程式碼：

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    
    NSString *birthDay=[self birthdayStrFromIdentityCard:@"134825194401014241"];
    NSLog(@"--birthDay-%@",birthDay);
    
}
//傳身份證返回生日字串
-(NSString *)birthdayStrFromIdentityCard:(NSString *)numberStr{
    
    NSMutableString 
 
*result = [NSMutableString stringWithCapacity:0];
    NSString *year = nil;
    NSString *month = nil;
    
    BOOL isAllNumber = YES;
    NSString *day = nil;
    if([numberStr length]<14)
        return result;
    
    //**擷取前14位
    NSString *fontNumer = [numberStr substringWithRange:NSMakeRange(0
 
, 13)];
    
    //**檢測前14位否全都是數字;
    const char *str = [fontNumer UTF8String];
    const char *p = str;
    while (*p!='\0') {
        if(!(*p>='0'&&*p<='9'))
            isAllNumber = NO;
        p++;
    }
    
    if(!isAllNumber)
        return result;
    
    year = [numberStr substringWithRange:NSMakeRange(6
 
, 4)];
    month = [numberStr substringWithRange:NSMakeRange(10, 2)];
    day = [numberStr substringWithRange:NSMakeRange(12,2)];
    
    [result appendString:year];
    [result appendString:@"-"];
    [result appendString:month];
    [result appendString:@"-"];
    [result appendString:day];
    return result;
    
}

輸出:

2015-10-13 13:26:38.308 傳身份證號碼可返回生日字串[6947:172533] --birthDay-1944-01-01