问题描述
我正在研究Steven Kochan的"Objective-C 2.0编程".我们创建了一个带有两个int实例变量的Fraction对象.在本书的后面，Kochan在一个分数对象的指针myFract上使用了sizeof语句:
I'm studying Steven Kochan's "Programming in Objective-C 2.0". We created a Fraction object with two int instance variables. Later in the book Kochan uses the sizeof statement on a Fraction object's pointer myFract:
sizeof(*myFract)
执行此操作时，出现编译错误:
When I do this, I receive a compile error:
http://clang.llvm.org/compatibility.html#sizeof-interface 指出，该对象的大小可以更改，但Fraction实例仅包含两个int实例变量(加上书中提到的继承的isa成员")时，可能会发生此错误.
http://clang.llvm.org/compatibility.html#sizeof-interface states this error could occur for an object who's size can change but a Fraction instance only contains the two int instance variables (plus an "inherited isa member" mentioned in the book).
我在做什么错了?
推荐答案
由于您使用的是现代ABI，因此对象的大小仍然可以更改.在旧版本的Objective-C中，对象基本上是结构，这意味着可以对它们进行sizeof()处理.情况已不再如此，从一开始它就从来不是一个特别好的主意.我不确定Kochan打算教什么，但是仅供参考，这对于编写Objective-C来说不是必需的.通过在Mac上将其构建为32位，您应该能够获得旧的行为，但是同样，在真正的程序中，这不是您想要做的.
The object's size could still change because you're using the modern ABI. In older versions of Objective-C, objects were basically structs and that meant it was possible to sizeof() them. This is no longer the case, and it was never a particularly good idea in the first place. I'm not sure what Kochan was trying to teach with it, but FYI this is not necessary to program Objective-C. You should be able to get the old behavior by building as 32-bit on the Mac, but again, that isn't something you'll want to do in real programs.
这篇关于“将'sizeof'无效应用到非脆弱ABI中的'Fraction'接口"在Objective-C中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！