C++ 构造函数初始化列表求值顺序
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Constructor initialization-list evaluation order
提问by Matt
I have a constructor that takes some arguments. I had assumed that they were constructed in the order listed, but in one case it appears they were being constructed in reverse resulting in an abort. When I reversed the arguments the program stopped aborting. This is an example of the syntax I'm using. The thing is, a_ needs to be initialized before b_ in this case. Can you guarantee the order of construction?
我有一个带有一些参数的构造函数。我曾假设它们是按照列出的顺序构建的，但在一种情况下，它们似乎是反向构建的，导致中止。当我反转参数时，程序停止中止。这是我正在使用的语法示例。问题是，在这种情况下， a_ 需要在 b_ 之前初始化。你能保证施工顺序吗？
e.g.
例如
class A
{
public:
A(OtherClass o, string x, int y) :
a_(o), b_(a_, x, y) { }
OtherClass a_;
AnotherClass b_;
};
回答by AraK
It depends on the order of member variable declaration in the class. So a_will be the first one, then b_will be the second one in your example.
这取决于类中成员变量声明的顺序。所以a_将是第一个，然后b_将是您的示例中的第二个。
回答by GManNickG
To quote the standard, for clarification:
引用标准，澄清一下：
12.6.2.5
Initialization shall proceed in the following order:
...
- 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).
...
12.6.2.5
初始化应按以下顺序进行：
...
- 然后，非静态数据成员应按照它们在类定义中声明的顺序进行初始化（同样与 mem 初始化程序的顺序无关）。
...
回答by Adam Getchell
The standard referencefor this now appears to be 12.6.2 section 13.3:
对此的标准参考现在似乎是 12.6.2 第 13.3 节：
(13.3) — 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).
(13.3) — 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（同样与 mem 初始化程序的顺序无关）。
