问题描述
示例： NSSagedObjectContext 的 -save：方法声明如下：
Example: The -save: method of NSManagedObjectContext is declared like this:
- (BOOL)save:(NSError **)error
由于NSError已经是一个类，并且传递一个指针实际上会在 -save：的实现中修改这个对象的效果，那是什么将指针传递给指针的重点是什么？什么是优势/意义？
Since NSError is already a class, and passing a pointer would actually have the effect of modifying this object inside the implementation of -save:, what's the point of passing a pointer to a pointer here? What's the advantage/sense?
用法示例：
NSError *error;
if (![managedObjectContext save:&error]) {
// Handle the error.
}
推荐答案
如果你刚刚通过指针，所有方法都可以改变你指向的已经存在的NSError对象。
If you just passed in a pointer, all the method could do would alter the already existing NSError object that you are pointing to.
通过传入一个指向指针的指针，它可以创建新的NSError对象并留下指向它们的指针。
By passing in a pointer to a pointer, it can create new NSError objects and leave you with a pointer that points to them.
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