Edgar Luque - cmake

Creating precompiled headers with cmake

2020-11-12T00:00:00+00:00

What are precompiled headers?</h2>
They are a partially processed version of header files, this speeds up compilation because it doesn't have to repeatedly parse the original header.</p>

How to use it</h2>

The way to do it is to pass the header files you want precompiled to the target_precompile_headers</code> command.</p>

Imagine this folder structure:</p>

.</span></span>
├── CMakeLists.txt</span></span>
└── src</span></span>
    ├── header.h</span></span>
    └── main.cpp</span></span>
</span>
1 directory, 3 files</span></span></code></pre>
Now we create a very basic CMakeLists.txt:</p>
cmake_minimum_required</span>(VERSION 3.16)</span></span>
</span>
project</span>(MyProject)</span></span>
</span>
set</span>(HEADER_FILES</span></span>
	src/header.h)</span></span>
</span>
set</span>(SOURCE_FILES</span></span>
	src/main.cpp</span></span>
	${HEADER_FILES}</span></span>
	)</span></span>
</span>
include_directories</span>(src)</span></span>
</span>
add_executable</span>(MyProject </span>${SOURCE_FILES}</span>)</span></span></code></pre>
Notice we require a minimum cmake version of 3.16, this is due to target_precompile_headers</code> being added in that version.</p>
We add the command after the add_executable</code> instruction to the private scope.</p>
It's recommended to use the private scope to prevent precompiled headers appearing in an installed target, consumers should decide whether they want to use precompiled headers or not.</p>
target_precompile_headers(MyProject PRIVATE</span> ${HEADER_FILES}</span>)</span></span></code></pre>
When compiling you can see now that it indeed compiles the headers:</p>
Scanning dependencies of target MyProject</span></span>
[ 33%] Building CXX object CMakeFiles/MyProject.dir/cmake_pch.hxx.gch</span></span>
[ 66%] Building CXX object CMakeFiles/MyProject.dir/src/main.cpp.o</span></span>
[100%] Linking CXX executable MyProject</span></span>
[100%] Built target MyProject</span></span></code></pre>



Setting Up SDL2 with CMake
2019-04-27T00:00:00+00:00
Installing CMake</h2>
Most common distributions have cmake available on their package manager repostories:</p>
# Debian based</span></span>
sudo</span> apt install cmake</span></span>
</span>
# Arch</span></span>
pacman</span> -S</span> cmake</span></span></code></pre>Install SDL2 libraries</h2>
I only know about the debian based ones, if you are on another distro you should look them up.</p>
sudo</span> apt install libsdl2-dev libsdl2-image-dev libsdl2-mixer-dev libsdl2-net-dev libsdl2-ttf-dev libsdl2-gfx-dev</span></span></code></pre>Directory Structure</h2>
Here is a common directory structure when using cmake to find packages:</p>
├── cmake</span></span>
│   ├── FindSDL2.cmake</span></span>
│   ├── FindSDL2_mixer.cmake</span></span>
│   └── FindSDL2_net.cmake</span></span>
├── CMakeLists.txt</span></span>
└── src</span></span>
    └── main.cpp</span></span></code></pre>
You can find the cmake files to find SDL2 and it's components
here</a></p>
Or you can use this simple command:</p>
cd</span> cmake</span></span>
wget</span> https://raw.githubusercontent.com/aminosbh/sdl2-cmake-modules/master/FindSDL2{,_gfx,_image,_mixer,_net,_ttf}.cmake</span></span></code></pre>Creating the CMakeLists.txt file</h2>
cmake_minimum_required</span>(VERSION 3.13)</span></span>
project</span>(MyProject)</span></span>
</span>
# Needed so that cmake uses our find modules.</span></span>
list</span>(APPEND CMAKE_MODULE_PATH</span> ${CMAKE_CURRENT_SOURCE_DIR}</span>/cmake)</span></span>
</span>
find_package</span>(SDL2 REQUIRED)</span></span>
find_package</span>(SDL2_net REQUIRED)</span></span>
find_package</span>(SDL2_mixer REQUIRED)</span></span>
find_package</span>(SDL2_image REQUIRED)</span></span>
find_package</span>(SDL2_gfx REQUIRED)</span></span>
find_package</span>(SDL2_ttf REQUIRED)</span></span>
</span>
</span>
set</span>(SOURCE_FILES</span></span>
    src/main.cpp</span></span>
    )</span></span>
</span>
include_directories</span>(src)</span></span>
</span>
add_executable</span>(MyProject </span>${SOURCE_FILES}</span>)</span></span>
target_link_libraries</span>(MyProject SDL2::Main SDL2::Net SDL2::Mixer SDL2::Image SDL2::TTF SDL2::GFX)</span></span>
</span></code></pre>
And thats it! Now you can remove the SDL2 components you don't want to use.</p>
Building</h2>
Following the standard cmake procedure:</p>
mkdir</span> build</span></span>
cd</span> build</span></span>
cmake</span> ..</span></span>
make</span> -j$</span>{nproc}</span></span></code></pre>

Edgar Luque - cmake

Creating precompiled headers with cmake

What are precompiled headers?</h2> They are a partially processed version of header files, this speeds up compilation because it doesn't have to repeatedly parse the original header.</p>

Setting Up SDL2 with CMake

Building</h2> Following the standard cmake procedure:</p> mkdir</span> build</span></span> cd</span> build</span></span> cmake</span> ..</span></span> make</span> -j$</span>{nproc}</span></span></code></pre>

What are precompiled headers?</h2>
They are a partially processed version of header files, this speeds up compilation because it doesn't have to repeatedly parse the original header.</p>

Building</h2>
Following the standard cmake procedure:</p>
`mkdir</span> build</span></span> cd</span> build</span></span> cmake</span> ..</span></span> make</span> -j$</span>{nproc}</span></span></code></pre>`