/// header

id CGSCopyManagedDisplaySpaces(int conn);
int _CGSDefaultConnection();
id CGSCopyWindowsWithOptionsAndTags(int conn, unsigned owner, NSArray *spids, unsigned options, unsigned long long *setTags, unsigned long long *clearTags);


// code

int spaceNumber = 0;  // the space you want to get the windows for. numbering starts at 0.

int conn = _CGSDefaultConnection();
NSArray *info = CGSCopyManagedDisplaySpaces(conn);
NSLog(@"space info: %@", info);
unsigned long long setTags = 0, clearTags = 0x4000000000;
int displayNumber = 0;
NSNumber *spaceID = info[displayNumber][@"Spaces"][spaceNumber][@"id64"];
NSArray *windows = CGSCopyWindowsWithOptionsAndTags(conn, 0, @[spaceID], 2, &setTags, &clearTags);
NSLog(@"windows on space %d are %@", spaceNumber, windows);