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+0x3e): In function `testSmartPtr()':
/home/tobias/project/Heart/heartofoak/test.cpp:23: undefined reference to
`SmartPtr<LongWrapper, RefCount>::SmartPtr[in-charge](LongWrapper*)'
collect2: ld returned 1 exit status

I think the linker does not find the Constructor of the
SmartPointer<LongWrapper, 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_(pointer) {
#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(const SmartPtr<T, OwnershipPolicy>&
otherPointer) {
#ifdef DEBUG
std::cout << "SmartPtr Copy-Constructor\n";
#endif
copyPtr(otherPointer);
}

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

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


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

template <class T, template <class> class OwnershipPolicy>
void SmartPtr<T, OwnershipPolicy>::copyPtr(const SmartPtr<T,
OwnershipPolicy>& otherPointer) {
if (copy(otherPointer)) {
if (dispose() && pointer_!=NULL) {
delete pointer_;
}
}
pointer_=otherPointer.pointer_;
}

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

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

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

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

long get() { return x;}
};


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


return true;
}

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

testSmartPtr();
return EXIT_SUCCESS;
}

 

[Victor Bazarov]

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+0x3e): In function `testSmartPtr()':
/home/tobias/project/Heart/heartofoak/test.cpp:23: undefined reference to

[...]

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.