linking templates problem

[Tobias Langner]

I try to program a smart-pointer using policies. I rely heavyly on templates
during this. The program compiles fine - but I get a linker error:

test.o(.text+0x 3e): In function `testSmartPtr() ':
/home/tobias/project/Heart/heartofoak/test.cpp:23: undefined reference to
`SmartPtr<LongW rapper, RefCount>::Smar tPtr[in-charge](LongWrapper*)'
collect2: ld returned 1 exit status

I think the linker does not find the Constructor of the
SmartPointer<Lo ngWrapper, RefCount>.

The Code:

template <class T, template <class> class OwnershipPolicy >
class SmartPtr : public OwnershipPolicy <T> {
public:
explicit SmartPtr(T* pointer);
SmartPtr(const SmartPtr<T, OwnershipPolicy >& otherPointer);
SmartPtr& operator=(const SmartPtr<T, OwnershipPolicy >& otherSmartPtr);
~SmartPtr();
T& operator*() const;
T* operator->() const;

private:
void copyPtr(const SmartPtr<T, OwnershipPolicy >& otherPointer);
SmartPtr();
T* pointer_;

};

/* Policy Klassen fuer Kopien */
template <class T>
class RefCount {
private:
long *count_;
void initOwnership() ;
bool dispose();
bool copy(const SmartPtr<T, RefCount<T> >&);
friend class SmartPtr<T, RefCount>;
};

#include "smartptr.h "
#define DEBUG 1
#ifdef DEBUG
#include <iostream>
#endif

// not allowed, thus declared private and not implemented
template <class T, template <class> class OwnershipPolicy >
SmartPtr<T, OwnershipPolicy >::SmartPtr() {
}

template <class T, template <class> class OwnershipPolicy >
SmartPtr<T, OwnershipPolicy >::SmartPtr(T * pointer): pointer_(pointe r) {
#ifdef DEBUG
std::cout << "SmartPtr Constructor\n";
#endif
initOwnership() ;
}

template <class T, template <class> class OwnershipPolicy >
SmartPtr<T, OwnershipPolicy >::~SmartPtr( ){
#ifdef DEBUG
std::cout << "SmartPtr Destructor\n";
#endif
if (dispose() && pointer_!=NULL) {
delete pointer_;
}
}

template <class T, template <class> class OwnershipPolicy >
SmartPtr<T, OwnershipPolicy >::SmartPtr(con st SmartPtr<T, OwnershipPolicy >&
otherPointer) {
#ifdef DEBUG
std::cout << "SmartPtr Copy-Constructor\n";
#endif
copyPtr(otherPo inter);
}

template <class T, template <class> class OwnershipPolicy >
SmartPtr<T, OwnershipPolicy >& SmartPtr<T, OwnershipPolicy >::operator=(co nst
SmartPtr& otherSmartPtr) {
#ifdef DEBUG
std::cout << "SmartPtr Assignment Operator\n";
#endif
copyPtr(otherSm artPtr);
return *this;
}

template <class T, template <class> class OwnershipPolicy >
T& SmartPtr<T, OwnershipPolicy >::operator*( ) const {
return *pointer_;
}


template <class T, template <class> class OwnershipPolicy >
T* SmartPtr<T, OwnershipPolicy >::operator->() const {
return pointer_;
}

template <class T, template <class> class OwnershipPolicy >
void SmartPtr<T, OwnershipPolicy >::copyPtr(cons t SmartPtr<T,
OwnershipPolicy >& otherPointer) {
if (copy(otherPoin ter)) {
if (dispose() && pointer_!=NULL) {
delete pointer_;
}
}
pointer_=otherP ointer.pointer_ ;
}

template <class T>
bool RefCount<T>::co py(const SmartPtr<T, RefCount<T> >& otherPointer) {
#ifdef DEBUG
std::cout << "RefCount:: copy - count="<< (*count_) <<"\n";
#endif
count_=otherPoi nter.count_;
++(*count_);
return true;
}

template <class T>
void RefCount<T>::in itOwnership() {
count_=new long(1);
#ifdef DEBUG
std::cout << "RefCount::init Ownership - count="<< (*count_) <<"\n";
#endif
}

template <class T>
bool RefCount<T>::di spose() {
--(*count_);
#ifdef DEBUG
std::cout << "RefCount::disp ose - count="<< (*count_) <<"\n";
#endif
if (*count_==0) {
return true;
}
return false;
}

class LongWrapper {
private:
long x;
public:
LongWrapper(lon g l): x(l) {}

long get() { return x;}
};


bool testSmartPtr() {
LongWrapper *lp1=new LongWrapper(1);
/* HERE IS THE ERROR */
SmartPtr<LongWr apper, RefCount> *p1=new SmartPtr<LongWr apper,
RefCount>(lp1);


return true;
}

int main(int argc, char *argv[])
{
std::cout << "Hello, World!" << std::endl;

testSmartPtr();
return EXIT_SUCCESS;
}

[Victor Bazarov]

Re: linking templates problem

"Tobias Langner" <tobias.langner @t-online.de> wrote...[color=blue]
> I try to program a smart-pointer using policies. I rely heavyly on[/color]
templates[color=blue]
> during this. The program compiles fine - but I get a linker error:
>
> test.o(.text+0x 3e): In function `testSmartPtr() ':
> /home/tobias/project/Heart/heartofoak/test.cpp:23: undefined reference to[/color]
[...]

Place the template code in the header and next time start by
searching on http://groups.google.com. "template linker error
undefined reference" should have given you the answer way
before you could get this one.