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Michael S.
Guest
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 Posted: Mon Dec 29, 2003 9:35 pm Post subject: Scope-problems |
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Hi
I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
So here's the question: what am I doing wrong and is there a way to
keep Xunode private while using it from Rep?
regards,
Michael
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Victor Bazarov
Guest
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| Posted: Tue Dec 30, 2003 12:08 am Post subject: Re: Scope-problems |
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"Michael S." <eyesshuttight (AT) web (DOT) de> wrote...
| Quote: | I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
So here's the question: what am I doing wrong and is there a way to
keep Xunode private while using it from Rep?
|
I think you got the friendship wrong. Only a friend of class A
can access A's private members. If you write a class B and then
declare that A is a friend of B, it does NOT make B a friend of
A automatically.
In your case, in order for 'Rep' to access 'Xunode', 'Rep' has
to be declared a friend of 'Xuint'.
Victor
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Wagner Bruna
Guest
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| Posted: Tue Dec 30, 2003 2:30 am Post subject: Re: Scope-problems |
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Hi,
[email]eyesshuttight (AT) web (DOT) de[/email] (Michael S.) wrote in message news:<b5aee4d3.0312291335.293c0da4 (AT) posting (DOT) google.com>...
| Quote: | Hi
I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
|
Yes, it should; I tested your code on Comeau online and gcc 3.2.3, and
it works fine.
| Quote: | So here's the question: what am I doing wrong and is there a way to
keep Xunode private while using it from Rep?
|
Hard to say, since it's compiler's fault... But you could use a
forward declaration to at least keep the implementation hidden:
class Xuint
{
public:
//listnode
struct Xunode;
private:
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
// (maybe) Xuint.cpp
struct Xuint::Xunode
{
unsigned short nodeval;
Xunode *next;
};
Or maybe you could declare Xunode inside Rep.
--
Wagner
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Jeff Schwab
Guest
|
| Posted: Tue Dec 30, 2003 3:26 am Post subject: Re: Scope-problems |
|
|
Wagner Bruna wrote:
| Quote: | Hi,
[email]eyesshuttight (AT) web (DOT) de[/email] (Michael S.) wrote in message news:<b5aee4d3.0312291335.293c0da4 (AT) posting (DOT) google.com>...
Hi
I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
Yes, it should; I tested your code on Comeau online and gcc 3.2.3, and
it works fine.
|
I believe this issue is covered by DR 45:
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_defects.html#45
Since Rep is a member of Xuint, it ought to have access to all the other
members (including Xunode). No friend declarations should be needed.
However, I believe Forte 5.4 is in compliance with the existing
standard. Do you have access to a newer version of the compiler?
-Jeff
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Michael S.
Guest
|
| Posted: Tue Dec 30, 2003 6:52 pm Post subject: Re: Scope-problems |
|
|
"Victor Bazarov" <v.Abazarov (AT) comAcast (DOT) net> wrote
| Quote: | "Michael S." <eyesshuttight (AT) web (DOT) de> wrote...
I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
So here's the question: what am I doing wrong and is there a way to
keep Xunode private while using it from Rep?
I think you got the friendship wrong. Only a friend of class A
can access A's private members. If you write a class B and then
declare that A is a friend of B, it does NOT make B a friend of
A automatically.
In your case, in order for 'Rep' to access 'Xunode', 'Rep' has
to be declared a friend of 'Xuint'.
Victor
|
You're right I really got that wrong, but when I insert a 'friend
class Rep;' into class Xuint I still get the same error.
Michael
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Michael S.
Guest
|
| Posted: Tue Dec 30, 2003 7:02 pm Post subject: Re: Scope-problems |
|
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Jeff Schwab <jeffplus (AT) comcast (DOT) net> wrote
| Quote: | Wagner Bruna wrote:
Hi,
[email]eyesshuttight (AT) web (DOT) de[/email] (Michael S.) wrote in message news:<b5aee4d3.0312291335.293c0da4 (AT) posting (DOT) google.com>...
Hi
I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
Yes, it should; I tested your code on Comeau online and gcc 3.2.3, and
it works fine.
I believe this issue is covered by DR 45:
http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/cwg_defects.html#45
Since Rep is a member of Xuint, it ought to have access to all the other
members (including Xunode). No friend declarations should be needed.
However, I believe Forte 5.4 is in compliance with the existing
standard. Do you have access to a newer version of the compiler?
-Jeff
No, I have to use that specific Compiler, because our prof insists on |
that one.
I thank all of you for your comments, but I think it will do little
harm if I make Xunode public, although I think from a stylistic point
of view it should be private.
regards,
Michael
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red floyd
Guest
|
| Posted: Wed Dec 31, 2003 12:59 am Post subject: Re: Scope-problems |
|
|
Michael S. wrote:
| Quote: | Hi
I'm having some problems with a class for large Integers (called
Xuint).
I want (have) to implement it like this:
- using a simple linked list
- a reference-objekt for each value, which means if 2 Xuint-objekts
have the same value, only one list is in memory and the 2
Xuint-objekts are pointing to the ref-objekt which points to the list.
By now I have this:
class Xuint
{
//listnode
struct Xunode{
unsigned short nodeval;
Xunode *next;
};
//ref-objekt
class Rep{
friend class Xuint;
Xunode *xustart;
int refs;
//...
};
public:
//...
};
When I compile this with Forte Developer C++ 5.4 I get:
"Error: Xuint::Xunode is not accessible from Xuint::Rep"
If I make Xunode public it works, but I don't understand why, because
from my point of view the 'friend class Xuint;' should make the
private parts of Xuint accessible to Rep.
|
Youve got it backwards. The friend declaration makes the private parts of Xuint::Rep available to Xuint.
What you need in Xuint is also a friend declaration:
friend class Xuint::Rep;
Because Xunode is private within Xuint, and Xuint::Rep has no special priviliges regarding Xuint, it can't see Xunode.
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