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ADODataset in dll and ShareMem

Posted on 2003-02-25
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Last Modified: 2010-04-04
First of all, is it possible to declare function of type TDataSet with stdcall
like
function NotesList(sOwner:string):TDataSet;stdcall;
 If it is, should I include ShareMem in my dll?

Or there is a better way to do this?

What I want to do is to separate data access from the rest of my application, because database might be Access, SQL Server or Firebird. They all have slightly different SQL syntax.
But I still want to get TDataSet or TADODataSet from the data access layer because I want to be able to do further processing with it before binding to a grid.

I know I can do that by writing an additional class that will be in exe, but I am considering dll for some reasons.
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Question by:bogiboy
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mocarts earned 200 total points
ID: 8023792
first of all your function have a string parameter which requires ShareMem if used in dll.
and yes, if you want pass between exe and dll TDataSet (as it uses strings too) then you need include ShareMem as your first unit in project.

wbr, mo.
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by:mocarts
ID: 8023814
one note: you should use ShareMem in both - exe and dll

as far as I know, there is two alternatives to ShareMem (which is wraper for DLL) - FastShareMem and MultiMM (search in Google for keywords). but both have some disantvages and advantages (I don't like disantvages in memory managmen - so when I need to use shared memory I use standard ShareMem)

wbr, mo.
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by:bogiboy
ID: 8027262
Thanks mocarts
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Expert Comment

by:Rusty_Knight
ID: 8033546
I think it must be
function NotesList(sOwner:WideString):TDataSet;stdcall;

and no problem with ShareMem
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Expert Comment

by:mocarts
ID: 8033602
stdcall is calling convention - it don't manage memory.
from delphi help:
"If a DLL exports routines that pass long strings or dynamic arrays as parameters or function results (whether directly or nested in records or objects), then the DLL and its client applications (or DLLs) must all use the ShareMem unit"

TDataSet uses strings (Filter, Name etc.)
wbr, mo.
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Expert Comment

by:Rusty_Knight
ID: 8033703
mocarts, you are right.
But in this case we send WideString and TDataset automaticaly convert it to string.
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Expert Comment

by:mocarts
ID: 8033741
WideString is a parameter
TDataSet is return type..
where is conversion? :)
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