“_”之间的区别是什么？和“__”在Objective-C？ [英] What's the difference between "_" and "__" in Objective-C?

问题描述

我已经读过， _ （下划线）仅用于告诉变量/方法/类是仅供API使用，不应该被其他

I've read that _ (underscore) is only used to tell that the variable/method/class is for the API use only and should not be used by other programmers.

__ （双下划线）？

在此示例中 __ block BOOL found = NO;

。

From the Apple Docs about Block Objects.

此外，任何人都可以帮助我理解指针到指针的概念？
** var
我读了一些关于它的答案，但没有真正得到它。

Also, can anyone help me understand the concept of pointer-to-pointers? **var I've read some answers about it but didn't really get it. When and how should I use it?

推荐答案

单下划线传统上用于私有API（方法，有时是ivars）。它们的主要目的是防止名称冲突。

Single underscore is traditionally used for private API (methods and sometimes ivars). Their main purpose is to prevent name collisions.

__ block 是新块API的关键字。

__block is a keyword for the new blocks API. In general, double underscore keywords are for the compiler.

对于指针的指针， NSError 就是一个很好的例子：当一个方法想要返回一个新的 NSError 对象作为其参数（不是返回值）的一部分时，您需要一个指向 NSError * ，以便您可以分配它。有了一个简单的指针，你只能访问对象，但不能（重新）分配。

For pointers to pointers the NSError is a good example: When a method wants to return a new NSError object as part of its parameters (not return value), you need a pointer to a variable of type NSError *, so that you can assign it. With a simple pointer you could only access the object, but not (re-)assign it.

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