Why am I getting this error ? "unresolved external symbol"

Question

This is the error I have been getting the whole time and I've been trying to figure out how to fix it but have failed. I am asking if anyone can point me to the right direction.

 WorldServer fatal error LNK1120: 2 unresolved externals
WorldServer error LNK2019: unresolved external symbol "public: class CItemElem * __thiscall CLinkedItemMgr::GetLinkedItem(unsigned long)" (?GetLinkedItem@CLinkedItemMgr@@QAEPAVCItemElem@@K@Z) referenced in function "private: void __thiscall CDPSrvr::OnLinkedItem(class CAr &,unsigned long,unsigned long,unsigned char *,unsigned long)" (?OnLinkedItem@CDPSrvr@@AAEXAAVCAr@@KKPAEK@Z)
WorldServer error LNK2019: unresolved external symbol "public: int __thiscall CLinkedItemMgr::AddLinkedItem(class CItemElem *)" (?AddLinkedItem@CLinkedItemMgr@@QAEHPAVCItemElem@@@Z) referenced in function "private: void __thiscall CDPSrvr::OnLinkedItem(class CAr &,unsigned long,unsigned long,unsigned char *,unsigned long)" (?OnLinkedItem@CDPSrvr@@AAEXAAVCAr@@KKPAEK@Z)

This is the .h

#ifndef __ITEM_LINK__H
#define __ITEM_LINK__H
class CLinkedItemMgr
{
private:
    CLinkedItemMgr(){ m_dwLinkedItemCount = 0;};
    ~CLinkedItemMgr(){};
    DWORD m_dwLinkedItemCount;
public:
    map<DWORD,CItemElem*> m_mapLinkedItems;

    static CLinkedItemMgr *GetInstance()
    {
        static CLinkedItemMgr instance;
        return &instance;
    }
    int AddLinkedItem(CItemElem *pItem);
    CItemElem *GetLinkedItem(DWORD dwIndex);
};
#endif

this is the .cpp

 #include "stdafx.h"
#include "ItemLink.h"
int CLinkedItemMgr::AddLinkedItem(CItemElem *pItem)
{
    if(!pItem)
        return 0;
    m_mapLinkedItems.insert(make_pair<DWORD,CItemElem*>(++m_dwLinkedItemCount,pItem));
    return m_dwLinkedItemCount;
}
CItemElem *CLinkedItemMgr::GetLinkedItem(DWORD dwIndex)
{
    map<DWORD,CItemElem*>::iterator it = m_mapLinkedItems.find(dwIndex);
    if(it == m_mapLinkedItems.end())
        return FALSE;
    return it->second;
}

Your include guards are reserved identifiers: http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier — chris, Mar 28 '13 at 20:13

Drew Dormann · Answer 1 · 2013-03-28T20:25:14.347

3

Your problem is in the cpp here.

#ifdef __ITEM_LINK
#include "ItemLink.h"

#ifdef __ITEM_LINK means "only process the code below if __ITEM_LINK is defined"

And in your case, it is not defined. It only gets defined when "ItemLink.h" is included, and "ItemLink.h" only gets included if it's already defined. You've prevented either from happening first.

Remove the #ifdef line.

edited Mar 28 '13 at 20:25

answered Mar 28 '13 at 20:13

Drew Dormann

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i've added the .cpp as well – user2205389 Mar 28 '13 at 20:18
alright thank you i will test it right now. – user2205389 Mar 28 '13 at 20:25
I removed the ifdef line but it seems I'm still getting the same error. – user2205389 Mar 28 '13 at 20:29
1

@user2205389 Please edit your question to show exactly what the code and error message look like now. – Drew Dormann Mar 28 '13 at 20:34
i pasted again the error but i'm pretty sure it was the same one as the old one. – user2205389 Mar 28 '13 at 20:38
i have edited it per your instructions. – user2205389 Mar 28 '13 at 20:50
@user2205389 I copied your new code and it builds successfully. I recommend visiting the link in the first comment to your question. – Drew Dormann Mar 28 '13 at 20:59
thank you for helping I was able to figure out the problem :) I appreciate the help – user2205389 Mar 28 '13 at 21:39

blue · Answer 2 · 2013-03-28T21:01:25.130

0

It looks like a linking problem. The compiler knows your class has a function called GetLinkedItem but can't find any definition of that function anywhere. Are you linking properly when compiling your executable? I bet stopping the compiler before linking doesn't trigger any error. (e.g. g++ -c ItemLink.cpp).

i'm going to ask the help of someone who's accustomed to visual studio to elaborate more :D anyway, compiling requires three major steps: 1) applying preprocessor directives, parsing the source code, looking for syntax errors and the like 2) creating an object file from source code (something half-way between source code and executable) 3) linking all the object files making up your project in one executable

your compiling chain fails at the third step. the compiler expects a certain function to be defined in some .cpp (that has become an object file at step 2 of compiling chain) but can't find it anywhere.

and it can't find it because of that #ifdef in the .cpp file, which tells the preprocessor NOT TO INCLUDE your definitions, since __ITEM_LINK is not defined

i see you changed the .cpp in your question by the way

edited Mar 28 '13 at 21:01

answered Mar 28 '13 at 20:23

blue

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Mind eplaining to me what you mean by stopping the compiler? I'm using Visual Studio 2003 – user2205389 Mar 28 '13 at 20:31
i elaborated more in my answer, hope you find it helpful – blue Mar 28 '13 at 21:01
Alright I'll check to see if i missed anywhere on defining ITEM_LINK – user2205389 Mar 28 '13 at 21:13
The code displayed in your question should compile, though, since those #ifndefs have been removed. Does it? – blue Mar 28 '13 at 21:16
thank you for helping I was able to figure out the problem :) I appreciate the help – user2205389 Mar 28 '13 at 21:39
what about an up for me? :D – blue Mar 29 '13 at 00:54
sorry I don't have enough votes to do that. :) – user2205389 Mar 29 '13 at 02:44

Why am I getting this error ? "unresolved external symbol"

2 Answers2

Linked