SDL_WasInit allows you to see which SDL subsytems have been initialized. flags is a bitwise OR'd combination of the subsystems you wish to check (see SDL_Init for a list of subsystem flags).
/* Here are several ways you can use SDL_WasInit() */
+
+/* Get init data on all the subsystems */
+Uint32 subsystem_init;
+
+subsystem_init=SDL_WasInit(SDL_INIT_EVERYTHING);
+
+if(subsystem_init&SDL_INIT_VIDEO)
+ printf("Video is initialized.\n");
+else
+ printf("Video is not initialized.\n");
+
+
+
+/* Just check for one specfic subsystem */
+
+if(SDL_WasInit(SDL_INIT_VIDEO)!=0)
+ printf("Video is initialized.\n");
+else
+ printf("Video is not initialized.\n");
+
+
+
+
+/* Check for two subsystems */
+
+Uint32 subsystem_mask=SDL_INIT_VIDEO|SDL_INIT_AUDIO;
+
+if(SDL_WasInit(subsystem_mask)==subsystem_mask)
+ printf("Video and Audio initialized.\n");
+else
+ printf("Video and Audio not initialized.\n");