enumerate displays using CGGetActiveDisplayList

gistfile1.m

    CGDirectDisplayID displays[MAX_DISPLAYS];
    uint32_t numDisplays;
    uint32_t i;
    
    CGGetActiveDisplayList(MAX_DISPLAYS, displays, &numDisplays);
    
    for(i=0; i<numDisplays; i++)
    {
        CGDisplayModeRef mode;
        CFIndex index, count;
        CFArrayRef modeList;
        
        modeList=CGDisplayCopyAllDisplayModes(displays[i], NULL);
        count=CFArrayGetCount(modeList);
        
        NSLog(@"\n\nmode --");
        
        for(index=0;index<count;index++)
        {
            mode=(CGDisplayModeRef)CFArrayGetValueAtIndex(modeList, index);
            
            long h=0, w=0;
            h=CGDisplayModeGetHeight(mode);
            w=CGDisplayModeGetWidth(mode);
            
            uint32_t flags=CGDisplayModeGetIOFlags(mode);
            NSLog(@"flags: %d", flags);
            
            NSLog(@"w, h: %ld, %ld", w, h);
            
            //test mode here against required params and set, using:
            //CGDisplaySetDisplayMode(displays[i], mode, NULL);
        }
        
        CFRelease(modeList);
    }

Based pretty much entirely on the Quartz Display Services doc here https://developer.apple.com/library/mac/#documentation/graphicsimaging/Conceptual/QuartzDisplayServicesConceptual/Articles/DisplayModes.html#//apple_ref/doc/uid/TP40004234-SW1