objectivec中nil和NULL的区别

最新推荐文章于 2025-08-20 15:04:37 发布

gaco0722

最新推荐文章于 2025-08-20 15:04:37 发布

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文章标签： null java ie c

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47down voteaccepted

"nil" should only be used in place of an "id", what we Java and C++ programmers would think of as a pointer to an object. Use NULL for non-object pointers.

Look at the declaration of that method:

-(void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
change:(NSDictionary *)change context:(void *)context

context is a "void *" (ie a C-style pointer), so you'd definitely use NULL (which is sometimes declared as "(void *)0") rather than nil (which is of type "id").

而且与null不同，可以发送消息给nil。返回值还是一个nil。