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Unusual Q. for C++ Gurus !

Posted on 1997-08-05
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Last Modified: 2010-04-10
Hi !
When I create several objects of the same type, with the new operator indeed, I figure out each occurence has its own data area for obvious reasons, but what about the code area ? Do they share the same code section ? (in order to save memory).
I don't see any reason to duplicate the code of the objects, or am I missing something ?

Any ideas, comments, disapprovals ? Just wondering !
CU, have fun

p.s. this weird question was born after I made/took a bet with a mate ;-)
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Question by:ESI
12 Comments
 
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Author Comment

by:ESI
ID: 1166728
Edited text of question
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Expert Comment

by:AVaulin
ID: 1166729
You have to understand that code area is single for any objects number. First parameter of any class method in C++ is always pointer to object which need to call this method. That is why "this" pointer accessable in any class method.
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by:ESI
ID: 1166730
Hi AVaulin,
Ok, the address u point to with the 'this' ptr is in the data area of the object, different for each object indeed, but the code where the pointer is initialized is probably in the same code area, common to all object of a given class.
For example, if u have a sort rule in the code of a class, you think this code is duplicated with each instance of the class ?

Bye, and thanks 4 your time !
CU
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Expert Comment

by:TKII
ID: 1166731
ESI you got it completely right. The code is shared between all objects of the same class. It doesn't have to be this way but nothing else would make sense. Also it is said so in the Docs to VC++.
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Author Comment

by:ESI
ID: 1166732
Hi TKII !
Thanks 4 your reply.
Could u possibly point me to where u found some doc about this fact ? in the F1-Help ?

Bye, and thanks u 4 y'r precious time !
Cheers
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Author Comment

by:ESI
ID: 1166733
Is there any way to trace/show the PC main address counter of the CPU while debugging ? And to retrieve its value in C++ ?
(I'd like to write some self-modifying code)
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Expert Comment

by:mosfet
ID: 1166734
do you mean cs:ip??
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Author Comment

by:ESI
ID: 1166735
Hi mosfet,
Yes, I'd like copy in a C variable & use the CS:IP pointer.
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Author Comment

by:ESI
ID: 1166736
Hi mosfet,
Yes, I'd like copy in a C variable the CS:IP pointer.
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Expert Comment

by:alexxx
ID: 1166737
I suggest you try to write self-modifying code in Visual Basic. It's far more interesting, beleive me.
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Accepted Solution

by:
nigel5 earned 120 total points
ID: 1166738
The code segment is compiled from your source, including templates. This makes up the code segment, and is static throughout the life of the program. The heap is where objects are created dynamically and this memory is only used to store the class attributes, not the code. Global objects are compiled in, but again they all use the same code segment and the same functions.
You can take a function pointer of a class and call it like a standard function as long as you pass the object's address (the 'this' pointer) as the first  argument when you call it. Static functions do not pass the this pointer in as thay are not object specific.

In sumary....
there is only 1 copy of every function you write, templates will generate into 1 function per templated argument combination, and this code is available to all threads, and objects.

heap and stack can be independant within threads and process'.
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Author Comment

by:ESI
ID: 1166739
10x for your good explanation !. I get it now ;-)

Well, have happy programming & take care all !
Bye
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