Set an error message to be retrieved with SDLNet_GetError.
void SDLNet_SetError(const char *fmt, ...);
a printf-style format string for the error message.
Generally you don't need to call this (SDL_net will use it internally to report errors), but it could be useful if you need to inject an error message of your own in here.
This function is available since SDL_net 2.0.0.