time your
> downstream needs an updated version.)
> > 3) Suppose I have 2 completely separate projects (i.e. they have
> completely
> > separate CMakeLists that are not 'talking' to each other) - Project A
> > builds some libraries which Project B now needs to use. Does Project A
> > 'install' the libraries and are now those libraries are available system
> > wide?
> If Project A is installed (to a standard location), then it is available
> system wide, yes. However you should still use find_package(A) rather
> than relying on e.g. target_link_libraries(B A) so that your build will
> work for users that do not have A in a standard location.
> If A is built by CMake, your install should generate exports so that
> users of A do not need a find module. (Also, then you *can* - and should
> - do target_link_libraries(B A), because 'A' will be an imported target,
> i.e. will 'look like' it was build as part of B.)
> > 4) Project A can build 32 bit and 64 bit libraries. How does INSTALL (or
> > EXPORT? Like I said earlier, I am very confused here...) know which
> library
> > it is 'installing'? And then how does Project B 32 bit know to link with
> > Project A 32 bit libraries and same with 64-bit?
> Hmm... I'm not all that familiar with multi-arch bits, but I *think* how
> this is supposed to work is that when B does find_package(A), it will
> look in either lib or lib64 depending on whether or not it is being
> built in 64-bit mode. So as long as your find_package picks the right
> AConfig.cmake, all will be well (it should by default if A is installed
> to a standard location, and/or if necessary you can force where to find
> its config).
> Generally speaking, you should either have two separate builds of A in
> 32- and 64-bit mode that can be installed in parallel, or else A should
> produce 32- and 64-bit libraries with different names. (I would
> recommend the former, since that is how most software works and is less
> likely to give you headaches getting it to work. Also because getting
> CMake to build both 32- and 64-bit binaries in the same build is going
> to be harder than just having separate 32- and 64-bit builds.)
> Hope that helps.
> --
> Matthew
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