NSDate Helper methods

1.To display time in relative time stamp use this method

-(NSString *)dateDiff:(NSString *)origDate {
    NSDateFormatter *df = [[NSDateFormatter alloc] init];
    [df setFormatterBehavior:NSDateFormatterBehavior10_4];
    [df setDateFormat:@"EEE, dd MMM yy HH:mm:ss VVVV"];
    NSDate *convertedDate = [df dateFromString:origDate];
    [df release];
    NSDate *todayDate = [NSDate date];
    double ti = [convertedDate timeIntervalSinceDate:todayDate];
    ti = ti * -1;
    if(ti < 1) {
     return @"never";
    } else  if (ti < 60) {
     return @"less than a minute ago";
    } else if (ti < 3600) {
     int diff = round(ti / 60);
     return [NSString stringWithFormat:@"%d minutes ago", diff];
    } else if (ti < 86400) {
     int diff = round(ti / 60 / 60);
     return[NSString stringWithFormat:@"%d hours ago", diff];
    } else if (ti < 2629743) {
     int diff = round(ti / 60 / 60 / 24);
     return[NSString stringWithFormat:@"%d days ago", diff];
    } else {
     return @"never";
    } 
}

2.If NSDateFormatter returns nil then use the below method to fix 

NSDateFormatter *parser = [[NSDateFormatter alloc] init];
[parser setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];