[Qt-interest] Problem with Base Class Method in Derived Class

[Marco Borm]

Hi Phil,

since 12 years of development in C++ I always thought this was a bug, 
but never searched about that.
Unfortunatly the VC compiler never gave me a hint like the GCCs 
"‘virtual void x::some_method(QString)’ was hidden".
So thank you very much for the explanation.

Marco

phil prentice wrote:
> Hi
>   I dont know if I am misunderstanding the problem.
>   However I am not a C++ expert and am working hard to understand QT.
>   I have read the following statement in the online version of 
> "An Introduction to design patterens in C++ with QT"
>
>  A member function of a derived class with the same name as a function in the 
> base class hides all functions in the base class with that name. In such a 
> case.
>     * Only the derived class function can be called directly.
>     *The class scope resolution operator may be used to call hidden base 
> functions explicitly. 
>
> Please see
>   
> http://cartan.cas.suffolk.edu/oopdocbook/opensource/overloadhide.html
>
> I hope I have'nt misunderstood anything.
>
> Phil
> On Thursday 07 May 2009 06:25, Marco Borm wrote:
>   
>> Hi Shimaron,
>>
>> I think your code is complete ok.
>> I had the same problem many times and think and the reason for that was
>> the buggy MS compiler I used, not that this code was invalid. The GCC
>> just worked in that cases as I expected.
>> What compiler are you using?
>>
>>
>> Greetings,
>> Marco
>>
>> Shimaron Greywolf wrote:
>>     
>>> Here's one strange problem - probably not really a Qt one, but
>>> probably someone can help.
>>>
>>> I thought I had my share of C++ design and coding, but the following
>>> was new to me. Consider this code:
>>>
>>> ===== test.h
>>>
>>> #include <QString>
>>> class x
>>> {
>>> public:
>>>      virtual ~x();
>>>      virtual void some_method(const QString i);
>>> };
>>>
>>> class xx : public x
>>> {
>>> public:
>>>      virtual void some_method(const int i);
>>>      virtual ~xx();
>>> };
>>>
>>> ====== test.cpp
>>>
>>> #include <QDebug>
>>> #include "test.h"
>>> int main()
>>> {
>>>      xx * yy = new xx();
>>>      yy -> some_method((int)65);
>>>      yy -> some_method(QString("foo"));
>>> }
>>>
>>>
>>>
>>> x::~x() {}
>>> void x::some_method(const QString i) {qDebug()<<"x::QString";}
>>> void xx::some_method(const int i) {qDebug()<<"xx::int";}
>>> xx::~xx() {}
>>>
>>>
>>> =========
>>>
>>> My expectation was that in the new xx object, I'd have access to the
>>> base class method some_method(const QString) - which I don't, as the
>>> compiler tells me:
>>>
>>> src# make
>>> compiling test.cpp
>>> test.cpp: In function ‘int main()’:
>>> test.cpp:7: error: no matching function for call to
>>> ‘xx::some_method(QString)’
>>> test.h:12: note: candidates are: virtual void xx::some_method(int)
>>> test.cpp: At global scope:
>>> test.cpp:13: warning: unused parameter ‘i’
>>> test.cpp:14: warning: unused parameter ‘i’
>>> make: *** [test.o] Error 1
>>>
>>> If I store the xx object in an x pointer (i.e. baseclass pointer), it
>>> works, but I lose access to any additional functionality of my derived
>>> class xx.
>>>
>>> Why isn't some_method(const QString) resolved properly?
>>>
>>> Thanks for your help!
>>>
>>> Shimaron
>>>
>>>
>>> _______________________________________________
>>> Qt-interest mailing list
>>> Qt-interest at trolltech.com
>>> http://lists.trolltech.com/mailman/listinfo/qt-interest
>>>       
>> _______________________________________________
>> Qt-interest mailing list
>> Qt-interest at trolltech.com
>> http://lists.trolltech.com/mailman/listinfo/qt-interest
>>     
>
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at trolltech.com
> http://lists.trolltech.com/mailman/listinfo/qt-interest
>
>