In MacOSX, when drag'n'dropping a document on an SDL app, or double-clicking a document associated with the app, the document(s) are passed to SDL_main() as if they were command line arguments. Otherwise, the command line is always empty and there is no way for the app to recover this information.

/* Include the SDL main definition header */
#include "SDL_main.h"

#ifdef main
#undef main
int main(int argc, char *argv[])
{
	return(SDL_main(argc, argv));
}
#else
/* Nothing to do on this platform */;
#endif