没有适当的默认构造函数可用错误

Question

这是我的代码：

class package
{
protected:
    string name;
    string city;
    string state;
    int zip;
    double weight;
    double costPerOunce;

public:

    package::package(string Name, string City, string State, int Zip, double Weight, double CostPerOunce):
      name(Name), city(City), state(State),
      zip(Zip), weight(Weight), costPerOunce(CostPerOunce)
      {

      }
      double calculateCost()
    {
        return (weight * costPerOunce);
    }

};
class twoDayPackage: public package
{
protected:
    double flatFee;
public:
    twoDayPackage::twoDayPackage(double FlatFee):
      flatFee(FlatFee)
      {

      }
    double calculateCost()
    {
        return (weight * costPerOunce) + flatFee;

    }
};
int main()
{


    system ("pause");
    return 0;
}

我尝试运行这段代码，我得到的错误如下： error C2512: 'package' : 没有合适的默认构造函数可用

该错误与基类构造函数的继承有关，但我不知道代码未运行的确切原因。请帮帮我。

Answer 1

twoDayPackage::twoDayPackage(double FlatFee):
  flatFee(FlatFee)

正在调用基本构造函数package()，因为您没有指定任何其他内容。

在类包中添加一行package::package(){}; :)

Answer 2

你需要一个包的构造函数。 另外，在声明构造函数时不需要package::package(...)（这是在cpp文件中定义它时）。只需package(...)就可以了。

class package
{
protected:
    string name;
    string city;
    string state;
    int zip;
    double weight;
    double costPerOunce;

public:
    package()
    {}
    // \/ You don't need package:: that's only needed when you define the func in cpp
    package(
        string Name, string City, string State, int Zip, 
        double Weight, double CostPerOunce
    )
        : name(Name), city(City), state(State),
        zip(Zip), weight(Weight), costPerOunce(CostPerOunce)
    {

    }
    double calculateCost()
    {
        return (weight * costPerOunce);
    }

};

Answer 3

twoDayPackage 的构造函数将首先创建package，然后再构造flatFee。由于您没有告诉它如何执行此操作，它会寻找构造 package 的默认方式。

当您构造twoDayPackage 时，您需要为它提供构造底层package 所需的一切。要么，要么让它确定要传递给package 构造函数的值。

传入所需的参数如下所示：

class twoDayPackage {
public:
    twoDayPackage(string Name, string City, string State, int Zip, double Weight, double CostPerOunce, double flatFee) :
    package(Name, City, State, Zip, Weight, CostPerOunce),
    flatFee(flatFee) {
    }
    //..
};