Question

I want to call a method from A class in constructor of other class

I googled, but did not find any answer
For example, I have :

class A{
  void doWork();
}
class B{
  B(){
   //here i want to have doWork method
 }
}

Answer 1

You told us not enough to choose proper solution. Everything depends on what you are trying to achieve. A few solutions:

a) Mark A method as static.

class A
{
public:
    static void DoSth()
    {
        // Cannot access non-static A members here!
    }
};

class B
{
public:
    B()
    {
        A::DoSth();
    }
};

b) You can instantiate A in place

class A
{
public:
    void DoSth()
    {
        // Do something
    }
};

class B
{
public:
    B()
    {
        A a;
        a.DoSth();
    }
};

c) You can put A’s instance into B:

// A remains as in b)

class B
{
private:
    A a;
    // or: A * a;

public:
    B()
    {
        a.DoSth();
        // or: a = new A; a->DoSth();
        // Remember to free a somewhere
        // (probably in destructor)
    }
}

d) You may derive B from A:

class A
{
protected:
    void DoSth()
    {
    }
};

class B : public A
{
public:
    B()
    {
        DoSth();
    }
};

e) You can forget about A class and make DoSth a function:

void DoSth()
{
    // ...
}

class B
{
public:
    B()
    {
        DoSth();
    }
}

Since you provided not enough data, you have to choose solution on your own.