您如何为成员使用非默认构造函数?

问题描述

我有两个班

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;
}

我怎样才能让 aInstance 用 a(int i) 实例化，而不是尝试搜索默认构造函数?基本上，我想从 b 的构造函数中控制 a 的构造函数的调用.

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

你需要在构造函数初始化列表中显式调用a(int):

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.虽然它可以是任何整数.有关订单的重要说明和其他注意事项，请参阅评论.

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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