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
