c++ - 类中成员声明顺序如果相互依赖，最优解

Question

如果我有一个包含更多成员的类，并且其中一些成员依赖于其他成员，那么声明其成员的最佳方式是什么？例如:

class MyClass
{
private:
  MyOb1 Obj1;
  MyOb2 Obj2;
  int i;
  std::string str;

public:
  MyClass(int iIn, const std::string& strIn)
  : i(iIn),      // here
    str(strIn),
    Obj1(i),
    Obj2(i, str) {}
}

由于申报顺序的原因，出现了一些问题。我选择了那个顺序，因为它是一个最优顺序。我在 MyClass 的其他函数中需要这些值。这个问题的最佳解决方案是什么？

Answer 1

由于初始化顺序取决于它们在您的类中定义的顺序，因此忽略成员顺序:C++: Initialization Order of Class Data Members .

所以我只是将整数和字符串移到 MyOb1 和 MyOb2 上面，@Matt McNabb 也指出你应该使用在你的构造函数中传递的参数初始化 MyOb1/2 对象以避免歧义(明智的建议):

class MyClass
{
private:
  int i;
  std::string str;
  MyOb1 Obj1;
  MyOb2 Obj2;


public:
  MyClass(int iIn, const std::string& strIn)
  : i(iIn),      // here
    str(strIn),
    Obj1(iIn),
    Obj2(iIn, strIn) {}
}

引用标准第 12.6.2 节(最新的 draft 在第 266 页有这个):

5 Initialization shall proceed in the following order:

— First, and only for the constructor of the most derived class as described below, virtual base classes shall be 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 class names in the derived class base-specifier-list.

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

— Then, nonstatic data members shall be initialized in the order they were declared in the class definition (again regardless of the order of the mem-initializers).

— Finally, the body of the constructor is executed. [Note: the declaration order is mandated to ensure that base and member subobjects are destroyed in the reverse order of initialization. ]