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Draw the memory layout of a C++ class with two virtual functions

Posted on 2006-07-11
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It's an interview question. Any help is appreciated.

Thanks!
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Question by:gromul
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3 Comments
 
LVL 86

Accepted Solution

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jkr earned 2000 total points
ID: 17085339
See http://en.wikipedia.org/wiki/Virtual_method_table

Assuming

class foo {

public:

virtual void f1();
virtual void f2();

};

foo:
  +0: pointer to virtual method table of foo

Basically, it is only the pointer to the VTABLE if the class has no other (data) members - 4 bytes, that's it.

If you have

class foo {

public:

virtual void f1();
virtual void f2();

int n;
};

that'd be

  +0: pointer to virtual method table of foo
  +4: value of 'n'
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Expert Comment

by:dbkruger
ID: 17085513
This is only a possible implementation, though it's extremely common, so I'd avoid saying this is THE layout.
It's conceivable that on some weird architecture they could do something else.

Good luck
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LVL 4

Expert Comment

by:havman56
ID: 17097381
JKR  thanks for the link fom wikipedia

i learnt lot abt vtable  !!
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