Calling an Exported Function in an EXE from Within a DLL

Environment: VC6, SP4, 2K, SP2

This article explains a better way of calling a function in an EXE file from a dependent DLL of the same EXE. In other words, calling a DLL's function from an EXE is the normal way; this is the reverse of the same.

On CodeGuru I have found a couple of FAQs talking about the same issue. They tell you to have a call back function to hold the pointer from the EXE and so on, but they look primitive. In this article, I have given a better method of calling functions from the EXE. I would be glad if this helps someone in need.

In the EXE:

// Do exactly as you would export a DLL...
extern "C"
{
  EXPORT void ExeFn(char * lpszMessage)
  {
    MessageBox(NULL,lpszMessage,"From Exe",MB_OK);
  }
}

In the DLL:

        ...
// Get the handle of the EXE that loaded us.

FnPtrT FnPtr = (FnPtrT)::GetProcAddress(GetModuleHandle(NULL),
                "ExeFn");
if(FnPtr)
  (*FnPtr)("Message From The DLL");
else
  MessageBox(NULL,"It Did Not work :(","From DLL",MB_OK);

        ...

Downloads

Note: In this demo project, I have just implemented the above-mentioned exports. The EXE calls the DLL's function and that function calls a function in the EXE. Those functions do nothing more than display message boxes, so there's no point in giving a demo EXE. Just build the source; you must get the DLL and EXE.

How to Build It

  • Extract the source zip file. Open workspace "ExportingExe.dsw".
  • Ensure that ExportingExe is the active project. Now, you can build and run it.
  • Because Importing.DLL is a dependency of the other one, you don't have to bother about anything else.
Download source - 16 Kb


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