如何替换 char 数组中的 char？ Xcode

Question

我在 Objective-C (Xcode):

中得到以下 char 数组

char *incomeMessage;


NSString *str = [[NSString alloc] initWithBytes:data.bytes length:data.length encoding:NSUTF8StringEncoding];
incomeMessage = [str UTF8String];

NSLog(@"%c", incomeMessage[0]);
NSLog(@"%c", incomeMessage[1]);
NSLog(@"%c", incomeMessage[2]);
NSLog(@"%c", incomeMessage[3]);
NSLog(@"%c", incomeMessage[4]);
NSLog(@"%c", incomeMessage[5]);

例如，我在控制台中得到了这样的结果：

现在我想将 incomeMessage[2] 中的字符替换为 4:

incomeMessage[2] = '4';

但是它给了我错误： EXC_BAD_ACCESS

你有什么想法，如何解决这个问题？

Answer 1

i got the following char array in Objective-C (Xcode)

你不知道，你知道的。你所拥有的只是一个指针。你没有留出任何实际的记忆；那里没有数组。

incomeMessage = [str UTF8String];

您在该行中所做的只是将指针 incomeMessage 重新指向字符串的 UTF8String。字符串的 UTF8String 是不可变的。请注意文档中的这段话：

you should copy the C string if it needs to be stored outside of the memory context in which you use this property.

所以基本上，如果你想写入 char 的数组，你的首要任务应该是制作一个 char 的数组。

Answer 2

根据 reference documentation，UTF8String returns 对字符串数据的只读 (const char*) 引用。

参考文献 material 继续说明：

This C string is a pointer to a structure inside the string object, which may have a lifetime shorter than the string object and will certainly not have a longer lifetime. Therefore, you should copy the C string if it needs to be stored outside of the memory context in which you use this property.

所以我建议听从他们的建议并创建数组的副本，然后对其进行修改。

例如：http://ideone.com/mhjwZW

你可能会更幸运，比如：

NSString* str = [[NSString alloc] initWithBytes:data.bytes length:data.length encoding:NSUTF8StringEncoding];
char* incomeMessage = malloc([str lengthOfBytesUsingEncoding:NSUTF8StringEncoding] + 1);
strcpy(incomeMessage, [str UTF8String]);

//now you can change things    
incomeMessage[2] = '4';

//do this when you're done
free(incomeMessage);

尽管如此，您是否有任何特殊原因想要使用 C-string/character 数组而不是 NSMutableString？我想你可能会发现 replaceCharactersInRange:withString: a better approach generally. See also: stringByReplacingCharactersInRange:withString:.

如何替换 char 数组中的 char？ Xcode

How to replace a char in an an char array? Xcode

arrays

exc-bad-access

objective-c

char