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07-08-2009, 12:35 PM
| #1 |
| Registered User Join Date: Mar 2009
Posts: 35
| Why Virtual base class increase the size of class by 4 bytes? Well I have a quick doubt on virtual base class: can sombody explain? I am going to write 2 c++ program please check output. Code: #include<iostream>
using namespace std;
class base
{
int i;
};
class derived: public base
{
};
void main()
{
cout<<"size of class derived is "<<sizeof(derived)<<endl;
}
OUTPUT:
size of class derived is 4
Press any key to continue
With virtual:
#include<iostream>
using namespace std;
class base
{
int i;
};
class derived:virtual public base
{
};
void main()
{
cout<<"size of class derived is "<<sizeof(derived)<<endl;
}
OUTPUT:
size of class derived is 8
Press any key to continue
|
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|
07-08-2009, 12:51 PM
| #2 |
| Registered User Join Date: Jul 2009 Location: Puget Sound, WA
Posts: 3
| Well one don't use void main(), it's int and must return zero on success. What do you want to know about virtual classes or what is your doubt? |
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|
07-08-2009, 12:59 PM
| #3 | |
| Registered User Join Date: Mar 2009
Posts: 35
| Quote:
output of1st is 4 byte and output of second is 8 byte(uisng virtual base class). Now my doubt is, mentioned in title. i.e. "will Virtual base class increase the size of a class". Thanks for telling me about usage of int main instead of void main. | |
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|
07-08-2009, 01:22 PM
| #4 |
| Registered User Join Date: Jul 2009 Location: Puget Sound, WA
Posts: 3
| I just skim thread titles nowadays; since most of them on a good percentage of sites involve the words "please, give, me" in all caps. Is your compiler just treating based:derived in the first example as the same [empty] class? Last edited by MosaicFuneral; 07-08-2009 at 01:25 PM. |
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07-08-2009, 01:30 PM
| #5 |
| Algorithm Dissector  Join Date: Dec 2005 Location: New Zealand
Posts: 2,476
| As soon as you add the keyword virtual to your class, it's going to go up by the size of a pointer (on most compilers) because that's what the class needs added to it to implement the feature.
__________________ My homepage Advice: Take only as directed - If symptoms persist, please see your debugger |
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07-08-2009, 01:32 PM
| #6 | |
| Registered User Join Date: Mar 2009
Posts: 35
| Quote:
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07-08-2009, 02:13 PM
| #8 | |
| and the hat of sweating Join Date: Aug 2007 Location: Toronto, ON
Posts: 3,120
| Quote:
A doubt means you don't believe something is true. A question is when you are asking for an explanation about something that you're not sure of, and it usually ends with a question mark "?".
__________________ "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008 | |
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07-08-2009, 03:24 PM
| #9 |
| Guest  Join Date: Aug 2001
Posts: 4,923
| >> BTW, that is not a doubt, it's a question. Feeling a bit pedantistic today, are we?  |
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07-08-2009, 03:27 PM
| #10 | |
| and the Hat of Guessing  Join Date: Nov 2007
Posts: 8,740
| Quote:
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07-08-2009, 03:43 PM
| #11 |
| Guest Join Date: Aug 2001
Posts: 4,923
| >> ... must ... resist ... changing ... to ... "pedantic" ... grrrr .... Oh, the irony. Just to be sure, though (and yes I realize that I pretty much made that word up), I believe that is a legal (if not fugly) adjectivication of the word. Then again, English never was my best subject.  |
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07-08-2009, 08:09 PM
| #12 | |
| and the hat of sweating Join Date: Aug 2007 Location: Toronto, ON
Posts: 3,120
| Quote:
__________________ "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008 | |
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07-08-2009, 08:29 PM
| #13 |
| Guest Join Date: Aug 2001
Posts: 4,923
| >> Someone really has to find the dictionary that has that incorrect translation and burn it (and all copies of it). I remember my sister forcing me to read the entire dictionary due to my poor vocabulary. It actually helped quite a lot, but I'm still prone to make words up now and then. It may have something to do with the fact that I tend to break words up logically into roots and modifiers (not always correctly, either), so I often end up with words like 'pedantistic' or such.  |
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07-09-2009, 12:56 AM
| #14 | |
| Algorithm Dissector Join Date: Dec 2005 Location: New Zealand
Posts: 2,476
| Quote:
. | |
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07-09-2009, 06:55 AM
| #15 |
| and the hat of sweating Join Date: Aug 2007 Location: Toronto, ON
Posts: 3,120
|
__________________ "I am probably the laziest programmer on the planet, a fact with which anyone who has ever seen my code will agree." - esbo, 11/15/2008 |
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