Re: DLL declarations created by VC++ app wizard
You are asking me to 'Load the DLL imlicitly'. I have tried it and works
fine. For that I don't have to do any changes to what the App Wizard had
created.
I want to test loading it explicitly / dynamically as eventually I will be
using it with a VB6 program. If I want to load it explicitly, then I
shouldn't link with the .lib. The sequence of operations as per the help doc
is:
1. Call LoadLibrary and get the handle - I get it, no problem.
2. Call GetProcAddress to get the pointer to the external function. - I
realized this after posting the original problem. I do fial on this. The
call is not succeeding.
3. Call the external function - This fails in linking itself, as the errors
that I presented.
4. Call FreeLibrary after finishing with it - I get it, no problem.
I have gone through "DLLs in Win32" on MSDN / VS Help. It talks of a sample
program "PortTool". It talks about defining a Function Table, a .DEF file.
The sample program doesn't have any call to LoadLibrary or FreeLibrary. I
didn't find any .DEF file for it. I tried using the Function Table as
described here, but in vain. Even the DLLTRACE is not following what is
preached in these docs. I think, they all doing a Implicit Linking to the
dll.
ThanQ...
"Norbert Unterberg" <nunterberg@newsgroups.nospam> wrote in message
news:%234RSycQPIHA.5184@TK2MSFTNGP05.phx.gbl...
SME schrieb:
Hi,
I have created a dll project using app wizard. It created the
dll_w32_export.h file as below:
----------------------------------------------
#ifdef DLL_W32_EXPORT_EXPORTS
#define DLL_W32_EXPORT_API __declspec(dllexport)
#else
#define DLL_W32_EXPORT_API __declspec(dllimport)
#endif
// This class is exported from the dll_w32_export.dll
class DLL_W32_EXPORT_API CDll_w32_export {
public:
CDll_w32_export(void);
// TODO: add your methods here.
};
extern DLL_W32_EXPORT_API int nDll_w32_export;
DLL_W32_EXPORT_API int fnDll_w32_export(void);
------------------------
My app code segement is:
int ret;
int OldErrMode;
HANDLE hDll;
// load dll
// set err mode to let app handle critical errors
OldErrMode = SetErrorMode (SEM_FAILCRITICALERRORS);
hDll = LoadLibrary ("dll_w32_export.dll");
SetErrorMode (OldErrMode);
if (!hDll)
{
ErrorNotify (IDS_LOADLIBFAILED);
return 1;
}
ret = fnDll_w32_export();
-------------------------------------
First I got link error:
error LNK2001: unresolved external symbol "__declspec(dllimport) int
__cdecl fnDll_w32_export(void)" (__imp_?fnDll_w32_export@@YAHXZ)
Then I added #define DLL_W32_EXPORT_EXPORTS
Now I get the error:
error LNK2001: unresolved external symbol "int __cdecl
fnDll_w32_export(void)" (?fnDll_w32_export@@YAHXZ)
What am I missing?
You are missing several things:
You need to #define DLL_W32_EXPORT_EXPORTS in your DLL project (when
creating the DLL), not in your application project. This makes the linker
export the class and the public symbols. It means that the classes
functions and the publich functions and variables are put into the DLL's
export table and to the import library file.
In your application, include the dll_w32_export.h without defining the
DLL_W32_EXPORT_EXPORTS.
Link the application against the dll_w32_export.lib file which is created
when linking the DLL. It is the DLL's import library that the linker
generates when linking the DLL.
Believe me, you do not want to dynamically load the DLL at runtime with
LoadLibrary. By linking the application against the DLL's import library
you tell windows to autimatically load the DLL when the application is
started.
Norbert