CPack can be used to generate many different types of packages for distribution. When generating the build system, the CPack instructions we listed in CMakeCPack.cmake are used to generate a CPackConfig.cmake file in the build directory. When running the CMake command for the package or package_source targets, CPack is automatically invoked with the autogenerated configuration file as argument. Indeed, these two new targets are simple rules that wrap calls to CPack. Much as CMake, CPack also has a concept of generators. Whereas generators in the context of CMake are the tools that will be used to generate the native build scripts, for example, Unix Makefiles or Visual Studio project files, in the context of CPack these are the tools to be used for packaging. We listed these, exercising particular care for the different platforms, using the CPACK_SOURCE_GENERATOR and the CPACK_GENERATOR variables for the source and binary packages, respectively. Thus the Debian packaging utilities will be invoked for the DEB package generator, whereas the appropriate archiving tool on the given platform will be invoked for the TGZ generator. We can invoke CPack directly from the build directory and select which generator to use with the -G command-line option. The RPM package can be generated with the following:

$ cd build
$ cpack -G RPM

CPack: Create package using RPM
CPack: Install projects
CPack: - Run preinstall target for: recipe-01
CPack: - Install project: recipe-01
CPack: Create package
CPackRPM: Will use GENERATED spec file: /home/user/cmake-cookbook/chapter-11/recipe-01/cxx-example/build/_CPack_Packages/Linux/RPM/SPECS/recipe-01.spec
CPack: - package: /home/user/cmake-cookbook/chapter-11/recipe-01/cxx-example/build/recipe-01-1.0.0-Linux.rpm generated.

For any distribution, be it source or binary, we need to package only those contents that will be strictly necessary for the end user, hence the entire build directory and any other file related to version control will have to be excluded from the list of files to be packaged. In our example, the exclusion list was declared with the following command:

set(CPACK_SOURCE_IGNORE_FILES "${PROJECT_BINARY_DIR};/.git/;.gitignore")

We also need to specify basic information about our package, such as the name, a short description, and the version. This information is set by means of CMake variables, which are then passed on to CPack when including the corresponding module.

Let us look in detail at the instructions for the different kinds of packages we can generate for our example project.