ShareMem/ string-exchanging with Delphi DLL

Question

Quick one I hope - I'm just about to delve into a Delphi 5 legacy app that makes calls to a DLL (also written in D5), passing a string which the DLL can modify if required.

I have the code to both the DLL and the app. Pasted right at the top of the DLL source is a remark about using ShareMem, and it needing to be the first line in the uses clause of the project etc.

If I was porting this whole thing to D2007, is there a better (or more modern) way of getting a Delphi app to share string data with a Delphi DLL? Does the D5 ShareMem stuff still apply to Delphi 2007 applications (with FastMM etc)? I haven't even had a bash at recompiling the whole thing yet - just wondered if this bit was going to be a problem and if there was an alternative/recommended way of doing this?

FWIW, the DLL is totally first party (it's only used by this particular app - so recompiling it under D2007 as well wouldn't be a problem).

Answer 1

To use the FastMM included with D2007, use SimpleShareMem as the 1st unit in both your application and the DLL projects.

Or download the full FastMM4 from SourceForge, set the Flags in FastMM4Options.Inc (ShareMM, ShareMMIfLibrary, AttemptToUseSharedMM) and put FastMM4 as the 1st unit in both the application and the DLL projects.

Answer 2

The reason you need sharemem is that the reference counting on ansistrings breaks when passed to a dll. One solution is :-

If you are able to restrict your strings to shortstring then you can dispense with sharemem. I have written some two dozen dlls, mostly drivers for hardware and I have not had to use sharemem once.

Answer 3

Use only a FastMM4. FastMM4 is a great memory manager and automatically includes a ShareMem like solution! FastMM4 is compatible with D5 and up!