c ++类声明中静态对象的初始化
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c++ initialization of static object in class declaration
提问by bryan sammon
I have a C++ class (class1) with a static object of another class (class2) as a private member.
我有一个 C++ 类（class1），另一个类（class2）的静态对象作为私有成员。
I know upon using the program I will have to initialize the static object, I can use a default constructor for this (undesired value).
我知道在使用程序时我必须初始化静态对象，我可以为此使用默认构造函数（不需要的值）。
Is it possible to initialize the static object to my desired value only once, and only if I create an object of the containing class (class1)?
是否可以仅将静态对象初始化为我想要的值一次，并且仅当我创建包含类（class1）的对象时？
Any help would be appreciated.
任何帮助，将不胜感激。
回答by Seth Carnegie
Yes.
是的。
// interface
class A {
static B b;
};
// implementation
B A::b(arguments, to, constructor); // or B A::b = something;
However, it will be initialised even if you don't create an instance of the Aclass. You can't do it any other way unless you use a pointer and initialise it once in the constructor, but that's probably a bad design.
但是，即使您不创建A类的实例，它也会被初始化。除非您使用指针并在构造函数中将其初始化一次，否则您不能以任何其他方式执行此操作，但这可能是一个糟糕的设计。
IF you really want tothough, here's how:
如果你真的想要，这里是如何：
// interface
class A {
A() {
if (!Bptr)
Bptr = new B(arguments, to, constructor);
// ... normal code
}
B* Bptr;
};
// implementation
B* A::Bptr = nullptr;
However, like I said, that's most likely a bad design, and it has multithreading issues.
但是，就像我说的，这很可能是一个糟糕的设计，并且存在多线程问题。
