Using Third Party Libraries¶
Felix is specifically designed to be able to use third party C and C++ libraries, and to be able to do so without any makefiles, linkage commands, or other scripts.
To make this happen, there is a configuration database which tells Felix where the relevant header files and libraries actually reside in your file system.
In fact, Felix itself uses the very same machinery to use its own native libraries.
Felix can build for any targets you can configure. The default, required, target is called host, and it is your normal programming environment.
Felix splits its data into two parts, shared and the target, usually host. The data in shared is common to all targets; it consists of all platform independent data, including Felix source libraries, and platform independent C++ header files.
In the target host you will find object files and executables compiled for your specific operating system by the C++ compiler toolchain selected as the default.
Inside every platform dependent target, there is a directory called config, you can examine it here from the Felix install directory:
You will see a bunch of files ending in extension .fpc. Each of these files specifies how to use a package with the basename of the file. Lets look at one:
~/felix>cat build/release/host/config/sdl2.fpc Generated_from: 3674 "/Users/skaller/felix/src/packages/sdl.fdoc" Name: SDL2 Description: Simple Direct Media Layer 2.0 cflags: -I/usr/local/include/SDL2 includes: '"SDL.h"' provides_dlib: -L/usr/local/lib -lSDL2 provides_slib: -L/usr/local/lib -lSDL2 requires_dlibs: ---framework=OpenGL requires_slibs: ---framework=OpenGL
This is the one on my Mac, which runs OSX. The first line tells how the file got produced, the second is a common name for the library which is just documentation too, as is the third line, which gives more information.
But now come the important lines.
- cflags tells the C++ compiler how to find the SDL header file
- includes tells Felix what the header file name is
- provides_dlib tells C++ how to link the dynamic version of the SDL2 library
- provides_slib tells C++ how to link the static version of the SDL2 library
- requires_dlibs tells C++ about dependencies of SDL2 dynamic library
- requires_slibs tells C++ about dependencies of SDL2 dynamic library
Note that values of these attributes are specific to your computer, and also sometimes to the C++ compiler selected.
When you install a third party library, you have to create an entry similar to that seen above for the library in the configuration database for each target where you want to use that library.
On Ubuntu, you will normally only need three lines
includes: '"mylib"' provides_dlib: -lmylib provides_slib: -lmylib
because C++ will automatically look in /usr/lib for libraries, and in /usr/include for header files. Do not include the leading lib of library file names, nor the trailing .so!
Felix Source Code¶
Now you have installed your library, and added entries in the configuration database, you can use the library like this:
type mytype = "mylib::mytype" requires package "mylib" ;
This Felix code lifts the C++ type mylib::mytype into Felix, naming it mytype in Felix, and it tells Felix that the library providing that C++ types is in package mylib .. which of course is just the name of the file mylib.fpc in the configuration database.
This is how Felix maps abstract component name used in source code into the compilation and linker switches needed to use the C++ and binary library components.
The source code is therefore platform independent, and you can run programs which uses third party libraries without specifying any linker switches or other platform specific nonsense every again. You have to specify it once, in the configuration database.
Felix is smart, it will only link the library if it is actually required. If you do not use values of the type mytype then the library will not be linked, if you do, it will be.