Added some extra protection to notify the developer if they haven't initialized the application properly.

This will help reduce issues like that reported in bug 1819:

Wouter van Oortmerssen 2013-04-23 20:12:07 EDT
#0  0x01d1e881 in __HALT ()
#1  0x01c58971 in _CFRuntimeCreateInstance ()
#2  0x02e4acc1 in GSFontCreateWithName ()
#3  0x00adc0e1 in UINewFont ()
#4  0x00adc24c in +[UIFont systemFontOfSize:traits:] ()
#5  0x00adc298 in +[UIFont systemFontOfSize:] ()
#6  0x009fb5d9 in +[UITextFieldLabel defaultFont] ()
#7  0x00a8ccd5 in -[UILabel _commonInit] ()
#8  0x00a8ce14 in -[UILabel initWithFrame:] ()
#9  0x00a052eb in -[UITextField createTextLabelWithTextColor:] ()
#10 0x009fbede in -[UITextField initWithFrame:] ()
#11 0x00152ead in -[SDL_uikitview initializeKeyboard] at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitview.m:208
#12 0x0015290c in -[SDL_uikitview initWithFrame:] at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitview.m:50
#13 0x00153b5b in -[SDL_uikitopenglview initWithFrame:scale:retainBacking:rBits:gBits:bBits:aBits:depthBits:stencilBits:majorVersion:] at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitopenglview.m:53
#14 0x001524ff in UIKit_GL_CreateContext at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/uikit/SDL_uikitopengles.m:114
#15 0x0015078f in SDL_GL_CreateContext at /Users/aardappel/lobster/external/SDL-2.0.0-7046/Xcode-iOS/SDL/../../src/video/SDL_video.c:2666
#16 0x000d8c5c in SDLInit(char const*, vec<int, 2>&) at /Users/aardappel/lobster/dev/xcode/lobster/../../src/sdlsystem.cpp:193

include/SDL_main.h

@@ -72,6 +72,15 @@ extern C_LINKAGE int SDL_main(int argc, char *argv[]);
 extern "C" {
 #endif
 
+/*
+ *  This is called by the real SDL main function to let the rest of the
+ *  library know that initialization was done properly.
+ *
+ *  Calling this yourself without knowing what you're doing can cause
+ *  crashes and hard to diagnose problems with your application.
+ */
+extern DECLSPEC void SDL_SetMainReady(void);
+
 #ifdef __WIN32__
 
 /**

src/SDL.c

@@ -43,6 +43,11 @@ extern int SDL_HelperWindowDestroy(void);
 
 
 /* The initialized subsystems */
+#ifdef SDL_MAIN_NEEDED
+static SDL_bool SDL_MainIsReady = SDL_FALSE;
+#else
+static SDL_bool SDL_MainIsReady = SDL_TRUE;
+#endif
 static SDL_bool SDL_bInMainQuit = SDL_FALSE;
 static Uint8 SDL_SubsystemRefCount[ 32 ];
 
@@ -88,9 +93,20 @@ SDL_PrivateShouldQuitSubsystem(Uint32 subsystem) {
     return SDL_SubsystemRefCount[subsystem_index] == 1 || SDL_bInMainQuit;
 }
 
+void
+SDL_SetMainReady(void)
+{
+    SDL_MainIsReady = SDL_TRUE;
+}
+
 int
 SDL_InitSubSystem(Uint32 flags)
 {
+    if (!SDL_MainIsReady) {
+        SDL_SetError("Application didn't initialize properly, did you include SDL_main.h in the file containing your main() function?");
+        return -1;
+    }
+
 #if !SDL_TIMERS_DISABLED
     SDL_InitTicks();
 #endif

src/main/android/SDL_android_main.cpp

@@ -20,6 +20,8 @@ extern "C" void Java_org_libsdl_app_SDLActivity_nativeInit(JNIEnv* env, jclass c
     /* This interface could expand with ABI negotiation, calbacks, etc. */
     SDL_Android_Init(env, cls);
 
+    SDL_SetMainReady();
+
     /* Run the application code! */
     int status;
     char *argv[2];

src/main/psp/SDL_psp_main.c

@@ -37,8 +37,6 @@
    PSP_MAIN_THREAD_STACK_SIZE, etc.
 */
 
-extern int SDL_main(int argc, char *argv[]);
-
 PSP_MODULE_INFO("SDL App", 0, 1, 1);
 
 int sdl_psp_exit_callback(int arg1, int arg2, void *common)
@@ -75,6 +73,8 @@ int main(int argc, char *argv[])
     /* Register sceKernelExitGame() to be called when we exit */
     atexit(sceKernelExitGame);
 
+    SDL_SetMainReady();
+
     (void)SDL_main(argc, argv);
     return 0;
 }

src/main/windows/SDL_windows_main.c

@@ -134,6 +134,8 @@ console_main(int argc, char *argv[])
 {
     int status;
 
+    SDL_SetMainReady();
+
     /* Run the application main() code */
     status = SDL_main(argc, argv);
 

src/video/uikit/SDL_uikitappdelegate.m

@@ -37,7 +37,6 @@
 #undef main
 #endif
 
-extern int SDL_main(int argc, char *argv[]);
 static int forward_argc;
 static char **forward_argv;
 static int exit_status;
@@ -187,6 +186,8 @@ static void SDL_IdleTimerDisabledChanged(const char *name, const char *oldValue,
 
 - (void)postFinishLaunch
 {
+    SDL_SetMainReady();
+
     /* run the user's application, passing argc and argv */
     SDL_iPhoneSetEventPump(SDL_TRUE);
     exit_status = SDL_main(forward_argc, forward_argv);