public inbox for gcc-bugs@sourceware.org
help / color / mirror / Atom feed
* [Bug c++/19188] New: friend funtion inside a template class seems to have a problem
@ 2004-12-29 13:47 max656 at hotmail dot com
2004-12-29 14:21 ` [Bug c++/19188] " lerdsuwa at gcc dot gnu dot org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: max656 at hotmail dot com @ 2004-12-29 13:47 UTC (permalink / raw)
To: gcc-bugs
A template class(tstack class) has a singly-linked list "struct" declaration in
private section.
Another template class(tstackIterator) - iterator class is declared and defined
in global space.
If the iterator template class trys to get access to the linked list structure
inside the previous class with a friend statement declared in the previous
class, it does not work. It behaves in much the same way as without friend
declaration. The following code shows this:
//: TSTACK.H -- Stack using templates
#ifndef TSTACK_H_
#define TSTACK_H_
// Some implementations require this:
template<class T> class tstackIterator;
template<class T>
class tstack {
struct link {
T* data;
link* next;
link(T* Data, link* Next){
data = Data;
next = Next;
}
} * head;
int owns;
public:
tstack(int Owns = 1) : head(0), owns(Owns) {}
~tstack();
void push(T* Data) {
head = new link(Data,head);
}
T* peek() const { return head->data; }
T* pop();
int Owns() const { return owns; }
void Owns(int newownership) {
owns = newownership;
}
friend class tstackIterator<T>;
};
template<class T>
T* tstack<T>::pop() {
if(head == 0) return 0;
T* result = head->data;
link* oldHead = head;
head = head->next;
delete oldHead;
return result;
}
template<class T>
tstack<T>::~tstack() {
link* cursor = head;
while(head) {
cursor = cursor->next;
// Conditional cleanup of data:
if(owns) delete head->data;
delete head;
head = cursor;
}
}
template<class T>
class tstackIterator {
////////////////////////////////////
tstack<T>::link* p; // this is line 68
// when it is compiled, g++ 3.4.1 give some error message but it does not make
//sense in terms of languae. but the version g++ (GCC) 3.2.3 20030502 works fine
// except that it gives a warning saying "tstack.h:68: warning: `typename
//tstack<T>::link' is implicitly a typename"
//The Error message is attached to the bottom
///////////////////////////////////
public:
tstackIterator(const tstack<T>& tl)
: p(tl.head) {}
tstackIterator(const tstackIterator& tl)
: p(tl.p) {}
// operator++ returns boolean indicating end:
int operator++() {
if(p->next)
p = p->next;
else p = 0; // Indicates end of list
return int(p);
}
int operator++(int) { return operator++(); }
// Smart pointer:
T* operator->() const {
if(!p) return 0;
return p->data;
}
T* current() const {
if(!p) return 0;
return p->data;
}
// int conversion for conditional test:
operator int() const { return p ? 1 : 0; }
};
#endif // TSTACK_H_
////////////////////////////////////////////
the compiler complaints are as follows:
In file included from tstktst.cpp:2:
../14/tstack.h:68: error: expected `;' before '*' token
../14/tstack.h: In constructor `tstackIterator<T>::tstackIterator(const
tstack<T>&)':
../14/tstack.h:71: error: class `tstackIterator<T>' does not have any field
named `p'
../14/tstack.h: In copy constructor `tstackIterator<T>::tstackIterator(const
tstackIterator<T>&)':
../14/tstack.h:73: error: class `tstackIterator<T>' does not have any field
named `p'
../14/tstack.h: In member function `int tstackIterator<T>::operator++()':
../14/tstack.h:76: error: `p' undeclared (first use this function)
../14/tstack.h:76: error: (Each undeclared identifier is reported only once for
each function it appears in.)
../14/tstack.h: In member function `T* tstackIterator<T>::operator->() const':
../14/tstack.h:84: error: `p' undeclared (first use this function)
../14/tstack.h: In member function `T* tstackIterator<T>::current() const':
../14/tstack.h:88: error: `p' undeclared (first use this function)
../14/tstack.h: In member function `tstackIterator<T>::operator int() const':
../14/tstack.h:92: error: `p' undeclared (first use this function)
--
Summary: friend funtion inside a template class seems to have a
problem
Product: gcc
Version: 3.4.1
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: max656 at hotmail dot com
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19188
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/19188] friend funtion inside a template class seems to have a problem
2004-12-29 13:47 [Bug c++/19188] New: friend funtion inside a template class seems to have a problem max656 at hotmail dot com
@ 2004-12-29 14:21 ` lerdsuwa at gcc dot gnu dot org
2004-12-30 7:41 ` max656 at hotmail dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: lerdsuwa at gcc dot gnu dot org @ 2004-12-29 14:21 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From lerdsuwa at gcc dot gnu dot org 2004-12-29 14:20 -------
Not a bug. You have to replace the code at line 68:
tstack<T>::link* p;
with
typename tstack<T>::link* p;
Check out the web page <http://gcc.gnu.org/gcc-3.4/changes.html>
and search for "You mustnow use the typename and template" ...
for more information. There have been a lot of changes to the
C++ language since the old days and this is one of them.
--
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19188
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/19188] friend funtion inside a template class seems to have a problem
2004-12-29 13:47 [Bug c++/19188] New: friend funtion inside a template class seems to have a problem max656 at hotmail dot com
2004-12-29 14:21 ` [Bug c++/19188] " lerdsuwa at gcc dot gnu dot org
@ 2004-12-30 7:41 ` max656 at hotmail dot com
2004-12-31 13:23 ` lerdsuwa at gcc dot gnu dot org
2005-01-01 1:37 ` max656 at hotmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: max656 at hotmail dot com @ 2004-12-30 7:41 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From max656 at hotmail dot com 2004-12-30 07:41 -------
Thanks for the reply.
In this one line of code
tstack<T>::link* p;
"tstack<T>::link " is a typename. so I can not give another name.
Actually, I got other ways to get around this problem.
But I am interested in this style as well.
The code I am experimenting came from Bruce Eckel's old book.
The 2nd edtion uses a different way from this.
Anyway the definition of "tstack<T>::link" is not created inside the class. it
is used only to declare a private pointer variable named "head".Actually it is
NOT defined. I think that's why g++ (GCC) 3.2.3 20030502 give the warning of
"implicite typename". But a new version, g++ 3.4.1, checks it out and send out a
error message of "../14/tstack.h:68: error: expected `;' before '*' token". I
don't have any idea of what this means. It does not make any sense at all.
Would you take a look at it and reply to me ?
I really appreciate it in advance.
Tyson
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19188
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/19188] friend funtion inside a template class seems to have a problem
2004-12-29 13:47 [Bug c++/19188] New: friend funtion inside a template class seems to have a problem max656 at hotmail dot com
2004-12-29 14:21 ` [Bug c++/19188] " lerdsuwa at gcc dot gnu dot org
2004-12-30 7:41 ` max656 at hotmail dot com
@ 2004-12-31 13:23 ` lerdsuwa at gcc dot gnu dot org
2005-01-01 1:37 ` max656 at hotmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: lerdsuwa at gcc dot gnu dot org @ 2004-12-31 13:23 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From lerdsuwa at gcc dot gnu dot org 2004-12-31 13:23 -------
The 'typename' keyword is required because later C++ introduces a lot more
features. Those that interfere with your code are partial specialization
and specialization. For example, you can now have specialization
template <> class tstack<bool> {
int link;
...
};
Then when you declare
tstack<bool> t;
it will use the above declaration, where 'link' is now a member data
instead of a nested class. So the code
tstack<T>::link* p;
which could be interpreted as declaring a variable which is a pointer to type
'tstack<T>::link' if 'T' is 'int'. But when 'T' is 'bool' it could means
multiplying a member data with another variable named 'p'.
To resolve the ambiguity, later C++ requires the 'typename' keyword to
treat as pointer declaration, otherwise it will be treated as muliplication.
Older C++ books don't have this 'typename' keyword but newer good books
from respected authors coming out in the last few years should.
(Many new C++ books are still wrong).
I know the parser error message could be improved, and there are plenty of
bug reports elsewhere about it.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19188
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/19188] friend funtion inside a template class seems to have a problem
2004-12-29 13:47 [Bug c++/19188] New: friend funtion inside a template class seems to have a problem max656 at hotmail dot com
` (2 preceding siblings ...)
2004-12-31 13:23 ` lerdsuwa at gcc dot gnu dot org
@ 2005-01-01 1:37 ` max656 at hotmail dot com
3 siblings, 0 replies; 5+ messages in thread
From: max656 at hotmail dot com @ 2005-01-01 1:37 UTC (permalink / raw)
To: gcc-bugs
------- Additional Comments From max656 at hotmail dot com 2005-01-01 01:37 -------
Subject: RE: friend funtion inside a template class seems to have a probl
Hi lerdsuwa
You came up with an interesting topic - class template specializtion.
I didn't know aboou it. I need further research on that.
As you mentioned, the keyword "typename' is added and compiled and then it
works fine.
Thanks a lot for your detailed explanation.
It haunted me a lot. I was completely stuck for a while even though I found
some other ways.
Tyson
>From: "lerdsuwa at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>
>Reply-To: gcc-bugzilla@gcc.gnu.org
>To: max656@hotmail.com
>Subject: [Bug c++/19188] friend funtion inside a template class seems to
>have a problem
>Date: 31 Dec 2004 13:23:03 -0000
>
>------- Additional Comments From lerdsuwa at gcc dot gnu dot org
>2004-12-31 13:23 -------
>The 'typename' keyword is required because later C++ introduces a lot more
>features. Those that interfere with your code are partial specialization
>and specialization. For example, you can now have specialization
>
> template <> class tstack<bool> {
> int link;
> ...
> };
>
>Then when you declare
>
> tstack<bool> t;
>
>it will use the above declaration, where 'link' is now a member data
>instead of a nested class. So the code
>
> tstack<T>::link* p;
>
>which could be interpreted as declaring a variable which is a pointer to
>type
>'tstack<T>::link' if 'T' is 'int'. But when 'T' is 'bool' it could means
>multiplying a member data with another variable named 'p'.
>
>To resolve the ambiguity, later C++ requires the 'typename' keyword to
>treat as pointer declaration, otherwise it will be treated as
>muliplication.
>Older C++ books don't have this 'typename' keyword but newer good books
>from respected authors coming out in the last few years should.
>(Many new C++ books are still wrong).
>
>I know the parser error message could be improved, and there are plenty of
>bug reports elsewhere about it.
>
>--
>
>
>http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19188
>
>------- You are receiving this mail because: -------
>You reported the bug, or are watching the reporter.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19188
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2005-01-01 1:37 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2004-12-29 13:47 [Bug c++/19188] New: friend funtion inside a template class seems to have a problem max656 at hotmail dot com
2004-12-29 14:21 ` [Bug c++/19188] " lerdsuwa at gcc dot gnu dot org
2004-12-30 7:41 ` max656 at hotmail dot com
2004-12-31 13:23 ` lerdsuwa at gcc dot gnu dot org
2005-01-01 1:37 ` max656 at hotmail dot com
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).