Calling GExperts Grep (or an entry point in any Delphi dll) via rundll32.exe

Delphi, GExperts 2 Minutes

GExperts so far comes with a special stand alone executable GExpertsGrep that does nothing else but load the GExperts dll and call the entry point ShowGrep. Having this additional executable isn’t really necessary because Windows already comes with a tool that does exactly that: Load a DLL and call an entry point: rundll32.exe

rundll32 path\to\your.dll,EntryPoint additional parameters go here

In order for a dll to be called in this manner it needs to export an entry point with the following definition:

procedure EntryPoint(_HWnd: HWND; _HInstance: HINST; _CmdLine: PAnsiChar; CmdShow: integer); stdcall;

Note that the calling convention must be stdcall otherwise bad things happen.

Since Windows NT (so for all modern versions of Windows) there are two additional ways to declare the entry point:

procedure EntryPointA(_HWnd: HWND; _HInstance: HINST; _CmdLine: PAnsiChar; CmdShow: integer); stdcall;
procedure EntryPointW(_HWnd: HWND; _HInstance: HINST; _CmdLine: PWideChar; CmdShow: integer); stdcall;

Note that EntryPoint and EntryPointA are still assumed to have a PAnsiChar parameter, while EntryPointW is assumed to have a PWideChar parameter. A Dll only needs to export one of these entry points.

If RunDll32 is called with “EntryPoint”, it will look for “EntryPointW” first, “EntryPointA” second and “EntryPoint” last. Note that you don’t have to specify the “A” or “W” suffix, it is automatically added by RunDll32.

For a change, we even have an advantage when writing the DLL in Delphi rather than in MS Visual C++: Delphi does not do any name mangling, so the entry point will be called exactly what you write in the source code.

So, assuming the GExperts DLL exports the following procedure:

procedure ShowGrepEx(_HWnd: HWND; _HInstance: HINST; _CmdLine: PAnsiChar; CmdShow: integer); stdcall;

RunDll32 could be called like this:

rundll32 path\to\GExperts.dll,ShowGrepEx Some\Directory\here

The DLL would take the _CmdLine parameter, use it as the base directory for a directory search and show you the dialog as above. Pretty cool, eh?

We could even go a step further and write the following to the registry to add an entry to the context menu of each folder in Windows Explorer.

Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\Folder\shell\GExpertsGrep]
"Icon"="path\\to\\GExperts.dll"
"MUIVerb"="GExperts Grep"

[HKEY_CLASSES_ROOT\Folder\shell\GExpertsGrep\Command]
@="\"c:\\windows\\system32\\rundll32.exe\" path\\to\\GExperts.dll,ShowGrepEx %1"

(Note: Don’t just copy that to a .reg file! You need to replace both instances of “path\\to\\GExperts.dll” with the actual absolute path to your GExperts DLL. And don’t forget that the current release does not even export the entry point ShowGrepEx at all.)

And this is what you’d get:

Unfortunately there is a drawback: RunDll32 must be given the correct path and file name of the DLL to load. That’s fine if you only have one GExperts version installed. The current GExpertsGrep stand alone executable searches for the first GExperts DLL in descending order, so it will always load the one for the latest Delphi version it can find. So I am not sure whether I want to drop the stand alone executable in favor of RunDLL32 right now.

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