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POUsing C dll in delphi return nothing
 

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    <p>I have been trying to reuse a C dll file in delphi based on this <a href="http://maxdb.sap.com/documentation/sqldbc/SQLDBC_API/SQLDBC__C_8h.html#a252" rel="nofollow noreferrer">documentation</a>. </p> <p>Server was running well, i could access and used the database on local server with java and php.</p> <p>On delphi i used dynamic load and worked well on all functions that return variables but failed on those that return interface.</p> <pre><code>unit for library : unit SQLDBC_C; interface uses windows, classes, sysutils; type SQLDBC_IRuntime = interface end; var getSDKVersion : function :Pchar; stdcall; ClientRuntime_GetClientRuntime: function (errorText:Pchar; errorTextSize:Integer) : SQLDBC_IRuntime; stdcall; implementation var libhandle : THandle; procedure initLibrary; begin libhandle := LoadLibrary('libSQLDBC_C.dll'); if libhandle&gt;=23 then begin @getSDKVersion:=GetProcAddress(libhandle,'getSDKVersion'); @ClientRuntime_GetClientRuntime:= GetProcAddress(libhandle,'ClientRuntime_GetClientRuntime'); end; end; initialization begin initLibrary; end; finalization begin if libhandle&gt;=32 then FreeLibrary(libhandle); end; end. </code></pre> <p>here is the test procedure :</p> <pre><code>procedure TForm1.Button1Click(Sender: TObject); var err : array [0..200] of char; rt : SQLDBC_IRuntime; begin Memo1.Clear; FillChar(err, sizeof(err), 0); Memo1.Lines.Add(getSDKVersion); //this function successed rt := ClientRuntime_GetClientRuntime(@err,200); //this function had no return value, (rt always nil) but no error return at err variable if assigned(rt) then begin ...... end; end; </code></pre> <p>I've read the similar problems asked by <a href="https://stackoverflow.com/questions/2266417/delphi-calling-a-function-from-a-vc-dll-that-exports-a-interface-class">geskill</a>, <a href="https://stackoverflow.com/questions/6629852/delphi-interface-from-dll">Dan Hacker</a>, <a href="https://stackoverflow.com/questions/8846545/is-it-safe-to-use-interfaces-from-dll">max</a> and <a href="https://stackoverflow.com/questions/4798283/calling-dlls-with-pointers-in-delphi">Ron</a> but it could not solve my problem.</p> <p>Could anyone told me what's wrong here?</p>
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    1. COWhich version of Delphi? Are you sure it's stdcall? Quite plausible that it's cdecl.
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      1. USDavid Heffernan
    2. COThis reminds me of this question: http://stackoverflow.com/questions/9349530/why-can-a-widestring-not-be-used-as-a-function-return-value-for-interop
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      1. USDavid Heffernan
    3. CO@DavidHeffernan thanks for reply. There's no differences between stdcall and cdecl. I'm on Windows XP machine, trying Delphi 6, 7 and XE2.
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