Why SDL_Window is an incomplete type?

问题

I am porting to SDL2 and the Android platform a C++ game that uses SDL 1.2. Everything went well so far except for one thing: when I try to access the fields of SDL_Window, the compiler tells me

error: invalid use of incomplete type 'SDL_Window {aka struct SDL_Window}'

I think my installation of SDL may be faulty. I have compiled SDL 2.0.0 from the source found on libsdl.org using the folloing command:

ndk-build NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=./Android.mk APP_PLATFORM=android-18

Then, I have copied the freshly built libSDL2.so into $ANDROID_TOOLCHAIN/sysroot/usr/lib and the files in the include/ directory in $ANDROID_TOOLCHAIN/sysroot/usr/include/SDL. These files are given to CMake and referenced by the game's code. I managed to convert every SDL calls and now I am stuck with this SDL_Window problem.

I did a quick search in SDL's source code and found that SDL.h includes SDL_video.h which contains a typedef SDL_Window on struct SDL_Window. Then I searched for this struct and did not find anything except in the original source archive, in a file named src/video/SDL_sysvideo.h. Since it is not a file of the API, I doubt I have to include it in my code.

So, how to find a definition of SDL_Window in SDL2, for Android (if this is relevant)?

回答1:

It appears that the problem is a lack of knowledge of SDL 2's API. Let's remember that one does not access the fields of struct SDL_Window: there are functions to get the size and the flags of the window, such as SDL_GetWindowFlags and SDL_GetWindowSize.

So the problem is absolutely not related to the installation of the SDL or to Android builds. Sorry for the waste of time, people of the Web.

回答2:

I would expect that you are expected to only deal in pointers to SDL_Window objects, and not actually put a full SDL_Window object on the stack.

来源：https://stackoverflow.com/questions/18453393/why-sdl-window-is-an-incomplete-type