C++ 类/结构成员的默认可见性
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default visibility of C++ class/struct members
提问by S I
In C++, why is private the default visibility for members of classes, but public for structs?
在 C++ 中，为什么类成员的默认可见性是私有的，而结构是公共的？
回答by Oren Trutner
C++ was introduced as a superset of C. Structs were carried over from C, where the semantics of their members was that of public. A whole lot of C code exists, including libraries that were desired to work with C++ as well, that use structs. Classes were introduced in C++, and to conform with the OO philosophy of encapsulation, their members are private by default.
C++ 是作为 C 的超集引入的。结构是从 C 继承而来的，其成员的语义是公共的。存在大量 C 代码，包括希望与 C++ 一起使用的库，它们使用结构。类是在 C++ 中引入的，为了符合 OO 的封装哲学，它们的成员默认是私有的。
回答by a_m0d
Because a class is a usual way of doing object orientation, which means that member variables should be private and have public accessors - this is good for creating low coupling. Structs, on the other hand, have to be compatible with C structs, which are always public (there is no notion of public and private in C), and don't use accessors/mutators.
因为类是面向对象的常用方式，这意味着成员变量应该是私有的并具有公共访问器 - 这有利于创建低耦合。另一方面，结构必须与 C 结构兼容，C 结构始终是公共的（C 中没有公共和私有的概念），并且不使用访问器/修改器。
回答by Karl Voigtland
Probably for backwards compatibility with C structs. This way structs declared in C code will continue to work the same way when used in C++ code.
可能是为了与 C 结构向后兼容。这样，在 C 代码中声明的结构体在 C++ 代码中使用时将继续以相同的方式工作。
