这里记录下NSMutableData的使用，当我们用到socket传送信息时，要将数据转换成数据流。这时就用NSData

下面举个小例子，说明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 = @"随便写的什么呢？";
     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);