C but not used

Question

I use C to create bags. I get an error message parameter 'light_bitmap' set but not used [-Werror=unused-but-set-parameter]. However, the variable is used in my function. I am not sure what this message means. Below is the code I have:

In the header declaration:

void backlight_subscribe(GBitmap *light_bitmap, int start_hour, int end_hour);

In the definition of .c:

void backlight_subscribe(GBitmap *light_bitmap, int start_hour, int end_hour) {
    int hour = get_current_hour();
    if((hour >= start_hour) || (hour < end_hour)) {
        accel_tap_service_subscribe(tap_handler);
        light_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_LIGHT_ON_ICON);
    } else {
        accel_tap_service_unsubscribe();
        light_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_LIGHT_OFF_ICON);
    }
}

and in main.c:

static GBitmap *light_bitmap;
...
static void window_load(Window *window) {
     ...
     backlight_subscribe(light_bitmap, 22, 8);
     ...
}

static void init(void) {
    s_main_window = window_create();
    window_set_window_handlers(s_main_window, (WindowHandlers) {
        .load = window_load,
        .unload = window_unload,
    });
    window_stack_push(s_main_window, false); 
}

...

int main(void) {
    init();
    app_event_loop();
    deinit();
}

Full error message:

[16/28] c: src/accel_sensor.c -> build/src/accel_sensor.c.16.o
../src/accel_sensor.c: In function 'backlight_subscribe':
../src/accel_sensor.c:22:35: error: parameter 'light_bitmap' set but not used [-Werror=unused-but-set-parameter]
 void backlight_subscribe(GBitmap *light_bitmap, int start_hour, int end_hour) {
                                   ^
cc1: all warnings being treated as errors
Waf: Leaving directory `/home/adminuser/pebble/pebble-app/watchface/build'
Build failed

Can anyone see where I am doing wrong?

Answer 1

As the error says, in your function backlight_subscribeyou are assigning a value light_bitmap, but you are not reading it. This means that it is not used.

C . , , light_bitmap, . , , , , , , :

void backlight_subscribe(GBitmap **light_bitmap, int start_hour, int end_hour) {
    int hour = get_current_hour();
    if((hour >= start_hour) || (hour < end_hour)) {
        accel_tap_service_subscribe(tap_handler);
        *light_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_LIGHT_ON_ICON);
    } else {
        accel_tap_service_unsubscribe();
        *light_bitmap = gbitmap_create_with_resource(RESOURCE_ID_IMAGE_LIGHT_OFF_ICON);
    }
}

:

backlight_subscribe(&light_bitmap, 22, 8);

light_bitmap . , .