在初始化变量之前是否调用父类构造函数？ [英] Are parent class constructors called before initializing variables?

问题描述

在初始化变量之前调用父类构造函数，还是编译器首先初始化该类的变量？

Are parent class constructors called before initializing variables, or will the compiler initialize the variables of the class first?

例如：

class parent {
protected:
  int a;
public:
  parent() : a(123) {};
};

class child : public parent {
  int b;
public:
            // question: is parent constructor done before init b?
  child() : b(456), parent() {};
}

推荐答案

在非委托构造函数中，初始化在
中按如下顺序进行：

In a non-delegating constructor, initialization proceeds in the following order:

首先，只有最多
派生类（1.8）的构造函数，虚拟基类按照
的顺序初始化，它们出现在定向$ b的深度优先从左到右的遍历中$ b基类的非循环图，其中从左到右是在导出类
base-specifier-list中基类的外观的
的顺序。

— First, and only for the constructor of the most derived class (1.8), virtual base classes are initialized in the order they appear on a depth-first left-to-right traversal of the directed acyclic graph of base classes, where "left-to-right" is the order of appearance of the base classes in the derived class base-specifier-list.

- 然后，直接基类在
声明顺序中初始化，因为它们出现在base-specifier-list
存储器初始化器）。

— Then, direct base classes are initialized in declaration order as they appear in the base-specifier-list (regardless of the order of the mem-initializers).

- 然后，非静态
数据成员按照它们在
类定义中声明的顺序进行初始化（同样不考虑
mem-initializers）。

— Then, non-static data members are initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).

- 最后，执行
构造函数体的复合语句。

— Finally, the compound-statement of the constructor body is executed.

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