如何为成员使用非默认构造函数？ [英] How do you use the non-default constructor for a member?

问题描述

我有两个类

class a {
    public:
        a(int i);
};

class b {
    public:
        b(); //Gives me an error here, because it tries to find constructor a::a()
        a aInstance;
}

如何获得它，使aInstance用一个而不是试图搜索默认构造函数？基本上，我想控制从b的构造函数中调用a的构造函数。

How can I get it so that aInstance is instantiated with a(int i) instead of trying to search for a default constructor? Basically, I want to control the calling of a's constructor from within b's constructor.

推荐答案

在构造函数初始化器列表中：

You need to call a(int) explicitly in the constructor initializer list:

b() : aInstance(3) {} 

其中3是您要使用的初始值。虽然它可以是任何int。查看有关订单和其他警告的重要注意事项的注释。

Where 3 is the initial value you'd like to use. Though it could be any int. See comments for important notes on order and other caveats.

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