Compiler Error for classes in hierarchy

Question

I have the following code

class interfaceBase // abstract class
{
public:
    virtual void vf1() = 0;
};

class tempBase : public interfaceBase  // manages a resource
{
    tempBase(int a) { var = new int[a]; }
    ~tempBase(){ free(var); }
private:
    int* var;
};

class derived : public tempBase // class I intend to instantiate.
{
public:
    derived(int rhs){ tempBase(var); } // ERROR - Pasted below
    void vf1() override final {}
};

int main()
{
    int a = 5;
    derived d(a);
}

I have a resource that needs to be managed, I created a seperate class called tempBase whose job is to manage that resource. However, this leaves me with a problem - I cannot construct objects of type derived , because there seems no means to call the constructor to tempBase

I get the error saying

error C2512: 'tempBase' : no appropriate default constructor available
error C2259: 'tempBase' : cannot instantiate abstract class

How can I change my code such that I might still have all the resource management handled by tempBase , and have derived instantiable also.

Answer 1

You ave to put this in the initializer list:

derived(int rhs) : tempBase(var) { } // No erroranymore - see below

Some additional explanation about the errors in your original code:

• As there was no initializer for tempBase , the compiler tried to generate a default constructor, so that all member variables are constructed before executing the constructor body.
• You tempBase(var) in the body would create an additional temporary anonymous object of class tempBase , but such direct instantiation of a pure virtual class is not allowed

Answer 2

在构造派生对象的基础部分时，您需要使用

derived(vars) : base(vars) { constructor code here }