重载父 class 构造函数。错误的初始化器选择？

Question

我想添加一个 Child class 到一个已经定义和声明了 Parent 的现有项目。 Parent class 有两个带有初始化列表的构造函数。这是我的代码，它会生成错误 C2668：'Parent::Parent'：对重载函数的调用不明确。我的错误在哪里？

感谢@Mape

#include <stdio.h>

class Parent
{
public:
// Here a constructor with one default trailing argument, i.e. myInt,
// myDouble is not initialised. This is correct, as once one argument
// is initialised, the rule is that all the following ones have to be 
// initialised, but the previous ones may not be. 
Parent(double myDouble, int myInt=5);
// Here a defauls contructor, as all its arguments (one indeed) are 
// initialised
Parent(double myDouble=0);
double m_dVar;
int m_iVar;
};

class Child : public Parent
{
public:
// derived class has to redefine the constructors. 
// Q1: All of them?
// Q2: With the same default arguments?
Child(double myDouble, int myInt=0);
Child(double myDouble=0);
}; 

class User
{
public:
User();
Parent* m_pGuy;
Child* m_pSonOfGuy;
};

// Base Class Implementation
Parent::Parent(double myDouble, int myInt)
{
    m_dVar=myDouble;
    m_iVar=myInt;
}

Parent::Parent(double myDouble)
{
    m_dVar=myDouble;
    m_iVar=3;
}

// Derived Class Implementation
// the two arguments contructor is easily implemented. 
Child::Child(double myDouble, int myInt)
   :   Parent(myDouble*2, myInt+1)
{
}
// the one argument contructor may trigger ERROR: 
// "ambiguous call to overloaded function."
// (C2668 in Microsoft Visual Studio compiler)
Child::Child(double myDouble)
    //:   Parent(0) ERROR
    :   Parent() //OK
{
    m_iVar=9;
}

User::User()
    :    m_pGuy(0) 
{  
}

// main{
int main(void)
{
   User user1();
   //Parent parent;
   Child child1(8.3,1);
   printf("\n\nChild  m_dVar %f",child1.m_dVar);
   printf("\nChild  m_iVar %d",child1.m_iVar);
   return 0;
}

Answer 1

编译器不知道您打算调用哪个构造函数。例如，您的 Parentclass 构造函数在使用一个参数调用时实际上具有相同的函数签名。

Parent::Parent(double myDouble, int myInt=0) {
    cout << "Foo";
}
Parent::Parent(double myDouble) {
    cout << "Bar";
}

// later
Parent *parent = new Parent(1.2345);  // Compiler: which constructor to call?
                                      // does this mean Parent(1.2345, 0)
                                      // or Parent(1.2345)

这是要打印 Foo 还是 Bar？

让它发挥作用

更改代码，使 myInt 参数不是可选的。

或

删除另一个只接受myDouble作为参数的构造函数。

重载父 class 构造函数。错误的初始化器选择？

Overloaded parent class constructors. Wrong inizializer choice?

constructor

parent-child

default-constructor

initializer-list

default-arguments