Linking SDL2 with CMake

Question

I'm having problems linking SDL2 to my project, which probably are because I'm new to CMake, and I don't fully know how to create new projects with it. Every time and method I've tried to fix this problem has resulted in one of the following problems:

1. "Cannot locate WinMain@16"
2. Multiple undefined reference errors
3. undefined reference to `SDL_main`

I have attempted to use find_package, linking directly to files, linking to library files, following tutorials (for example https://trenki2.github.io/blog/2017/06/02/using-sdl2-with-cmake/), searching for answers (most of them talk about using find_package which I can't get to work) (for example Using SDL2 with CMake).

Project dependencies

SDL 2.0.12, CMake 3.17.0, 7-Zip, mingw32-make, wget

The project is supposed to be cross-platform, but the main devenv is Windows 10. All scripts are run from the root folder "vivaria".

Project structure

vivaria/
├── build/
│   └── [cmake build files]
├── buildtools/
│   └── SDL2/SDL2-2.0.12/lib/x86 (and x64)
│                            ├── SDL2.lib
│                            └── SDL2main.libs
├── deploy/
├── resources/
├── scripts/
│   ├── build_windows_debug_x86.bat
│   └── install_buildtools_windows.bat
└── src/
    ├── CMakeLists.txt
    └── vivaria.cpp

build_windows_debug_x86.bat

cmake -G "MinGW Makefiles" -S .\src\ -B .\build\ -DCMAKE_BUILD_TYPE=Debug
cd .\build\
mingw32-make

vivaria.cpp

#include <iostream>
#include "SDL.h"

int main() {
    if (SDL_Init(SDL_INIT_VIDEO) != 0){
        std::cout << "Hello world" << std::endl;
        return 1;
    }
    
    SDL_Quit();
    return 0;
}

CMakeLists.txt: undefined reference to SDL_main

cmake_minimum_required(VERSION 3.17)
project(Vivaria VERSION 1.0.0)

set(CMAKE_CXX_GLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -lmingw32")
# set(CMAKE_EXE_LINKER_FLAGS "-static-libgcc -static-libstdc++")

set(INCLUDE_DIR "${CMAKE_SOURCE_DIR}/../buildtools")
set(SDL2_DIR "${INCLUDE_DIR}/SDL2/SDL2-2.0.12")

set(SDL2_INCLUDE_DIRS "${SDL2_DIR}/include")
set(CMAKE_BINARY_DIR "${CMAKE_SOURCE_DIR}/../deploy")

# Support both 32 and 64 bit builds
if (${CMAKE_SIZEOF_VOID_P} MATCHES 8)
    set(SDL2_LIBRARIES "${SDL2_DIR}/lib/x64/SDL2main.lib;${SDL2_DIR}/lib/x64/SDL2.lib")
else ()
    set(SDL2_LIBRARIES "${SDL2_DIR}/lib/x86/SDL2main.lib;${SDL2_DIR}/lib/x86/SDL2.lib")
endif ()

# link dependencies
include_directories(${SDL2_INCLUDE_DIRS})
link_directories(${SDL2_LIBRARIES})

# Project files and linking
set(SOURCES vivaria.cpp)
add_executable(${PROJECT_NAME} vivaria.cpp)
target_link_libraries(${PROJECT_NAME} ${SDL2_LIBRARIES})

Console output

F:\Koodit\Vivaria\build>mingw32-make
[ 50%] Linking CXX executable Vivaria.exe
c:/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../../mingw32/bin/ld.exe: F:/Koodit/Vivaria/src/../buildtools/SDL2/SDL2-2.0.12/lib/x86/SDL2main.lib(Win32/Release/SDL_windows_main.obj):(.text[_main_getcmdline]+0xd1): undefined reference to `SDL_main'
collect2.exe: error: ld returned 1 exit status
CMakeFiles\Vivaria.dir\build.make:104: recipe for target 'Vivaria.exe' failed
mingw32-make[2]: *** [Vivaria.exe] Error 1
CMakeFiles\Makefile2:91: recipe for target 'CMakeFiles/Vivaria.dir/all' failed
mingw32-make[1]: *** [CMakeFiles/Vivaria.dir/all] Error 2
Makefile:99: recipe for target 'all' failed
mingw32-make: *** [all] Error 2

install_buildtools_windows.bat

set SDL2=SDL2-devel-2.0.12-VC.zip
set DOWNLOAD_DIR=%cd%\buildtools
set OUTPUT_DIR=%cd%\buildtools\SDL2

wget "https://libsdl.org/release/%SDL2%" -P "%DOWNLOAD_DIR%"

7z x "%DOWNLOAD_DIR%\%SDL2%" -y -o%OUTPUT_DIR%

del /F /Q %DOWNLOAD_DIR%\%SDL2%

As you can see I'm still "a bit" new to CMake, but I'm trying to learn.

Answer 1

Oof. Everything about your CMakeLists is wrong.

1. Never set CMAKE_CXX_FLAGS in your CMakeLists.txt
2. Never use include_directories or link_directories
3. Never use target_link_libraries without a visibility specifier.
4. Never set paths to libs manually.
5. Don't set your target names equal to the project name. It's pointless complexity and bad style.

This is all you need:

cmake_minimum_required(VERSION 3.16)
project(Vivaria VERSION 1.0.0)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED YES)
set(CMAKE_CXX_EXTENSIONS OFF)

find_package(SDL2 REQUIRED)

add_executable(Vivaria vivaria.cpp)
target_link_libraries(Vivaria PRIVATE SDL2::SDL2)

Your code also has an error. You need to add this line to the top of your file

#define SDL_MAIN_HANDLED

First, use vcpkg to install SDL2. Then, with the above changes, this compiles and runs for me using the commands:

> mkdir build
> cd build
> cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=X:/path/to/vcpkg.cmake ..

Answer 2

Thanks to Tsyvarev! Setting the macro SDL_MAIN_HANDLED in the source file fixed the problem.

#define SDL_MAIN_HANDLED // insert this
#include <iostream>
#include "SDL.h"

int main() {
    if (SDL_Init(SDL_INIT_VIDEO) != 0){
        std::cout << "Hello world" << std::endl;
        return 1;
    }
    
        std::cout << "Hello world 2" << std::endl;

    SDL_Quit();
    return 0;
}