Programmatically read and change the brightness on macOS

changeMacBrightness.m

#import <Foundation/Foundation.h>
#import <IOKit/IOKitLib.h>
#import <IOKit/graphics/IOGraphicsLib.h>

// this helped me out a lot <3: https://stackoverflow.com/questions/3239749/programmatically-change-mac-display-brightness

int main(int argc, char *argv[]) {
	io_iterator_t iterator;
	kern_return_t result = IOServiceGetMatchingServices(kIOMasterPortDefault, IOServiceMatching("IODisplayConnect"), &iterator);
													
	// If we were successful
	if (result == kIOReturnSuccess)
	{
		io_object_t service;
		while ((service = IOIteratorNext(iterator))) {
			// Print the current brightness of the screen
			float current_brightness;
			IODisplayGetFloatParameter(service, kNilOptions, CFSTR(kIODisplayBrightnessKey), &current_brightness);
			printf("current brightness: %.0f%%\n", current_brightness * 100);

			// Set the custom brightness of the screen
			float custom_brightness = 0.69; /* this value controls the screen brightness with
											0 being minimum brightness and 1 being maximum brightness */
			IODisplaySetFloatParameter(service, kNilOptions, CFSTR(kIODisplayBrightnessKey), custom_brightness);
			
			// Print the custom brightness of the screen
			IODisplayGetFloatParameter(service, kNilOptions, CFSTR(kIODisplayBrightnessKey),
												&custom_brightness);
			printf("new custom brightness: %.0f%%\n", custom_brightness * 100);

			// Let the object go
			IOObjectRelease(service);
			return 0;
		}
	}
}