Tuesday Coding Tip 23 — CMake configure_file

Tue, 22 Sep 2026 09:59:00 +0000

Tuesday coding tips are super short posts about various tidbits mainly from C++, but also from other programming languages I use. You can also follow the #TuesdayCodingTips hashtag on Mastodon and Linkedin.

In unit tests, I often don’t want to bother with the working folder of the test binary. But if those tests need physical files from the disc, I need to know their absolute paths (which are different on each machine). Luckily, CMake has a function configure_file that can write CMake variables to a file template.

cmake_minimum_required ( VERSION 3.10 )

set ( USE_MSVC_FEATURES ("${CMAKE_GENERATOR}" MATCHES "Visual Studio 17 2022") )

project ( DEMO CXX )

# CMakeLists.txt
configure_file(
    "${CMAKE_SOURCE_DIR}/TemplateHeader.hpp.in" # input
    "${CMAKE_SOURCE_DIR}/FinalHeader.hpp" # output
)

For example, I can prepare a template for a header that will hold an absolute path to a folder with helper files, and during configuration, I can produce a valid C++ header with the path filled out. CMake will replace variables escaped as @VAR@, ${VAR}, $CACHE{VAR} or $ENV{VAR} and furthermore it can do things like generating #define directives.

// TemplateHeader.hpp.in
#pragma once

#include <filesystem>

#cmakedefine01 USE_MSVC_FEATURES

const std::filesystem::path TESTDATA_FOLDER = "@CMAKE_CURRENT_SOURCE_DIR@/TestFiles";

// Generated FinalHeader.hpp
#pragma once

#include <filesystem>

#define USE_MSVC_FEATURES 1

const std::filesystem::path TESTDATA_FOLDER = "C:/Work/Project/TestFiles";

Full documentation: https://cmake.org/cmake/help/latest/command/configure_file.html

Tuesday Coding Tip 10— CTest

Tue, 05 May 2026 09:59:00 +0000

CMake can do many things and instrumenting your test suite is one of them. Use add_test to tell cmake it should run a particular command with given parameters. If it returns zero, it succeeded. You can use it to simply run a testrunner binary or to make a matrix of input parameters that are expected to not crash the program.

cmake_minimum_required ( VERSION 3.26 )

project ( testrunner )
add_executable ( ${PROJECT_NAME} Main.cpp )

enable_testing()
add_test(
   NAME "Example with no params"
   COMMAND ${PROJECT_NAME}
)

add_test(
   NAME "Example with help param"
   COMMAND ${PROJECT_NAME} -h
)

In order to add_test do anything, one has to also call enable_testing(). Running the tests is just a matter of running ctest from command line. Just note that ctest requires you to specify a build configuration if you have more than one.

Coder Legion - Recent posts tagged cmake

Tuesday Coding Tip 23 — CMake configure_file

Tuesday Coding Tip 10— CTest