在 C++ 中，我可以从结构派生一个类吗
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in C++, can I derive a class from a struct
提问by SmacL
The question says it all really. Am I allowed derive a class from a struct, or should I create a class that embeds my struct and defines copy constructors and an = operator to move between the two?
问题说明了一切。我是否允许从结构派生一个类，还是应该创建一个嵌入我的结构并定义复制构造函数和 = 运算符以在两者之间移动的类？
回答by Alex B
In C++ structis (almost) synonymous to a class(except of different default access level), so yes, you can.
在 C++struct中（几乎）与 a 同义class（除了不同的默认访问级别），所以是的，你可以。
struct A {
// fields are public by default
};
class B: public A {
// fields are private by default
};
I'm not familiar with MFC, but it looks like an attempt to maintain both C and C++ APIs.
我不熟悉 MFC，但它看起来像是试图同时维护 C 和 C++ API。
回答by Johannes Schaub - litb
Of course you are. What is different regarding the inheritance is that if you define a class, it will inherit private from other classes/structs. If you define a struct and derive it from a class or struct, it will be a public inheritance by default:
你当然是。继承的不同之处在于，如果您定义一个类，它将从其他类/结构继承私有。如果你定义了一个结构体并从一个类或结构体派生出来，默认情况下它将是一个公共继承：
// the following two are equivalent except that one time class is
// used and the other time struct
struct f : g { };
class f : public g { };
If you wonder how you should wrap C structs - i would embed them as a member into the class. Because the C structs were not designed to be inherited from (think of the neither protected nor virtual destructor in the C structs - they can't have one). They are simple aggregates that collect data. And putting them as members uses them as such (as in "a point has a pair of an x and an y coordinate").
如果您想知道应该如何包装 C 结构 - 我会将它们作为成员嵌入到类中。因为 C 结构不是为了继承而设计的（想想 C 结构中既不是受保护的也不是虚拟的析构函数——它们不能有）。它们是收集数据的简单聚合。并将它们作为成员使用它们（例如“一个点具有一对 x 和一个 y 坐标”）。
C structs also expose members that possibly should not be exposed in the class. Containment allows precise control over what is exposed and what not by get/set functions and you can still let it give you a copy or reference to the contained naked C struct object.
C 结构还公开了可能不应在类中公开的成员。包含允许通过 get/set 函数精确控制公开的内容和不公开的内容，您仍然可以让它为您提供对包含的裸 C 结构对象的副本或引用。
回答by Stephen C. Steel
Yes. you can derive a class from a struct. In C++, a struct is simply a class where the default access is public rather than private. Deriving a class from a struct that only adds non-virual member functions and/or static functions is a useful technique to provide a C++ interface while maintaining compatability with a C style API.
是的。您可以从结构派生类。在 C++ 中，结构只是一个类，其中默认访问是公共的而不是私有的。从仅添加非虚拟成员函数和/或静态函数的结构派生类是一种有用的技术，可提供 C++ 接口，同时保持与 C 风格 API 的兼容性。
This is exactly the approach used by MFC for many of the C structs (contrary to what you state in your question).
这正是 MFC 用于许多 C 结构的方法（与您在问题中陈述的相反）。
For example, the CRect class is publicly derived from struct tagRECT (the more commonly used name RECT is a typededf for struct tagRECT). Because struct tagRECT defines all the data members, and CRect adds only non-virtual member functions, the memory layout of CRects and RECTs are identical - you can use a CRect as an argument for any function expected a RECT and vice-versa.
例如，CRect 类是从 struct tagRECT 公开派生的（更常用的名称 RECT 是 struct tagRECT 的 typededf）。因为 struct tagRECT 定义了所有数据成员，而 CRect 只添加了非虚拟成员函数，所以 CRect 和 RECT 的内存布局是相同的——您可以使用 CRect 作为任何需要 RECT 的函数的参数，反之亦然。
