Re: Question about Name Hiding concept

From:

=?UTF-8?B?RXJpayBXaWtzdHLDtm0=?= <Erik-wikstrom@telia.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 18 Jan 2008 22:50:29 GMT

Message-ID:

<V2akj.2949$R_4.2278@newsb.telia.net>

On 2008-01-18 23:02, developer.new wrote:

Hi

I have a question regarding this concept I learned about recently:
Name Hiding. Here's what I've come across:
There is a base class with two functions with the same name but
different signature. A class inherits publicly from this base class
and redefines one of the two functions in the derived class. In that
case, a derived class object cannot access the other base class
function that it hasn't redefined. I'm posting a code snippet to make
it clear.

class Base {
public:
  int f () { cout << "Base::f_int" << endl; return 1; }
  int f (string s_) { cout << "Base::f_str" << endl; return 1; }
};

class Derived : public Base {
public:
  int f() { cout << "Derived::f_int" << endl; return 1;}
};

int main() {
  string str_ = "blahhh";
  Derived d1;
  d1.f();
  d1.f(str_); //Gives compilation error!!!!!!
  d1.Base::f(str_); //This of course, works.

  return 0;
}

Going by how C++ uses name mangling to create unique function names, I
thought it would be possible to access the Base class "int f (string)"
function directly from the derived object.

Any idea why this cannot be done? I know it's a not a good practice to
have functions with duplicate names and all that. But my question is
more about inheritance. Why does this function become inaccessible
from the derived class?

It is because of the way names are looked up. IIRC it goes something
like this, first the current context is searched for any function with
the right name, if you find one or more goto next step, if not search in
a "outer" context (such as base-classes, global namespaces etc.). Next
the list of functions found are examined to see if any of them matches
the function arguments (and if none is found you try with conversions).

Since a name is found in the derived class the base-class is never
searched and thus the matching function will not be found. Why things
are done is this way you will have to ask in comp.std.c++.

--
Erik Wikstr?m