1

I don't know why: When declarations and definitions are not separated from the block's class(class SLinkedList{ ....}). The building will be successful.

But when I separate declarations and definitions of the class below. The building will report an error like this

"Severity Code Description Project File Line Suppression State Error LNK2019 unresolved external symbol "public: __thiscall SLinkList<char>::SLinkList<char>(void)" (??0?$SLinkList@D@@QAE@XZ) referenced in function _main LinkedLists C:\Users\LQA\Documents\Visual Studio 2015\Projects\DataStructures\DataStructures\Source.obj 1"

This is the detail source code: [LinkedLists.h]

#include <iostream>
#include <string>
using namespace std;


//Singly Linked List

template<typename E>
class SLinkList;

template<typename E>
class SNode
{
private:
    E elem;
    SNode<E>* next;
    friend class SLinkList<E>;
};

template<typename E>
class SLinkList
{
public:
    SLinkList();
    ~SLinkList();
    bool empty() const;
    const E& front() const;
    void addFront(const E& e);
    void removeFront();
private:
    SNode<E>* head;
};

[LinkedLists.cpp]

#include "LinkedLists.h"


/*
 * SINGLY LINKED LIST
 */
template<typename E>
SLinkList<E>::SLinkList() :
    head(NULL) {}

template<typename E>
SLinkList<E>::~SLinkList()
{
    while (!this->empty())
    {
        removeFront();
    }
}

template<typename E>
bool SLinkList<E>::empty() const
{
    return head == NULL;
}

template<typename E>
const E& SLinkList<E>::front() const
{
    return this->head->elem;
}

template<typename E>
void SLinkList<E>::removeFront()
{
    SNode<E>* old = this->head;
    this->head = old->next;
    delete old;
}

template<typename E>
void SLinkList<E>::addFront(const E& e)
{
    SNode<E>* v = new SNode<E>;
    v->elem = e;
    v->next = this->head;
    this->head = v;
}

[Source.cpp]

#include "LinkedLists.h"
using namespace std;

int main(void)
{
    SLinkList<char>* llst = new SLinkList<char>();
    //llst->addFront('a');
    //llst->addFront('b');
    return 0;
}

Does anyone know what was caused to this problem?

acraig5075
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LPA1HC
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2 Answers2

0

Did you try to add "__declspec(dllexport)" before the class declaration in h file?

As soon as you move class function members definition to separate cpp file, then you need to add this specifier in order to make all that definitions visible outside the dll.

dusan.stanivukovic
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  • I had tried to add __declspec(dllexport) macro. The VS 2015 had generated a *.dll file. But when I used another project and linked to the *.dll, It still reported that error. If you can make it to build successfully. Can you share me how to make it. – LPA1HC Aug 29 '18 at 02:24
  • You can try to inspect the dll with tool Dependency Walker, to actually see if those functions are exported or not. – dusan.stanivukovic Aug 29 '18 at 19:34
0

If you declare template class in c++, you should include function body to header file.

for example: [LinkedLists.h]

...
template<typename E>
class SLinkList
{
public:
    SLinkList() : head(NULL) {};
    ~SLinkList() 
    {
        while (!this->empty())
        {
            removeFront();
        }
    };

    bool empty() const
    {
        return head == NULL;
    }
...
Ahn SeungRye
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