Imgui can not find SDL3/SDL.h file

Question

I am trying to learn imgui by first create a project using its library. But, first I wanted to run one of the examples found in the github repository. I am not using an IDE, only my mac terminal. Therefore, I am using cmake to build the project. Here is my project directory structure:

imgui_project
    |____build
    |____CMakeLists.txt
    |____src
    |     |__CMakeLists.txt
    |     |__main.cpp
    |____Vendors
          |___CMakeLists.txt
          |___Imgui
          |     |____CMakeLists.txt
          |___sdl
                |____CMakeLists.txt

The content in the files:

imgui_project/CMakeLists.txt

cmake_minimum_required(VERSION 3.22)
project(imgui_app)
add_subdirectory(vendors)
add_subdirectory(src)

src/CMakeLists.txt

set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
add_executable(myapp main.cpp)
target_link_libraries(myapp PRIVATE SDL3 imgui)

src/main.cpp

{the entire content of example_sdl3_renderer3 main.cpp file from the imgui github repository.}

Vendors/CMakeLists.txt

add_subdirectory(sdl)
add_subdirectory(imgui)

Vendors/imgui/CMakeLists.txt

include(FetchContent)

FetchContent_Declare(
    imgui
    GIT_REPOSITORY https://github.com/ocornut/imgui.git
    GIT_TAG docking
)
FetchContent_MakeAvailable(imgui)
add_library(imgui)
target_include_directories(
    imgui
    PUBLIC 
    ${imgui_SOURCE_DIR}
    ${imgui_SOURCE_DIR}/backends
)
target_sources(
    imgui
    PUBLIC 
    ${imgui_SOURCE_DIR}/imgui.cpp
    ${imgui_SOURCE_DIR}/imgui_draw.cpp
    ${imgui_SOURCE_DIR}/imgui_demo.cpp
    ${imgui_SOURCE_DIR}/imgui_tables.cpp
    ${imgui_SOURCE_DIR}/imgui_widgets.cpp
    ${imgui_SOURCE_DIR}/backends/imgui_impl_sdl3.cpp
    ${imgui_SOURCE_DIR}/backends/imgui_impl_sdlrenderer3.cpp
)
target_link_directories(imgui PUBLIC SDL3)

Vendors/sdl/CMakeLists.txt

include(FetchContent)
FetchContent_Declare(
    SDL3
    GIT_REPOSITORY https://github.com/libsdl-org/SDL.git
    GIT_TAG release-3.2.20
)
FetchContent_MakeAvailable(SDL3)

I build the project in the build directory using the command: cmake .. -G "Unix Makefiles"
When I run make, the error I am getting:

.../imgui_project/build/_deps/imgui-src/backends/imgui_impl_sdl3.cpp:83:10: fatal error: 'SDL3/SDl.h' file not found
83 | #include <SDL3/SDL.h>

In the SDL3 github repository, 3.2.20 release, in the include/SDl3/ directory, SDL.h is there. I thought having the FetchContent_MakeAvailable(SDL3) would make the library available in the build after fetching it. So, I am not sure why it is not able to find the SDL.h file. That is the only error I am currently getting.

@AhmedAEK I had it SDL3::SDL3 before, when I kept getting the error , I tried a few things, and end up leaving SDL3 when I posted this question. — Charles Florestal
– Charles Florestal, Commented Aug 18 at 17:35
You may want to enable verbose make with make VERBOSE=1 to see what exact include directories are being used after you fix it back to: target_link_directories(imgui PUBLIC SDL3::SDL3) which is correct. — drescherjm
– drescherjm, Commented Aug 18 at 19:12
@drescherjm I fixed the text back to SDL3::SDL3 and after rebuilding cmake in the build directory, I ran the make VERBOSE=1. I am not sure what I should be looking for. I took a look into the build directory after cmake .. -G "Unix Makefiles" command ,before make, to see if a copy of the SDL.h was made. I found it in build/_deps/sdl3_src/include/SDL3/ path. After entering make command, the process Building CXX object.....imgui_impl_sdl3.cpp.o prior to the error doesn't refer to that path at all, in any of the verbose output text provided. What should I be looking for exactly? — Charles Florestal
– Charles Florestal, Commented Aug 18 at 21:20
I expected it to show the full build command on each file so you could see what parameters are passed to g++ to see if -Ibuild/_deps/sdl3_src/include was added when building your imgui code. — drescherjm
– drescherjm, Commented Aug 18 at 22:46

Charles Florestal · Accepted Answer · 2025-08-21 02:27:28Z

1

The build system generates the SDL3 library in the build folder, but imgui was not searching in the correct directory due to the command issue. target_link_directories(imgui PUBLIC SDL3) in the vendors/imgui/CMakeLists.txt file, on the last line, needs to be target_link_libraries(imgui PUBLIC SDL3::SDL3).

answered Aug 21 at 2:27

Charles Florestal

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