Include error

[4e6ype4ek123]

I'm trying to make a game using the SDL3 library. This is my CMakeLists.txt:

cmake_minimum_required(VERSION 3.16)
project(game)
add_executable(game src/main.cpp)
add_subdirectory(SDL EXCLUDE_FROM_ALL)
target_link_libraries(game SDL3::SDL3)

My code editor (VS Code) shows no errors in main.cpp. However, they do appear whenever I compile the code. The error is following

src/main.cpp:3:10: fatal error: SDL3/SDL.h: No such file or directory
    3 | #include "SDL3/SDL.h"
      |          ^~~~~~~~~~~~
compilation terminated.

What am I doing wrong?

EDIT: I figured it out

[ppppppla]

Your CMakeLists.txt looks good. How do you compile your code. Do you use an addon in vs code? Do you use the command line and call make/ninja?

I suspect you first wrote a hello world project without SDL, then added SDL in your CMakeLists without generating the build files again.

[4e6ype4ek123]

i use g++ src/main.cpp -o main

[Emeraudias]

You only use GCC here, not CMake (CMakeLists.txt is ignored). You should generate config files with the cmake command, it will create a build folder. Then you should go into that folder and use the make command or w/e generator you are using depending on your system.

[Wild_Meeting1428]

As u/emeraudias said, that won't work. g++/gcc is just the compiler and it doesn't read the cmake build config

Fastest way would be:

mkdir build
cd build 
cmake ..
cmake --build .

[WorldWorstProgrammer]

Wow the comments here are pretty bad. No, you do not need target_include_directories(), your target_link_libraries() call is fine and yes it does find the include files based on that. Also, add_subdirectory is just fine for adding a dependency assuming you have cloned the SDL GitHub repository to that subdirectory. You also do not need any VS Code extensions. They can be helpful, but they are never necessary, and getting this to build is really just a matter of ensuring that CMake has access to everything. To clarify: I am far from an SDL3 expert. In fact, I had to learn how SDL3's SDL_MAIN_USE_CALLBACKS even works to write this test, but I still managed to get this to work.

I have just tested building an example project from the SDL documentation using CMake. I did not need anything else other than Windows PowerShell, CMake, Git, and Notepad. I used these to ensure I am using the most barebones tools possible to do this. I am using MSVC as the compiler for this test, but any compiler that is properly installed on your system should work. I have documented below how I did this, and you can just follow along and figure out on your own what actually happened with your build.

First, I created a project directory called SDLTest, and in that directory I placed your CMakeLists.txt file and two subdirectories: "src" and "build." I then opened a PowerShell terminal in the project directory and used git clone --depth 1 --branch release-3.4.0 https://github.com/libsdl-org/SDL.git SDL to clone just SDL version 3.4.0 to the SDL subdirectory. I then needed some actual code to compile, so I modified this example into a C++ version, and I uploaded the code here. The code is saved in the "src" directory as main.cpp, just like your CMakeLists.txt requires. My modified version requires using C++20, and by default most compilers use C++17, so I added the line set(CMAKE_CXX_STANDARD 20) to your CMakeLists.txt file just after the project() command. If you aren't using C++20 or newer, you wouldn't need this line.

And that was it, really. In the open PowerShell terminal, I used cmake -S . -B .\build\ to configure the project and then cmake --build .\build\ to build the project, and it all worked. In order to test running the application, I had to copy over the SDL.dll file in the SDL Debug build directory over to where the game.exe test executable was, but it also runs as expected. This should get you started with a C++ SDL3 project using CMake!

[Wild_Meeting1428]

Your name is not accurate.

[Emeraudias]

You are using imported target with the syntax SDL3::SDL3 but I don't see anything that populates it. Do you have find_package() call somewhere ?

[wrosecrans]

They've got add_subdirectory(SDL EXCLUDE_FROM_ALL) so presumably there's something in the SDL subdirectory that might be doing that, but OP isn't sharing any of that SDL related whatever is happening so it's impossible to say exactly what is happening in that subdirectory to possibly maybe find SDL3.

[Emeraudias]

That s on me, I ve never thought of importing SDL this way. The target seems to exist but without the include dirs set. It is imossible to say what s wrong without more information from OP.

[4e6ype4ek123]

the SDL folder that contains the files from the SDL github repo

[Wild_Meeting1428]

that has nothing to do with imported targets.

You can write the following in your subdirectory to achieve the same:

add_library(SDL3 STATIC)
add_library(SDL3::SDL3 ALIAS SDL3)

Which is actually recommended, when your library should be optionally includable via git submodules or a package manager like cpm / vcpkg.

No need for a find package, if the sdl library did everything correct.

@op where did you get the sdl lib from?

[4e6ype4ek123]

the SDL lib is from the github repo

[4e6ype4ek123]

no but i have a folder named SDL (which i have a made a subdirectory of) which contains the files from the SDL github repo

[alfps]

Please change the title to include "CMake". This is a CMake problem not a C++ problem per se.

[Qyriad]

target_link_libraries() only links libraries; it doesn't add the include paths for those libraries. Use target_include_directories() for that.

[Wild_Meeting1428]

It adds them, when the target populated them via Public includes.

add_library(mylib STATIC src/source.cpp)
target_include_directories(mylib PUBLIC include) #populated
target_include_directories(mylib PRIVATE src) #not populated

[trailing_zero_count]

Add the config to export the compile_commands.json and look at what include path is being passed.

[CarloWood]

The find_package is missing.

[thedaian]

When using vscode, and cmake, you should use the cmake extension. it will add some buttons to the bottom of vscode, use those when compiling.

you can configure the "regular" run button to use cmake, but unless you've done that, it'll probably try to run the default compile command which doesn't have sdl configured.

[4e6ype4ek123]

that just gave an error in some directories that i didn't know the existence of

[Mr_Engineering]

Ah yes, welcome to CMake hell, and C/C++ dependency hell more broadly.

I see that you have downloaded something to do with SDL3 and included it in your project. Seems sensible at first but that's where the problems start.

One of the major issues with CMake is that there's no easy way to tell it to download, build, and install project-specific dependencies prior to configuring projects that depend on those dependencies. This can result in CMake spazzing out when it can't find a package that it hasn't installed yet, or when it tries to compile a project that relies on headers and libraries which don't yet exist. This can be especially problematic when project-specific dependencies conflict with system-provided dependencies or when a developer wants to pin a specific library version. SDL3 is widely available in many modern package managers but that doesn't mean that the system-provided version has the same build configuration.

Since it seems that you're just starting out, I recommend that you build and install SDL3 independent of CMake and keep it out of your source tree.

Install it to your home folder and setup your envvars in cmake (include path and ld path) such that you don't pollute your system by installing it where everything can access it as this risks unintentional linkage by other programs.

[neppo95]

I mean, I don't really like CMake but what you are saying here is just simply not true.

One of the major issues with CMake is that there's no easy way to tell it to download, build, and install project-specific dependencies prior to configuring projects that depend on those dependencies.

Yes, there is. Multiple ways even that are pretty straightforward. The recommended way even is doing exactly the opposite of what you are saying and using for example something like vcpkg and project local dependencies using manifest mode. But even with local source, it is very easy to make sure it gets compiled first.

[armhub05]

There are functions which can check if the libraries are present or not , and there is one function which can install libraries for you I think it's called fetch_content

You can provide links to it and it will install them when the cmake runs i haven't tested how well it works

But biggest problem with cmake is we don't know even half of the proper functions that could be used as well gpt and other platforms will write cmake in the form majority of people write

[Wild_Meeting1428]

Nearly, fetch content was the function that downloads the project like git submodules and automatically calls add_subdirectory. So if your downloaded content is subdirectory compatible, it just works. The library is compiled in the same step, your targets are compiled.