c ++继承，构造函数真正的调用者

Question

I have class A:

class A
{
    A(const String& name)
    {
        doSomething1();
    }
}

and I have also class B

class B : A
{
    B(const String& name): A(name)
    {
        doSomething2();
    }
}

So if I call B() it will call also A() and it will result with 2x calls doSomething(). Is there any way how to discover in A`s constructor that it is called directly like: A() and when indirectly: B() ?

Thanks

EDIT: Well ok, it is not the same method doSomething() it is more like doSomething1() and doSomething2() but I want call the most outside function so if A has doSomething1() and B doSomething2(), after call B() I want to execute just doSomething2()

Answer 1

In general there's no way to discover from a base class if the object you're referring to is of a derived type.

Anyway your design is most likely flawed, something like this could also work:

#include <iostream>
#include <string>
using namespace std;

class A
{
public:
    A(const string& name)
    {
        doSomethingFromA();
    }

    void doSomethingFromA() {
        cout << "called from A" << endl;
    };
protected:
   A(const string& name, bool fromB)
   {
       doSomethingFromB();
   }

   void doSomethingFromB() {
        cout << "called from B" << endl;
    };
};

class B : public A
{
    public:
    B(const string& name): A(name, true)
    {
    }

};


int main() {

    A obj1("str");

    B obj2("str");

    return 0;
}

http://ideone.com/jj8Df1

by exploiting the visibility of constructors you might pass additional info to the base class. Otherwise I'd advice using a slightly modified CRTP that renders your base class aware of the object itself (they become an entire different entity).

Answer 2

You could have two overloads of doSomething as follow but...

void doSomething(A*);
void doSomething(B*);

And on the call site you do:

doSomething(this);

( this is either A* or B* so it will call the appropriate function.)

class A
{
    A(const String& name)
    {
        doSomething(this);
    }
}

class B : A
{
    B(const String& name): A(name)
    {
        doSomething(this);
    }
}

But , as other said in the comment, you have a design issue!