c++ - 获取指向结构的第一个元素的指针

Question

我认为该标准为我提供了一个函数来查找结构的第一个^st 元素。不过我好像找不到。

我害怕对齐:我认为将 reinterpret_cast 放入结构的第 1^st 元素中是不合法的，对吗？

例如给定 struct { int first, int second } foo;如果我不知道 first 被布置为 1<支持>st 元素？ (这意味着 &foo.first 不是有效的解决方案。)

Answer 1

I don't think it's legal to reinterpret_cast into the 1st element of a struct is it?

它是合法的，但前提是该类是标准布局。标准草案:

[basic.compound]

Two objects a and b are pointer-interconvertible if:

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• one is a standard-layout class object and the other is the first non-static data member of that object, or, if the object has no non-static data members, any base class subobject of that object (10.3), or

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If two objects are pointer-interconvertible, then they have the same address, and it is possible to obtain a pointer to one from a pointer to the other via a reinterpret_cast ...