RE: Linking Windows dll with GCC application on cygwin.

["Joseph D. Wagner" <wagnerjd at prodigy dot net>]

LINKING AN EXECUTABLE TO A DLL

An executable file links to (or loads) a DLL in one of two ways: 

*Implicit linking 
*Explicit linking 

Note   Implicit linking is sometimes referred to as static load or load-time
dynamic linking. Explicit linking is sometimes referred to as dynamic load
or run-time dynamic linking.

With implicit linking, the executable using the DLL links to an import
library (.LIB file) provided by the maker of the DLL. The operating system
loads the DLL when the executable using it is loaded. The client executable
calls the DLL's exported functions just as if the functions were contained
within the executable. 

With explicit linking, the executable using the DLL must make function calls
to explicitly load and unload the DLL, and to access the DLL's exported
functions. The client executable must call the exported functions through a
function pointer.

An executable can use the same DLL with either linking method. Furthermore,
these mechanisms are not mutually exclusive, as one executable can
implicitly link to a DLL and another can attach to it explicitly.

LINKING EXPLICITLY

With explicit linking, applications must make a function call to explicitly
load the DLL at run time. To explicitly link to a DLL, an application must: 

*Call LoadLibrary (or a similar function) to load the DLL and obtain a
module handle. 
*Call GetProcAddress to obtain a function pointer to each exported function
that the application wants to call. Because applications are calling the
DLL's functions through a pointer, the compiler does not generate external
references, so there is no need to link with an import library. 
*Call FreeLibrary when done with the DLL. 

For example: 

typedef UINT (CALLBACK* LPFNDLLFUNC1)(DWORD,UINT);
...

HINSTANCE hDLL;               // Handle to DLL
LPFNDLLFUNC1 lpfnDllFunc1;    // Function pointer
DWORD dwParam1;
UINT  uParam2, uReturnVal;

hDLL = LoadLibrary("MyDLL");
if (hDLL != NULL)
{
   lpfnDllFunc1 = (LPFNDLLFUNC1)GetProcAddress(hDLL,
                                           "DLLFunc1");
   if (!lpfnDllFunc1)
   {
      // handle the error
      FreeLibrary(hDLL);       
      return SOME_ERROR_CODE;
   }
   else
   {
      // call the function
      uReturnVal = lpfnDllFunc1(dwParam1, uParam2);
   }
}

-----Original Message-----
From: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org] On
Behalf Of Bansidhar Deshpande
Sent: Saturday, December 07, 2002 9:26 AM
To: gcc-help-help@gcc.gnu.org; gcc-help@gcc.gnu.org
Subject: Linking Windows dll with GCC application on cygwin.

Hi,
I have a dll(dont have source code) written in VC++ 6.0 on Windows NT 
platform. How can I link this dll with the application written in GCC on 
cygwin-1.3.10 .
Regards
Bansidhar





_________________________________________________________________
Protect your PC - get McAfee.com VirusScan Online 
http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963