Many users have complained to me that their joysticks are not detected in my SDL app when they run it under Windows. I did some research on this and i think i have found the problem:

At line 170 in SDL_mmjoystick.c it says:
  result = joyGetPosEx(SYS_JoystickID[i], &joyinfo);
but if you look closer at the code you see that SDL_JoystickID[i] is always zero. So for example when their joystick is assigned to the second position in the windows "driver" and the first position is empty, then it is never detected, because it always returns JOYERR_UNPLUGGED.

I believe this line should look like this:
  result = joyGetPosEx(i, &joyinfo);