title: Why SDL_Window is an incomplete type?
body: <p>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</p>
  
  <pre><code>error: invalid use of incomplete type 'SDL_Window {aka struct SDL_Window}'
  </code></pre>
  
  <p>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:</p>
  
  <pre><code>ndk-build NDK_PROJECT_PATH=. APP_BUILD_SCRIPT=./Android.mk APP_PLATFORM=android-18
  </code></pre>
  
  <p>Then, I have copied the freshly built <code>libSDL2.so</code> into <code>$ANDROID_TOOLCHAIN/sysroot/usr/lib</code> and the files in the <code>include/</code> directory in <code>$ANDROID_TOOLCHAIN/sysroot/usr/include/SDL</code>. 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.</p>
  
  <p>I did a quick search in SDL's source code and found that <code>SDL.h</code> includes <code>SDL_video.h</code> which contains a typedef <code>SDL_Window</code> on <code>struct SDL_Window</code>. Then I searched for this struct and did not find anything except in the original source archive, in a file named <code>src/video/SDL_sysvideo.h</code>. Since it is not a file of the API, I doubt I have to include it in my code.</p>
  
  <p>So, how to find a definition of SDL_Window in SDL2, for Android (if this is relevant)?</p>