Solved

Why doesn't the compiler see overloaded base class functions?

Posted on 2002-05-15
7
191 Views
Last Modified: 2010-04-02
Why doesn't the compiler see overloaded base class functions? I cannot explain why the follwing is an error:

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

    class Base
    {
      public:
        virtual void Do( const string& )
        {
          cout << "Base::Do( string )" << endl;
        }
        virtual void Do( const char* const data,
                                  const long length )
        {
          cout << "Base::Do( char*, long )" << endl;
        }
    };

    class Derived : public Base
    {
      public:
        virtual void Do( const int s )
        {
          cout << "Base::Do( int )" << endl;
        }
    };

    int main(int argc, char* argv[])
    {
      Derived d;
      d.Do( 5 );
      d.Do( string() );
      d.Do( "foobar", 6 );
      return 0;
    }

Why doesn't the compiler "see" the base class versions of Do()? The only way I can get this to compile is to qualify the calls by adding "Base::", like so:

    d.Base::Do( string() );
    d.Base::Do( "foobar", 6 );

Can someone explain to me why this is the case? Thanks!
0
Comment
Question by:magenta
7 Comments
 

Author Comment

by:magenta
ID: 7012178
I should have pointed out that the compiler complains about the following lines:

     d.Do( string() );
     d.Do( "foobar", 6 );

It seems to only see the Derived methods.
0
 
LVL 6

Accepted Solution

by:
thienpnguyen earned 50 total points
ID: 7012402
In subclass, if you have a overload funtion that is same name with a fucntion in base class, then that function in base class will be hide .

0
 
LVL 6

Expert Comment

by:thienpnguyen
ID: 7012417
For fixing the bug, you can do as following

class Derived : public Base
{
public:

    using  Base::Do; // <-------- new code

    virtual void Do( const int s )
    {
      cout << "Base::Do( int )" << endl;
    }

};

int main(int argc, char* argv[])
{
  Derived d;
  d.Do( 5 );
  d.Do( string() );
  d.Do( "foobar", 6 );
  return 0;
}
0
Highfive Gives IT Their Time Back

Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

 
LVL 6

Expert Comment

by:thienpnguyen
ID: 7012427
0
 
LVL 3

Expert Comment

by:MDarling
ID: 7012450
This is not meant to trample on thienpnguyen's answer.

Just thought I'd post the full listing as I got it to compile on M$ VC6.0.

Nice links Thien! Almost perfect for this question.




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

class Base
{
public:
     virtual void Do( const string& )
     {
          cout << "Base::Do( string )" << endl;
     }
     virtual void Do( const char* const data,
          const long length )
     {
          cout << "Base::Do( char*, long )" << endl;
     }
};

class Derived : public Base
{
public:
     
     Base::Do;
     
     virtual void Do( const int s )
     {
          cout << "Base::Do( int )" << endl;
     }
};

int main(int argc, char* argv[])
{
     Derived d;
     d.Do( 5 );
     d.Do( string() );
     d.Do( "foobar", 6 );
     return 0;
}
0
 

Author Comment

by:magenta
ID: 7012541
Very intesting...I'm going to have to sit down and read that article. I should probably have the C++ standard nearby...

However, before I do that, answer this question. If a derived class by definition can be treated the same as a base class, then isn't the code above example of this rule being broken?
0
 
LVL 11

Expert Comment

by:griessh
ID: 7178762
Dear magenta

I think you forgot this question. I will ask Community Support to close it unless you finalize it within 7 days. You can always request to keep this question open. But remember, experts can only help you if you provide feedback to their questions.
Unless there is objection or further activity,  I will suggest to accept

     "thienpnguyen"

comment(s) as an answer.
     "refund the points and delete this question"
since nobody had a satisfying answer for you.
since you never gave more feedback.
PAQ at zero points.

If you think your question was not answered at all, you can post a request in Community support (please include this link) to refund your points. The link to the Community Support area is: http://www.experts-exchange.com/commspt/


PLEASE DO NOT ACCEPT THIS COMMENT AS AN ANSWER!
======
Werner
0

Featured Post

IT, Stop Being Called Into Every Meeting

Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

Join & Write a Comment

Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
What is C++ STL?: STL stands for Standard Template Library and is a part of standard C++ libraries. It contains many useful data structures (containers) and algorithms, which can spare you a lot of the time. Today we will look at the STL Vector. …
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.

705 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

20 Experts available now in Live!

Get 1:1 Help Now