How to pass method result as parameter to base class constructor in C++?

class Base
{
  public:

  Base(string S)
  {
  ...
  };
}

class Derived: Base
{
public:
  int foo;
  string bar()
  {
    return stringof(foo); // actually, something more complex
  };

  Derived(int f) : foo(f), Base(bar())
  {
  };
}

class Derived: Base
{
public:
  int foo;

  static string bar(int f)
  {
    return stringof(f); // actually, something more complex
  }

  string bar()
  {
    return bar(foo);
  };

  Derived(int f) :  Base(bar(f)) , foo(f)
  {
  };
}

Derived(int f) : Base(stringof(f)), foo(f) {}

class Base {
public:
    Base(string S) {  ...  }
    void bat() { ... }
};

class Derived {
    Base *base;
    int foo;

public:
    Derived(int f) : base(NULL), foo(f) {
        base = new Base(bar());
    }
    ~Derived() {
        delete base;
    }

    string bar() {
        return stringof(foo); // actually, something more complex
    }

    void bat() {
        base->bat();
    }
};

class Derived: Base
{
public:
  int foo;
  string bar()
  {
    return stringof(foo); // actually, something more complex
  };

  Derived(int f) : foo(f), Base(bar())
  {
  };
}

class Derived: Base
{
public:
  int foo;
  static string bar(int f)
  {
    return stringof(f); // actually, something more complex
  };

  Derived(int f) : Base(bar(f)), foo(f)
  {
  };
}