can I dynamically convert a base class object into a derived class object?
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e.g:
class DerivedClass:BaseClass
{
void functionInDerivedClassOnly();
}
BaseClass pBaseClass = new BaseClass();
//can the following line be excuted correctly?
(DerivedClass*)pBaseClass->functionInDerivedClassOnly();
delete pBaseClass;Thank you very much!!! ------------------- I am learning C++ and English
This will help you: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccelng/htm/express_72.asp[^]
Jesus Loves:rose:
--Owner Drawn:rose: --Nothing special --Defeat is temporary but surrender is permanent --Never say quits --Jesus is Lord:rose:
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In general no. In the code above the compiler will go ahead and treat
pBaseClassas aDerivedClassbut unless it really is one you're asking for trouble. SteveThank you guys, I finally understand it with your help. Only if it "is" actually the "specified type" in the memory can you convert it into the "specified type" . I have thought through and figure that maybe my problem dose be a complicated one and I can't find a short cut for it . Thank you very much, again!!! ------------------- I am learning C++ and English
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e.g:
class DerivedClass:BaseClass
{
void functionInDerivedClassOnly();
}
BaseClass pBaseClass = new BaseClass();
//can the following line be excuted correctly?
(DerivedClass*)pBaseClass->functionInDerivedClassOnly();
delete pBaseClass;Thank you very much!!! ------------------- I am learning C++ and English
ewighell wrote:
BaseClass pBaseClass = new BaseClass();
replace with
BaseClass pBaseClass = new DerivedClass();
that's what polymorphism was designed for !
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...] -- modified at 3:46 Thursday 19th January, 2006 -
In general no. In the code above the compiler will go ahead and treat
pBaseClassas aDerivedClassbut unless it really is one you're asking for trouble. SteveScore: 1.8 (2 votes).
How are the scores calculated? Obviously not an average as 3.6 (2x1.8) can't be obtained by adding 2 scores. Steve
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your answer is similar with my guess. but is there any way to implement the dynamical conversion from the base class object to a derived one. if not ,I would have to delete the base class object and recreate a derived one with the
newoperator. in this case I can't see the benefit of the inheritance, can I? Thank you very much!!! ------------------- I am learning C++ and EnglishMaybe we can help you if you describe clearly what you need to do
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e.g:
class DerivedClass:BaseClass
{
void functionInDerivedClassOnly();
}
BaseClass pBaseClass = new BaseClass();
//can the following line be excuted correctly?
(DerivedClass*)pBaseClass->functionInDerivedClassOnly();
delete pBaseClass;Thank you very much!!! ------------------- I am learning C++ and English
just by casting the baseclass pointer to derived class pointer does not make the object that was created i.e. baseclass into a dereived class. Its just like calling Donkey a dog does not make donkey to bark ;). so you can do this.
BaseClass* pBaseClass = new DerivedClass(); ((DerivedClass*)pBaseClass)->functionInDerivedClassOnly();or usereinterpret_cast
-Prakash
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just by casting the baseclass pointer to derived class pointer does not make the object that was created i.e. baseclass into a dereived class. Its just like calling Donkey a dog does not make donkey to bark ;). so you can do this.
BaseClass* pBaseClass = new DerivedClass(); ((DerivedClass*)pBaseClass)->functionInDerivedClassOnly();or usereinterpret_cast
-Prakash
hey, you posted the same thing as i did 1 hour later :sigh: where were you ? :|
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...] -
Score: 1.8 (2 votes).
How are the scores calculated? Obviously not an average as 3.6 (2x1.8) can't be obtained by adding 2 scores. Steve
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hey, you posted the same thing as i did 1 hour later :sigh: where were you ? :|
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...]He reinterpreted it.;P
Jesus Loves:rose:
--Owner Drawn:rose: --Nothing special --Defeat is temporary but surrender is permanent --Never say quits --Jesus is Lord:rose:
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He reinterpreted it.;P
Jesus Loves:rose:
--Owner Drawn:rose: --Nothing special --Defeat is temporary but surrender is permanent --Never say quits --Jesus is Lord:rose:
Owner drawn wrote:
He reinterpreted it
without quoting or refering to me ?! ;P not that sure...
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...] -
just by casting the baseclass pointer to derived class pointer does not make the object that was created i.e. baseclass into a dereived class. Its just like calling Donkey a dog does not make donkey to bark ;). so you can do this.
BaseClass* pBaseClass = new DerivedClass(); ((DerivedClass*)pBaseClass)->functionInDerivedClassOnly();or usereinterpret_cast
-Prakash
In the example above you should use
static_cast<DerivedClass*>(pBaseClass). It's safer (but still not 100% safe) as it will only compile if it's possible forBaseClasss to exist which are alsoDerivedClasss (there is an inheritance relationship between them). Steve -
hey, you posted the same thing as i did 1 hour later :sigh: where were you ? :|
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...]toxcct wrote:
hey, you posted the same thing as i did 1 hour later
I did not read the other solutions ;)
-Prakash
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In the example above you should use
static_cast<DerivedClass*>(pBaseClass). It's safer (but still not 100% safe) as it will only compile if it's possible forBaseClasss to exist which are alsoDerivedClasss (there is an inheritance relationship between them). SteveStephen Hewitt wrote:
In the example above you should use static_cast(pBaseClass)
yes, correct. Thanks.
-Prakash
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hey, you posted the same thing as i did 1 hour later :sigh: where were you ? :|
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...] -
Score: 1.8 (2 votes).
How are the scores calculated? Obviously not an average as 3.6 (2x1.8) can't be obtained by adding 2 scores. Steve
the scores are ponderated with the level of the members... - a bronze member votes for 1 voice - a silver member votes for 2 voices - a gold member votes for 4 voices - a platinum member votes for 8 voices
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...] -
toxcct wrote:
where were you ?
Me, Sleeping :)
"Opinions are neither right nor wrong. I cannot change your opinion. I can, however, change what influences your opinion." - David Crow
cheers, Alok Gupta VC Forum Q&A :- I/ IV
:zzz::zzz: zzzZZZZZZZzzzzz SShhhhhhh :zzz::zzz:
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...] -
the scores are ponderated with the level of the members... - a bronze member votes for 1 voice - a silver member votes for 2 voices - a gold member votes for 4 voices - a platinum member votes for 8 voices
TOXCCT >>> GEII power
[toxcct][VisualCalc 2.20][VCalc 3.0 soon...]Ahhh Steve