What exacly is "buidling" from source and how does it work

Question

So I really cant understand how this work but late me explain. First, just in case you need it, I am running Ubuntu 12.04 64-bit on a laptop.

As a building tool am using CMake. I want to load in to my project OpenCV, MRPT (http://www.mrpt.org/) and libfreenect. All of them have a "source code". What I don't understand is when they say "build from source". How to I make a project with all of them? Do I need to build each one individually and with some way but then in my project OR do I down load the source code and build them all together at ones? As you can see I'm really confused what I have to do... do I run the CMakeList.txt from each source code and the run one CMakeList.txt that has all the other CMakeList.txt?

In fewer world, if I want to build from source, two or more libraries, how do I do that?

I would like a general answer (how this "build from source" works) and an answer specifically on the the ones I mentioned (CMake, OpenCV, MRPT, libfreenect). I hope I made clear what I don't really understand.

Answer 1

It depends of the 'master' project. In general in the c/c++ universe your project must know how to invoke the build process of each subproject/library OR your project needs to know how to include&link the results after building each external project yourself.

You can also mix the two approaches if needed but I think it cleaner to try to use one if possible.

In the first case if all the subprojects offer cmake building files (CMakeLists.txt) you may try to add_subdirectory() each and see if there are any conflicts. For example google test can be easily included this way and it gives your project some global variables that easy linking later.

Alternatively or if the above approach gives problems or the sub project doesn't provide CMakeLists.txt you can use ExternalProject_add(). It takes more work and you have to handle includes/linking configurations with your project manually but it makes the subproject more independent. For example if there are conflicting targets with your project or the subproject doesn't provide CMakeLists.txt.

The last approach involves building and installing the sub projects separately, using configuration variables in your project to point the includes/libraries paths of the sub project. Check CMake:How To Find Libraries for details.