I have an MFC app which is a semestral final project at the university. The project’s solution includes two DLL modules: Except1 (handling errors and displaying messages), MyData (managing application data) and ProjectMFC that compiles to .exe file (the proper application project).
The project’s dependencies look like below:

Except1
|
|-->MyData
|     |
|     v
|-->ProjectMFC

According to the project guidelines in MyData and ProjectMFC files I have to create a declaration of pointer to Except1 module’s class in order to use methods from this module.

CExcept1App* pExcept;

In ProjectMFC it works.
But in MyData I get a linker error

Error LNK2019 unresolved external symbol GetExceptPtr referenced in function "public: __cdecl MY_DATA::MY_DATA(int)" (??0MY_DATA@@QEAA@H@Z)
although I’ve added additional dependencies in MyData project’s properties.

MyData.h:

// MyData.h : main header file for the MyData DLL
//

#pragma once

#ifndef __AFXWIN_H__
    #error "include 'pch.h' before including this file for PCH"
#endif

#include "resource.h"       // main symbols
#include "Except1.h"

#ifdef MY_DATA_EXPORTS
#define MYDATA_API __declspec(dllexport)
#else
#define MYDATA_API __declspec(dllimport)
#endif // MY_DATA_EXPORTS

// CMyDataApp
// See MyData.cpp for the implementation of this class
//

//template <class T, class Key>
//T* find(const T* p_begin, const T* p_end, const Key& k)
//{
//  if (p_begin >= p_end)
//      return NULL;
//
//  T* p_tmp = const_cast<T*>(p_begin);
//  for (; p_tmp != p_end; p_tmp++)
//  {
//      if (*p_tmp == key)
//          return p_tmp;
//  }
//  return NULL;
//}

class CMyDataApp : public CWinApp
{
public:
    CMyDataApp();

// Overrides
public:
    virtual BOOL InitInstance();

    DECLARE_MESSAGE_MAP()
};

class CExcept1App;

class MYDATA_API MY_POINT
{
public:
    double x;
    double y;
    char* name = NULL;
    COLORREF color;

    MY_POINT() : x(0), y(0), name(NULL), color(RGB(0, 0, 0)){}
    MY_POINT(double xx, double yy, COLORREF c_color, const char* nname);
    MY_POINT(const MY_POINT& ob);
    ~MY_POINT() 
    { 
        if (name) 
            delete[] name;
        name = NULL;
    }

    MY_POINT& operator=(const MY_POINT& ob);
    void set(double xx, double yy, COLORREF c_color, const char* nname);
    MY_POINT get() { return *this; }

};

class MYDATA_API MY_DATA : public MY_POINT
{
protected:
    MY_POINT* pTab;
    int capacity;
    int last;
public:
    CExcept1App* pExcept;
    MY_DATA(int no_it);
    MY_DATA(const MY_DATA& ob);
    ~MY_DATA() { Free(); }
    int size() { return last; }
    void Free() { if (pTab) delete[] pTab; pTab = NULL; }
    void Init(int no_it);
    void Push(const MY_POINT& tmp);
    int Size() { return last; }
    void clear() { last = 0; }

    MY_POINT& operator [] (const int i) {
        return pTab[i];
    }
    void GetMaxMinCoords(double& max_x, double& min_x, double& max_y, double& min_y);


private:
    MY_POINT* allocTab(MY_POINT* pTab, int n);
};

MyData.cpp:

// MyData.cpp : Defines the initialization routines for the DLL.
//

#include "pch.h"
#include "framework.h"
#include "MyData.h"

#include <iostream>

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

// CMyDataApp

BEGIN_MESSAGE_MAP(CMyDataApp, CWinApp)
END_MESSAGE_MAP()


// CMyDataApp construction

CMyDataApp::CMyDataApp()
{
    // TODO: add construction code here,
    // Place all significant initialization in InitInstance
}


// The one and only CMyDataApp object

CMyDataApp theApp;

// CMyDataApp initialization

BOOL CMyDataApp::InitInstance()
{
    CWinApp::InitInstance();

    return TRUE;
}

MY_POINT::MY_POINT(double xx, double yy, COLORREF c_color, const char* nname = nullptr) : x(xx), y(yy), color(c_color)
{
    try
    {
        if (name)
        {
            name = new char[strlen(nname) + 1];
            strcpy_s(name, strlen(nname) + 1, nname);
        }
    }
    catch (std::bad_alloc)
    {
        //pExcept->PutMessage(1001);
        name = NULL;
    }
}

MY_POINT::MY_POINT(const MY_POINT& ob)
{
    x = ob.x;
    y = ob.y;
    color = ob.color;

    try
    {
        if (ob.name)
        {
            name = new char[strlen(ob.name) + 1];
            strcpy_s(name, strlen(ob.name) + 1, ob.name);
        }
    }
    catch (std::bad_alloc)
    {
        //pExcept->PutMessage(1001);
        name = NULL;
    }
}

MY_POINT& MY_POINT::operator=(const MY_POINT& ob)
{
    if (this == &ob) return *this;

    delete[] name;
    name = NULL;

    x = ob.x;
    y = ob.y;
    color = ob.color;
    try
    {
        if (ob.name)
        {
            name = new char[strlen(ob.name) + 1];
            strcpy_s(name, strlen(ob.name) + 1, ob.name);
        }
    }
    catch (std::bad_alloc)
    {
        //pExcept->PutMessage(1001);
        name = NULL;
    }
    
    return *this;
}

void MY_POINT::set(double xx, double yy, COLORREF c_color, const char* nname)
{
    x = xx;
    y = yy;
    color = c_color;

    delete[] name;
    name = NULL;

    try
    {
        if (name)
        {
            name = new char[strlen(nname) + 1];
            strcpy_s(name, strlen(name) + 1, nname);
        }
    }
    catch (std::bad_alloc)
    {
        //pExcept->PutMessage(1001);
        name = NULL;
    }
}

MY_DATA::MY_DATA(int no_it)
{
    pExcept = GetExceptPtr();
    pTab = NULL;
    Init(no_it);
}

MY_POINT* MY_DATA::allocTab(MY_POINT* pTab, int n)
{
    try
    {
        if (!pTab)
        {
            pTab = new MY_POINT[n];
            capacity = n;
        }
    }
    catch (std::bad_alloc aa)
    {
        //pExcept->PutMessage(1001);
    }
    return pTab;
}
//it's the part of code using pExcept pointer

Except1.h:

// Except1.h : main header file for the Except1 DLL
//

#pragma once

#ifndef __AFXWIN_H__
    #error "include 'pch.h' before including this file for PCH"
#endif

#include "resource.h"       // main symbols

#ifdef EXCEPT1_EXPORT
#define EXCEPT1_API __declspec(dllexport)
#else
#define EXCEPT1_API __declspec(dllimport)
#endif

// CExcept1App
// See Except1.cpp for the implementation of this class
//

#define APP_START_MESSAGE WM_USER+100

enum ITS_APP_MESSAGE
{
    WM_START = APP_START_MESSAGE,
    WM_DIS_MSG,
    WM_CLEAR_OUTPUT,
    WM_DIS_TOTALMES
};

class MY_DATA;

class EXCEPT1_API CExcept1App : public CWinApp
{
public:
    CWnd* ptrWnd;
    MY_DATA* ptrDat;

public:
    CExcept1App();
    void SetWnd(CWnd* ptrwnd, MY_DATA* pdat) { ptrWnd = ptrwnd; ptrDat = pdat; }
    void ResetDat(MY_DATA* pdat) { ptrDat = pdat; }
    void PutMessage(UINT ID_MESSAGE);
    void ClearOutWnd();

// Overrides
public:
    virtual BOOL InitInstance();

    DECLARE_MESSAGE_MAP()
};

extern "C" CExcept1App * PASCAL EXPORT GetExceptPtr();```

GetExceptPtr() is also in Except1.def file:

; Except1.def : Declares the module parameters for the DLL.

LIBRARY

EXPORTS
; Explicit exports can go here
GetExceptPtr

Except1.cpp:
// Except1.cpp : Defines the initialization routines for the DLL.
//

#include "pch.h"
#include "framework.h"
#include "Except1.h"

#ifdef _DEBUG
#define new DEBUG_NEW
#endif

// CExcept1App

BEGIN_MESSAGE_MAP(CExcept1App, CWinApp)
END_MESSAGE_MAP()


// CExcept1App construction

CExcept1App::CExcept1App()
{
    // TODO: add construction code here,
    // Place all significant initialization in InitInstance
    ptrWnd = NULL;
    ptrDat = NULL;
}


// The one and only CExcept1App object

CExcept1App theApp;


// CExcept1App initialization

BOOL CExcept1App::InitInstance()
{
    CWinApp::InitInstance();

    return TRUE;
}


void CExcept1App::PutMessage(UINT ID_Message)
{
    HINSTANCE hInstance = GetModuleHandleA(NULL);
    char str[1024];
    int ret = LoadStringA(hInstance, ID_Message, str, sizeof(str));
    if (ptrWnd)
        ptrWnd->SendMessage(WM_DIS_MSG, (WPARAM)str, (LPARAM)ptrDat);
    else if (!ptrWnd && str[0] == 'E')
    {
        CString sstr(str);
        AfxMessageBox(sstr);
        UINT uExitCode = 0;
        HANDLE hHandle = GetCurrentProcess();
        TerminateProcess(GetCurrentProcess(), uExitCode);
    }
}

void CExcept1App::ClearOutWnd()
{
    if (ptrWnd)
        ptrWnd->SendMessage(WM_CLEAR_OUTPUT, 0, 0);
}

extern "C" CExcept1App * PASCAL EXPORT GetExceptPtr()
{
    AFX_MANAGE_STATE(AfxGetStaticModuleState());
    return &theApp;
}



I've tried to use forward declaration because both Except1 and MyData use their pointers but it didn't solve the problem.