#import <Cocoa/Cocoa.h>
#import <objc/message.h>

NSRect foo (id screen)
{
    return ((NSRect (*)(id, SEL))objc_msgSend_stret)(screen, sel_registerName("visibleFrame"));
}

int main (int argc, const char** argv)
{
    Class cls = objc_getClass("NSScreen");
    id screen = ((id (*)(id, SEL))objc_msgSend)(cls, sel_registerName("mainScreen"));
    NSRect frame = foo(screen);

    printf("x=%f y=%f width=%f height=%f\n", frame.origin.x, frame.origin.y, frame.size.width, frame.size.height);
    return 0;
}