Xcode を使ってQUITを押すと終了するプログラムを作ってみました。

#include <Carbon/Carbon.h>

#define BUTTON1 'BTN1'
pascal OSStatus MainWindowEventHandler(EventHandlerCallRef myHandler, EventRef event, void *userData) ;


pascal OSStatus MainWindowEventHandler(EventHandlerCallRef myHandler, EventRef event, void *userData)
{
    OSStatus   result = eventNotHandledErr ;
    HICommand  command ;

    GetEventParameter(
        event,
        kEventParamDirectObject,
        typeHICommand,
        NULL,
        sizeof (HICommand),
        NULL,
        &command
    ) ;

    switch (command.commandID)
    {
        case BUTTON1 :
            QuitApplicationEventLoop() ;
            break ;
    }

    return result;

}


int main(int argc, char* argv[])
{

    IBNibRef   nibRef ;
    WindowRef  window ;
    OSStatus   err ;

    EventTypeSpec mainSpec = {kEventClassCommand, kEventCommandProcess } ;

    err = CreateNibReference(CFSTR("main"), &nibRef) ;
    require_noerr(err, CantGetNibRef) ;

    err = SetMenuBarFromNib(nibRef, CFSTR("MenuBar")) ;
    require_noerr(err, CantSetMenuBar) ;

    err = CreateWindowFromNib(nibRef, CFSTR("MainWindow"), &window) ;
    require_noerr(err, CantCreateWindow) ;

    DisposeNibReference(nibRef) ;
    err = InstallWindowEventHandler(
        window,
        NewEventHandlerUPP(MainWindowEventHandler),
        1,
        &mainSpec,
        (void *)window,
        NULL
    ) ;
    ShowWindow(window) ;

    RunApplicationEventLoop() ;

CantCreateWindow:
CantSetMenuBar:
CantGetNibRef:

    return err ;

}