NSString 和 NSMutableString 有什么区别? [英] What is the difference between NSString and NSMutableString?

问题描述

我需要澄清一下 NSString 和 NSMutableString 之间的区别.任何人都可以简单地扩展一下吗?

I need a clarification regarding the difference between the NSString and NSMutableString. Can any one expand briefly?

推荐答案

假设你有这样的代码

NSString *s = [[NSString alloc] initWithString:@"Hello"];

s = [s stringByAppendingString:@"World"];

和其他类似的代码

NSMutableString *ms = [[NSMutableString alloc] initWithString:@"Hello"];

[ms appendString:@"World"];

从功能上讲，这两者都做同样的事情，除了一个区别 - 顶部代码块泄漏.-[NSString stringByAppendingString:] 生成一个新的不可变 NSString 对象，然后你告诉指针 s 指向它.但是，在此过程中，您孤立了 s 最初指向的 NSString 对象.如下更换线路将消除泄漏:

Both of these, functionally, do the same thing except for one difference - the top code block leaks. -[NSString stringByAppendingString:] generates a new immutable NSString object which you then tell the pointer s to point to. In the process, however, you orphan the NSString object that s originally pointed to. Replacing the line as follows would get rid of the leak:

s = [[s autorelease] stringByAppendingString:@"World"];

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