如何附加nsdata [英] how append nsdata

问题描述

我可以附加nsdata，我会附加长度数据在第一个消息发送在套接字
i使用这样的代码，但运行错误。

how i could append nsdata, i would append lenght data on first message to send on socket i use code like this but error on runing.

int lendata = [message length];
NSData *firstdata = [NSData dataWithBytes: &lendata length: sizeof(lendata)];
NSData *mdata = [message dataUsingEncoding:NSUTF8StringEncoding];
NSMutableData *seconddata = [NSData dataWithData:mdata];
[firstdata appendData:secondata];

请告诉我们是否有另一种方式
感谢您的帮助。

please tell if there is another way Thanks for your help.

推荐答案

看看我的水晶球：

1. 您正在将 seconddata 声明为 NSMutableData 实例，但随后使用 [NSData dataWithData：] 而不是 [NSMutableData dataWithData：]，因此 seconddata

1. You are declaring seconddata as an NSMutableData instance, but then you initialize it using [NSData dataWithData:] instead of [NSMutableData dataWithData:], so seconddata won't be mutable in the end and you cannot append to it.

您正试图附加到 firstdata

解决方案：make firstdata mutable：

Solution: make firstdata mutable:

NSMutableData *firstdata = [NSMutableData dataWithBytes: &lendata
                                                 length: sizeof(lendata)];
[firstData appendData:[message dataUsingEncoding:NSUTF8StringEncoding]];

然后你可以安全地删除 mdata code> seconddata ，因为它们不再需要了。

Then you can safely drop mdata and seconddata as they are not needed anymore.

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