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Topic: Where are C++ gurus, also elab. on below quest. (Read 700 times) |
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puzzlecracker
Senior Riddler
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Where are C++ gurus, also elab. on below quest.
« on: Jan 10th, 2005, 5:14pm » |
 Quote  Modify
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WHat is the difference between?
a)
class base {
public:
base();
~base();
void virtual func_1();
:
:
void virtual func_n();
};
class derived:public base{
public:
derived();
~derived();
void virtual func_1()
:
:
void virtual func_n();
};
vs.
b)
class base {
public:
base();
~base();
void virtual func_1();
:
:
void virtual func_n();
};
class derived: virtual public base{
public:
derived();
~derived();
void virtual func_1()
:
:
void virtual func_n();
};
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TenaliRaman
Uberpuzzler
I am no special. I am only passionately curious.
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Posts: 1001
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Re: Where are C++ gurus, also elab. on below quest
« Reply #1 on: Jan 10th, 2005, 11:06pm » |
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I will give u a small hint.
Let us say that we have four classes class A,B,C,D such that :
Class B and Class C are derived from class A
Class D is derived from Class B and Class C.
Do u see any problem here?
-- AI
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| « Last Edit: Jan 10th, 2005, 11:07pm by TenaliRaman » |
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puzzlecracker
Senior Riddler
Men have become the tools of their tools
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Posts: 319
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Re: Where are C++ gurus, also elab. on below quest
« Reply #2 on: Jan 10th, 2005, 11:10pm » |
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I know about this diamond problem clotted with ambiguity due to methods/variables duplicates; I am more interested as to how it works to prevent that
thx
... cracker
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TenaliRaman
Uberpuzzler
I am no special. I am only passionately curious.
Gender:
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Re: Where are C++ gurus, also elab. on below quest
« Reply #3 on: Jan 11th, 2005, 5:54am » |
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This is straight from ANSI C++ Handbook
How does C++ ensure that only a single instance of a virtual member exists, regardless of the number of classes derived from it? This is implementation-dependent. However, all implementations currently use an additional level of indirection to access a virtual base class, usually by means of pointer.
//Note: this is a simplified description of iostream classes
class ostream: virtual public ios { /*..*/ }
class istream: virtual public ios { /*..*/ }
class iostream : public istream, public ostream { /*..*/ }
In other words, each object in the iostream hierarchy has a pointer to the shared instance of the ios subobject. The additional level of indirection has a slight performance overhead. It also implies that the location of virtual subobjects is not known at compile time; therefore, RTTI (RunTime Type Identification) might be needed to access virtual subobjects in some circumstances.
When multiple inheritance is used, the memory layout of such an object is implementation-dependent. The compiler can rearrange the order of the inherited subobjects to improve memory alignment. In addition, a virtual base can be moved to a different memory location. Therefore, when you are using multiple inheritance, do not assume anything about the underlying memory layout of an object.
-- AI
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| « Last Edit: Jan 11th, 2005, 5:56am by TenaliRaman » |
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