read whether or not macOS's Do Not Disturb mode is on

dnd.c

#include <CoreFoundation/CoreFoundation.h>
#include <stdio.h>

int main()
{

  CFStringRef DO_NOT_DISTURB = CFStringCreateWithCString(kCFAllocatorDefault, "doNotDisturb", kCFStringEncodingUTF8);
  CFStringRef APP_ID = CFStringCreateWithCString(kCFAllocatorDefault, "com.apple.notificationcenterui", kCFStringEncodingUTF8);

  Boolean keyExists;
  Boolean result;

  result = CFPreferencesGetAppBooleanValue(DO_NOT_DISTURB, APP_ID, &keyExists);

  if (result)
  {
    printf("on\n");
  }
  else
  {
    printf("off\n");
  }

  return 0;
}