For a brief user-level introduction to CMake, watch C++ Weekly, Episode 78, Intro to CMake by Jason Turner. LLVM’s CMake Primer provides a good high-level introduction to the CMake syntax. Go read it now.

After that, watch Mathieu Ropert’s CppCon 2017 talk Using Modern CMake Patterns to Enforce a Good Modular Design (slides). It provides a thorough explanation of what modern CMake is and why it is so much better than “old school” CMake. The modular design ideas in this talk are based on the book Large-Scale C++ Software Design by John Lakos. The next video that goes more into the details of modern CMake is Daniel Pfeifer’s C++Now 2017 talk Effective CMake (slides).

This text is heavily influenced by Mathieu Ropert’s and Daniel Pfeifer’s talks.

If you are interested in the history and internal architecture of CMake, have a look at the article CMake in the book The Architecture of Open Source Applications.

Modern CMake is only available starting with version 3.0.0.

CMake is code. Therefore, it should be clean. Use the same principles for CMakeLists.txt and modules as for the rest of the codebase.

For example, a project might use a common set of compiler warnings. Defining such properties globally in the top-level CMakeLists.txt file prevents scenarios where public headers of a dependent target causing a depending target not to compile because the depending target uses stricter compiler options. Defining such project properties globally makes it easier to manage the project with all its targets.

Those commands operate on the directory level. All targets defined on that level inherit those properties. This increases the chance of hidden dependencies. Better operate on the targets directly.

Different compilers use different command-line parameter formats. Setting the C++ standard via -std=c++14 in CMAKE_CXX_FLAGS will brake in the future, because those requirements are also fulfilled in other standards like C++17 and the compiler option is not the same on old compilers. So it’s much better to tell CMake the compile features so that it can figure out the appropriate compiler option to use.

As an example, don’t add -Wall to the PUBLIC or INTERFACE section of target_compile_options, since it is not required to build depending targets.

Starting with CMake 3.4, more and more find modules export targets that can be used via target_link_libraries.

Don’t fall back to the old CMake style of using variables defined by external packages. Use the exported targets via target_link_libraries instead.

CMake provides a collection of find modules for third-party libraries. For example, Boost doesn't support CMake. Instead, CMake provides a find module to use Boost in CMake.

CMake dominates the industry. It’s a problem if a library author does not support CMake.

It’s possible to retrofit a find module that properly exports targets to an external package that does not support CMake.

See Daniel Pfeifer’s C++Now 2017 talk Effective CMake (slide 24ff.) on how to do this. Keep in mind to export the right information. Use BUILD_INTERFACE and INSTALL_INTERFACE generator expressions as filters.

t.b.d. (see beginning of Daniel Pfeifer’s talk)

CMake is a build system generator, not a build system. It evaluates the GLOB expression to a list of files when generating the build system. The build system then operates on this list of files. Therefore, the build system cannot detect that something changed in the file system.

CMake cannot just forward the GLOB expression to the build system, so that the expression is evaluated when building. CMake wants to be the common denominator of the supported build systems. Not all build systems support this, so CMake cannot support it neither.

It just makes things simpler. See Dashboard Client via CTest Script for more information.

This simplifies filtering by regex when running tests via CTest.