這裡記錄下NSMutableData的使用，當我們用到socket傳送信息時，要將數據轉換成數據流。這時就用NSData

下面舉個小例子，說明NSData的用法。

NSMutableData *mutableData = [[NSMutableData alloc] init];
    int i = 143;
    NSData *data = [NSData dataWithBytes:&i length:sizeof(i)];
    [mutableData appendData:data];
    
    
    NSString *str = @隨便寫的什麼呢？;
     NSData *data3 = [str dataUsingEncoding:NSUTF8StringEncoding];
    NSUInteger strlen = data3.length;
    
    
    NSData *data6 = [NSData dataWithBytes:&strlen length:sizeof(int)];
    [mutableData appendData:data6];
    
   
    [mutableData appendData:data3];
    
    
    int strlen1 = 0;
    
    [mutableData getBytes:&strlen1 range:NSMakeRange(4, sizeof(int))];
    
    NSData *strData = [mutableData subdataWithRange:NSMakeRange(8, strlen1)];;
  
    NSString *string1 = [[NSString alloc] initWithData:strData encoding:NSUTF8StringEncoding];
    
    NSLog(@%@,string1);