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From: Dave on 14 Feb 2010 02:26
Hi folks,

Got the following class hierarchy, and am getting a strange compile
error from it:

class RootFinder
{
public:
virtual ~RootFinder(){}

double findRoot( const Function1D& func, double guess ) const;
virtual double findRoot( const Function1D& func, double min, double
max ) const = 0;

private:
bool findGoodInterval( const Function1D& func, double guess, double&
min, double& max ) const;
};

class BisectionRootFinder : public RootFinder
{
public:
BisectionRootFinder(){}
virtual double findRoot( const Function1D& func, double min, double
max ) const;
};



If I then try to use the second class like so:

BisectionRootFinder rootFinder;
const double root = rootFinder.findRoot( func, guess );

I get the following compile error on that second line :

error C2660: 'BisectionRootFinder::findRoot' : function does not
take 2 arguments

I'm not sure why this is happening, as it should be able to find the
non-virtual version of findRoot(...) that is in the base class. I can
coax it to find it by doing the following:

BisectionRootFinder bisectRootFinder;
RootFinder& rootFinder = bisectRootFinder;
const double root = rootFinder.findRoot( func, guess );

and all works fine. But, why do I need to go through that extra step?
Am I declaring something wrong, or is VC just misbehaving? If it
matters, I am using Visual Studio 2008 Express (version 9.0.30729.1
SP)

Thanks.








From: David Lowndes on 14 Feb 2010 05:38
>I get the following compile error on that second line :
>
> error C2660: 'BisectionRootFinder::findRoot' : function does not
>take 2 arguments
>
>I'm not sure why this is happening, as it should be able to find the
>non-virtual version of findRoot(...) that is in the base class. I can
>coax it to find it by doing the following:
>
> BisectionRootFinder bisectRootFinder;
> RootFinder& rootFinder = bisectRootFinder;
> const double root = rootFinder.findRoot( func, guess );
>
>and all works fine. But, why do I need to go through that extra step?

The Comeau online compiler behaves exactly the same - so I'd hazard a
guess that it's what the standard says should happen.

Dave
From: David Wilkinson on 14 Feb 2010 06:09
Dave wrote:
> Hi folks,
>
> Got the following class hierarchy, and am getting a strange compile
> error from it:
>
> class RootFinder
> {
> public:
> virtual ~RootFinder(){}
>
> double findRoot( const Function1D& func, double guess ) const;
> virtual double findRoot( const Function1D& func, double min, double
> max ) const = 0;
>
> private:
> bool findGoodInterval( const Function1D& func, double guess, double&
> min, double& max ) const;
> };
>
> class BisectionRootFinder : public RootFinder
> {
> public:
> BisectionRootFinder(){}
> virtual double findRoot( const Function1D& func, double min, double
> max ) const;
> };
>
>
>
> If I then try to use the second class like so:
>
> BisectionRootFinder rootFinder;
> const double root = rootFinder.findRoot( func, guess );
>
> I get the following compile error on that second line :
>
> error C2660: 'BisectionRootFinder::findRoot' : function does not
> take 2 arguments
>
> I'm not sure why this is happening, as it should be able to find the
> non-virtual version of findRoot(...) that is in the base class. I can
> coax it to find it by doing the following:
>
> BisectionRootFinder bisectRootFinder;
> RootFinder& rootFinder = bisectRootFinder;
> const double root = rootFinder.findRoot( func, guess );
>
> and all works fine. But, why do I need to go through that extra step?
> Am I declaring something wrong, or is VC just misbehaving? If it
> matters, I am using Visual Studio 2008 Express (version 9.0.30729.1
> SP)

Them's the rules. Whne the compiler finds a matching name in
BisectionRootFinder, it will not look in the base class for a function with the
correct dignature. I used to think this was odd, but you get used to it.

It will work if you do

class BisectionRootFinder : public RootFinder
{
public:
using RootFinder::findRoot;
BisectionRootFinder(){}
virtual double findRoot( const Function1D& func, double min, double max ) const;
};

However, IMHO, this is not good style. There is really no reason to use the same
name for the two functions here.

--
David Wilkinson
Visual C++ MVP
From: Igor Tandetnik on 14 Feb 2010 08:19
Dave wrote:
> Got the following class hierarchy, and am getting a strange compile
> error from it:
>
> class RootFinder
> {
> public:
> virtual ~RootFinder(){}
>
> double findRoot( const Function1D& func, double guess ) const;
> virtual double findRoot( const Function1D& func, double min, double
> max ) const = 0;
>
> private:
> bool findGoodInterval( const Function1D& func, double guess, double&
> min, double& max ) const;
> };
>
> class BisectionRootFinder : public RootFinder
> {
> public:
> BisectionRootFinder(){}
> virtual double findRoot( const Function1D& func, double min, double
> max ) const;
> };

David Wilkinson explained why this doesn't work (a method in a derived class hides all methods with the same name in the base class). This is how I'd deal with it:

class RootFinder
{
public:
virtual ~RootFinder(){}

double findRoot( const Function1D& func, double guess ) const;
double findRoot( const Function1D& func, double min,
double max ) const;

private:
virtual double doFindRoot( const Function1D& func, double min, double
max ) const = 0;
};

class BisectionRootFinder : public RootFinder
{
public:
BisectionRootFinder(){}
private:
virtual double doFindRoot( const Function1D& func, double min, double
max ) const;
};

The two flavors of findRoot are public fronts to doFindRoot, which does the real work. See also

http://www.gotw.ca/publications/mill18.htm

--
With best wishes,
Igor Tandetnik

With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925
From: Alexander Grigoriev on 14 Feb 2010 12:11
THis is "name hiding" because of overload lookup rules.

You can deal with that by adding:

using RootFinder::findRoot;

in the derived class declaration.

"Dave" <thedaverudolf(a)gmail.com> wrote in message
news:19dfed9f-182c-4cc3-9bde-4a29905ce9e0(a)b36g2000pri.googlegroups.com...
> Hi folks,
>
> Got the following class hierarchy, and am getting a strange compile
> error from it:
>
> class RootFinder
> {
> public:
> virtual ~RootFinder(){}
>
> double findRoot( const Function1D& func, double guess ) const;
> virtual double findRoot( const Function1D& func, double min, double
> max ) const = 0;
>
> private:
> bool findGoodInterval( const Function1D& func, double guess, double&
> min, double& max ) const;
> };
>
> class BisectionRootFinder : public RootFinder
> {
> public:
> BisectionRootFinder(){}
> virtual double findRoot( const Function1D& func, double min, double
> max ) const;
> };
>
>
>
> If I then try to use the second class like so:
>
> BisectionRootFinder rootFinder;
> const double root = rootFinder.findRoot( func, guess );
>
> I get the following compile error on that second line :
>
> error C2660: 'BisectionRootFinder::findRoot' : function does not
> take 2 arguments
>
> I'm not sure why this is happening, as it should be able to find the
> non-virtual version of findRoot(...) that is in the base class. I can
> coax it to find it by doing the following:
>
> BisectionRootFinder bisectRootFinder;
> RootFinder& rootFinder = bisectRootFinder;
> const double root = rootFinder.findRoot( func, guess );
>
> and all works fine. But, why do I need to go through that extra step?
> Am I declaring something wrong, or is VC just misbehaving? If it
> matters, I am using Visual Studio 2008 Express (version 9.0.30729.1
> SP)
>
> Thanks.
>
>
>
>
>
>
>
>


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