Objective-C如何处理不可变字符串的内存 [英] How Objective-C handles the memory of immutable strings

问题描述

在我的研究中，我遇到了一些奇怪的事情.

In my research I've come across something peculiar.

@interface Class {
    NSString *_string
}

- (void) Method1 {
    _string = @"ASDF";
}

最初，我认为_string是自动释放池的一部分，实际上并没有考虑它的内存方面.

Intially I thought that _string was part of the autorelease pools and really didn't think about the memory aspect of it.

在阅读此SO帖子后客观C NSString *属性保留计数奇数 我已经意识到不可以，_string的保留计数实际上是UINT_MAX

After reading this SO post Objective C NSString* property retain count oddity I've realized that no, this is not the case, and that the retain count of _string is actually UINT_MAX

很显然，我认为_string是自动释放池的一部分，这是fl幸，而且我以某种方式解决了如何处理变量的问题.但是，我想知道的是:@"ASDF"什么时候被扔掉的?我知道我应该使用属性和设置器，但是可能有很多代码看起来像这样，因为将常量分配给变量非常直观.

Obviously my thinking that _string was part of the autorelease pool was a fluke, and how I handled the variable just somehow worked out. What I would like to know, though, is: when does @"ASDF" get thrown away? I know I should be using properties and setters, but there is probably a lot of code out there that looks like this since assigning a constant to a variable is so intuitive.

这些不可变的文字NSString的生命周期是什么?由于@"ASDF"不再驻留在内存中，[_string length]何时会真正返回错误?

What is the lifecycle of these immutable, literal NSStrings, and when will [_string length] actually return an error since @"ASDF" doesn't reside in memory anymore?

推荐答案

来自是原义的NSString自动发布还是需要发布?

由编译器分配的字符串(格式为"STRING")是常量，并且 因此-retain，-release和-autorelease消息将被忽略. 在这种情况下，您不必释放或自动释放foo(但是 不会受伤).

Compiler allocated strings (of the format @"STRING") are constant, and so -retain, -release, and -autorelease messages to them are ignored. You don't have to release or autorelease foo in this case (but it won't hurt).

当你这样做的时候，在幕后

Under the hood when you do

NSString* yourString = @"ABC";

该字符串将存储在称为数据段的内存区域中.启动应用程序后，该区域永远不会改变.在这里，字符串被视为应用程序的常量.同时，字符串是一个对象，因此，如果要保留它，请调用retain或copy.

the string will be stored in a area of memory called data segment. This area never changes after the application is launched. Here strings are treated as constants for your app. At the same time a string is an object, so if you want to keep it you call retain or copy.

在竞争时

NSString* yourString = // alloc-init

您在堆上创建一个对象.如果忘记释放，则有内存泄漏.如果其他人破坏了它，并且您尝试访问它，则可能无法访问该内存位置.

you create an object on the heap. If you forget to release you have a memory leak. If someone else destroy it, and you try to access it, you have a bad access to that memory location.

希望有帮助.

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