构造器指定所有内置成员的零初始化？ [英] Constructor to specify zero-initialization of all builtin members?

问题描述

对于类的构造函数，有没有更简单的方法来指定内置类型的所有成员应该被初始化为零？

Is there a simpler way for a class's constructor to specify that all members of built-in type should be zero-initialized?

此代码段在另一篇文章中出现：

This code snippet came up in another post:

struct Money
{
    double amountP, amountG, totalChange;
    int twenty, ten, five, one, change;
    int quarter, dime, nickel, penny;

    void foo();
    Money()  {}
};

结果证明问题是对象通过

and it turned out that the problem was that the object was instantiated via Money mc; and the variables were uninitialized.

建议的解决方案是添加以下构造函数：

The recommended solution was to add the following constructor:

Money::Money()
  : amountP(), amountG(), totalChange(),
    twenty(), ten(), five(), one(), change()
    quarter(), dime(), nickel(), penny()
{
}

但是，这是丑陋，不便于维护。很容易添加另一个成员变量，忘记将其添加到构造函数中的长列表中，可能导致在未初始化的变量突然停止获取 0 。

However, this is ugly and not maintenance-friendly. It would be easy to add another member variable and forget to add it to the long list in the constructor, perhaps causing a hard-to-find bug months down the track when the uninitialized variable suddenly stops getting 0 by chance.

推荐答案

您可以使用子对象初始化。成员工作，但是你需要限定所有访问。所以继承更好：

You can use a subobject to initialize en masse. A member works, but then you need to qualify all access. So inheritance is better:

struct MoneyData
{
    double amountP, amountG, totalChange;
    int twenty, ten, five, one, change;
    int quarter, dime, nickel, penny;
};

struct Money : MoneyData
{
    void foo();
    Money() : MoneyData() {} /* value initialize the base subobject */
};

演示（刊登位置 new 请确保在创建对象之前内存不为0）： http://ideone.com/P1nxN6

Demonstration (placement new is used to make sure the memory is non-zero before object creation): http://ideone.com/P1nxN6

与问题中的代码略有不同： http：// ideone。 com / n4lOdj

Contrast with a slight variation on the code in the question: http://ideone.com/n4lOdj

在上述两个演示中， double 成员都被删除， / NaN编码。

In both of the above demos, double members are removed to avoid possible invalid/NaN encodings.

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