Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" (аргументы) As Long

Public Declare Function CPP_MyFunction Lib "C:\MyKnownPath\cpp_my_dll.dll" (аргументы) As Long

hMod = LoadLibrary("SomePath\cpp_my_dll.dll")
ProcAdd = GetProcAddress(hMod, "CPP_MyFunction")

??????????????????
...
FreeLibrary hMod

typedef int (__cdecl *MYPROC)();

ProcAdd = (MYPROC) GetProcAddress(hinstLib, "CPP_MyFunction"); 
(ProcAdd) (); 

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long

Public Function My_MyFunction(ByVal PathToDll As String) As String
  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = LoadLibrary(PathToDll)
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction")
    If ProcAdd <> 0 Then
      My_MyFunction = PtrToString(CallWindowProc(ProcAdd, 0, 0, 0, 0))
    End If
    FreeLibrary hMod
  End If
End Function

CallWindowProc(ProcAdd, 0, 0, 0, 0)

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long

Public Function MyLoad_MyFunction_1(ByVal PathOnlyToDll As String) As String
  'PathOnlyToDll -только Folder ее нахождения
  SetDllDirectory PathOnlyToDll '!!!SetDllDirectory не проверяет даже существование папки
  MyLoad_MyFunction_1= PtrToString(CPP_MyFunction)
End Function

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long

Public Function MyLoad_MyFunction_2(ByVal PathToDll As String) As String
  Dim hMod As Long
  hMod = LoadLibrary(PathToDll)
  If hMod <> 0 Then
    MyLoad_MyFunction_2= PtrToString(CPP_MyFunction)
    Dim FreeResult As Long
    FreeResult = 1
    Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
      FreeResult = FreeLibrary(hMod)
      Debug.Print FreeResult
    Loop
  End If
End Function

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long 'путь не указываем

Public Function MyLoad_MyFunction(ByVal PathToDll As String) As String
  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = LoadLibrary(PathToDll)
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction")
    If ProcAdd <> 0 Then
      MyLoad_MyFunction= PtrToString(CPP_MyFunction) 'а не по ProcAdd!!!
    End If
    Dim FreeResult As Long
    FreeResult = 1
    Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
      FreeResult = FreeLibrary(hMod)
      Debug.Print FreeResult
    Loop
  End If
End Function

typedef
BOOL
(*PINSTALLSELECTEDDRIVER)(
  HWND hwndParent,
  HDEVINFO DeviceInfoSet,
  LPCWSTR Reserved,
  BOOL Backup,
  PDWORD pReboot    
  );

    // To be more secure, make sure to load the newdev.dll file from the
    // system 32 directory.
    if (GetSystemDirectory(NewDevPath, SIZECHARS(NewDevPath)) == 0) {
      DisplayError(_T("GetSystemDirectory"));
      goto ForceInstall;
    }

    if (FAILED(StringCchCat(NewDevPath, SIZECHARS(NewDevPath), TEXT("\\NEWDEV.DLL")))) {
      SetLastError(ERROR_INSUFFICIENT_BUFFER);
      DisplayError(_T("StringCchCat"));
      goto ForceInstall;
    }

    hNewDev = LoadLibrary(NewDevPath);
    if (!hNewDev) {
      DisplayError(_T("LoadLibrary"));
      goto ForceInstall;
    }

    pInstallSelectedDriver = (PINSTALLSELECTEDDRIVER)GetProcAddress(hNewDev, "InstallSelectedDriver");
    if (!pInstallSelectedDriver) {
      DisplayError(_T("GetProcAddress"));
      goto ForceInstall;
    }

    // Call pInstallSelectedDriver to install the selected driver on
    // the selected device.
    if (!pInstallSelectedDriver(NULL,
                           DeviceInfoSet,
                           NULL,
                           FALSE,
                           &dwRebootRequired)) {
      DisplayError(_T("InstallSelectedDriver"));
      goto ForceInstall;
    } else {
      if (dwRebootRequired & (DI_NEEDREBOOT | DI_NEEDRESTART)) {
        // A reboot is required.
        * RebootRequired = TRUE;
      }
			break;
    }

Public Declare Function InstallSelectedDriver Lib "newdev.dll" _
 (ByVal hWndParent As Long, ByVal DeviceInfoSet As Long, _
 ByVal Reserved As Long, ByVal Backup As Long, ByRef bReboot As Long) As Boolean

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long 'путь не указываем, и dll по дефолту не найдется

'вызов
CPP_MyFunction 

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long 'путь не указываем, и dll по дефолту не найдется

  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = LoadLibrary("PathToDll\cpp_my_dll.dll") 'загрузили, указав путь
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction Lib ") 
    If ProcAdd <> 0 Then
      'вызов
      CPP_MyFunction 'вызов сработал
    End If
    'Делаем  FreeLibrary -все законно, убираем ВСЕ reference, все по MSDN
    Dim FreeResult As Long
    FreeResult = 1
    Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
      FreeResult = FreeLibrary(hMod)
      Debug.Print FreeResult
    Loop
  End If
  'еще вызов
  CPP_MyFunction '< и вот здесь будет crash!!! а не Run-time error '53' 

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long 'путь не указываем, и dll по дефолту не найдется

  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = LoadLibrary("PathToDll\cpp_my_dll.dll") 'загрузили, указав путь
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction Lib ") 
    If ProcAdd <> 0 Then
      'вызов
      CPP_MyFunction 'вызов сработал
    End If
    'Делаем  FreeLibrary -все законно, убираем ВСЕ reference, все по MSDN
    Dim FreeResult As Long
    FreeResult = 1
    Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
      FreeResult = FreeLibrary(hMod)
      Debug.Print FreeResult
    Loop
  End If
  'еще вызов
  CPP_MyFunction '< и вот здесь будет crash!!! а не Run-time error '53' 

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long

  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = LoadLibrary("cpp_my_dll.dll")
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction")
    If ProcAdd <> 0 Then
      '====
      Dim FreeResult As Long
      FreeResult = 1
      Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
        FreeResult = FreeLibrary(hMod)
        Debug.Print FreeResult
      Loop
      '====
      CallWindowProc ProcAdd, 0, 0, 0, 0
    End If
  End If

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long 'путь не указываем

Public Function MyLoad_MyFunction(ByVal PathToDll As String) As String
  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = LoadLibrary(PathToDll)
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction")
    If ProcAdd <> 0 Then
      MyLoad_MyFunction= PtrToString(CPP_MyFunction) 'а не по ProcAdd!!!
    End If
    Dim FreeResult As Long
    FreeResult = 1
    Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
      FreeResult = FreeLibrary(hMod)
      Debug.Print FreeResult
    Loop
  End If
End Function

hMod = GetModuleHandle(PathToDll) 'проверяем загружена ли уже

  If hMod = 0 Then hMod = LoadLibrary(PathToDll) 'загружаем только если не загружена

Public Declare Function CPP_MyFunction Lib "cpp_my_dll.dll" () As Long 'путь не указываем

Public Function My_CPP_MyFunction(ByVal PathToDll As String) As String
  Dim hMod As Long
  Dim ProcAdd As Long
  hMod = GetModuleHandle(PathToDll) 'проверяем загружена ли уже
  If hMod = 0 Then hMod = LoadLibrary(PathToDll) 'загружаем только если не загружена
  If hMod <> 0 Then
    ProcAdd = GetProcAddress(hMod, "CPP_MyFunction")
    If ProcAdd <> 0 Then
      My_CPP_MyFunction= PtrToString(CPP_MyFunction)
    End If
    '!!!А вот этого делать не надо
    'Dim FreeResult As Long
    'FreeResult = 1
    'Do Until FreeResult = 0 ' OK, library reference count is 0, and library is therefore unloadable
    '  FreeResult = FreeLibrary(hMod)
    'Loop
  End If
End Function

...CallWindowProc(ProcAdd, 0, 0, 0, 0))

'Public Declare Function CallWindowProc Lib "user32" Alias "CallWindowProcA" (ByVal lpPrevWndFunc As Long, _
' ByVal hwnd As Long, ByVal Msg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long