Simple Example For Categories

NSDate+ComponentsExtractor.h:

 
typedef struct 
{
   NSInteger year;
   NSInteger month;
   NSInteger day;
} dateComponents;

@interface NSDate (ComponentsExtractor)
+ (dateComponents)componentsFromDate:(NSDate *)theDate;
@end

NSDate+ComponentsExtractor.m: 

#import "NSDate+ComponentsExtractor.h"

@implementation NSDate (ComponentsExtractor)

+ (dateComponents)componentsFromDate:(NSDate *)theDate
{
    NSCalendar *gregorian = [[[NSCalendar alloc] initWithCalendarIdentifier:

                                            NSGregorianCalendar] autorelease];
    unsigned unitFlags = NSYearCalendarUnit | NSMonthCalendarUnit | 

                                  NSDayCalendarUnit;
    NSDateComponents *components = [gregorian components:unitFlags 

                                          fromDate:theDate];
    
    dateComponents theComponents;
    theComponents.year = [components year];
    theComponents.month = [components month];
    theComponents.day = [components day];
    
    return theComponents;
}

@end

Making use of the category:

NSDate *theDate = [NSDate date]; // use the current date ...
dateComponents components = [NSDate componentsFromDate:theDate];
NSLog(@"%i - %i - %i", components.year, components.month, components.day);