c ++调用非默认构造函数作为成员 [英] c++ calling non-default constructor as member

问题描述

假设我有一个类A和一个类B. B用作A中的成员。B没有默认构造函数，但是需要一个参数。

let's say i have a class A and a class B. B is used as a member in A. B does not have a default constructor but one that requires a parameter.

class B {
  B(int i) {}
};


class A {

 B m_B;

 A()
 {
    m_B(17); //this gives an error
 }

};

我如何仍然在B中使用B作为会员？

how can i still use B as a member in A?

推荐答案

使用初始化列表。

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

class A {
    B m_B;
  public:
    A() : m_B(17) {}
};

BTW，以重置 m_B 构造函数，正确的语法是：

BTW, to reset m_B somewhere outside of the constructor, the correct syntax is:

m_B = B(17);

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