Why does SDL_NumJoysticks() never update?

Question

I was writing a small program in C that utilizes SDL 2.0, and ran into a problem when I couldn't get SDL_NumJoysticks() to report the number of joysticks plugged in at the time of the function call. I believe that it is reporting the number of joysticks connected during one of SDL's initialization functions (I would guess 'SDL_Init()', but I have no evidence), and then keeps on giving you that number throughout the rest of the program. Here is a short test program that I have been using:

#include <stdio.h>
#include <SDL2/SDL.h>

int main() {
    SDL_Event event;
    SDL_Window *window;
    short joysticks = 0;

    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_JOYSTICK) < 0) {
        fprintf(stderr, "SDL_Init error: %s\n", SDL_GetError());
        return 1;
    }

    window = SDL_CreateWindow("Test window", 0, 0, 800, 600, SDL_WINDOW_SHOWN);
    if (window == NULL) {
        fprintf(stderr, "SDL_CreateWindow error: %s\n", SDL_GetError());
        return 1;
    }

    printf("%s\n", SDL_GetError());

    while (1) {
        while (SDL_PollEvent(&event)) {
            if (event.type == SDL_QUIT) {
                printf("%s\n", SDL_GetError());
                SDL_DestroyWindow(window);
                SDL_Quit();
                return 0;
            } else if (event.type == SDL_JOYDEVICEADDED) {
                printf("Joystick added!\n");
            } else if (event.type == SDL_JOYDEVICEREMOVED) {
                printf("Joystick removed!\n");
            }
        }

        if (SDL_NumJoysticks() > joysticks) {
            printf("Joystick inserted.\n");
            joysticks++;
        } else if (SDL_NumJoysticks() < joysticks && SDL_NumJoysticks() >= 0) {
            printf("Joystick removed.\n");
            joysticks--;
        } else if (SDL_NumJoysticks() < 0) {
            printf("Something went wrong!\n");
            SDL_DestroyWindow(window);
            SDL_Quit();
            return 1;
        }
    }

    return 0;
}

The program accurately reports the number of joysticks plugged in when the program is started, but does absolutely nothing after that.

The official SDL docs for SDL_Numjoysticks() state that it "Returns the number of attached joysticks on success". How can I get it to tell me the number of joysticks plugged in at the time of the function call? Am I making a mistake in my code, or is that just not the way that SDL_NumJoysticks() works?

Answer 1

Make sure you follow these steps and see if you still have problems:

• Call SDL_JoystickEventState(SDL_ENABLE) after SDL_INIT
• If that is not enough, try to force an update by calling SDL_JoystickUpdate(); before while (SDL_PollEvent(&event))

EDIT: More info that I think should be useful:

• Always call SDL_PollEvent on the Main Thread (Or SDL_PumpEvents() on Main Thread and SDL_PeepEvents elsewhere)
• If you dont do that, SDL wont update the number of joysticks nor hotplug events
• Other joystick events work when you pump outside the Main thread but it is not recommended.