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