“NSString stringWithUTF8String：”是过度触摸 [英] "NSString stringWithUTF8String:" is overly touchy

问题描述

我正在使用高级Cocoa功能，如 NSString 和 NSData 而不是挖掘C级的东西，比如工作在 char 的数组。

I'm in the middle of doing some string manipulation using high-level Cocoa features like NSString and NSData as opposed to digging down to C-level things like working on arrays of chars.

它， + [NSString stringWithUTF8String：] 有时会在一个完美的字符串中返回 nil c> - [NSString UTF8String] 。可以假定当输入格式错误时会发生这种情况。下面是十六进制输入失败的示例：

For the love of it, +[NSString stringWithUTF8String:]sometimes returns nil on a perfectly good string that was created with -[NSString UTF8String] in the first place. One would assume that this happens when the input is malformed. Here is an example of the input that fails, in hex:

55 6B 66 51 35 59 4A 5C 6A 60 40 33 5F 45 58 60 9D 47 3F 6E 5E 
60 59 34 58 68 41 4B 61 4E 3F 41 46 00

和ASCII：

UkfQ5YJ\j`@3_EX`G?n^`Y4XhAKaN?AF

这是一个随机生成的字符串，用于测试我的子程序。

This is a randomly generated string, to test my subroutine.

char * buffer = [randomNSString UTF8String];
// .... doing things .... in the end, buffer is the same as before
NSString * result = [NSString stringWithUTF8String:buffer];
// yields nil

编辑：为了防止有人没有理解隐式问题，这里是-v模式：

Just in case somebody didn't grasp the implicit question, here it is in -v mode:

为什么[NSString stringWithUTF8String：]有时会返回 nil 对完美形成的UTF8-String？

Why does [NSString stringWithUTF8String:] sometimes return nil on a perfectly formed UTF8-String?

推荐答案

walkytalky是对的。 9d在utf8中不合法。具有顶部位10的utf8字节被保留为连续字符，它们不会出现没有前缀字符的多个前导位。

walkytalky is right. 9d is not legal in utf8 in this way. utf8 bytes with the top bits 10 are reserved as continuation characters, they never appear without a prefix character with more than one leading bit.

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