AsciiZ confusion

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AsciiZ confusion


Sorry this is a long message, but hard to explain.  I have a DLL I wrote in
FreePascal 2.0.2, which is communicating between a Delphi program and a
PowerBasic Dll, like follows...

PBdll exports PBSub ByRef as AsciiZ   <> MyFreePascall_DLL <>

As noted, the Delphi Program integrates a DLL stub which forces me to make
calls using it's pre-defined "Variants Only" format.

The problem comes when I pass data into FPC via "parameters" byRef through a
procedure, into the PowerBasic DLL. The first parameter returns unmodified
and the second parameter returns only one character wide, as if FPC is
trying to receive back a pointer only, to the string space where the PB data
resides.  Or possibly it's just garbage and looks this way.

The FPC DLL is setup as follows:


library DelphiXchg;

uses Variants, strings;

//Declare PowerBasic external (a sub or function call, made no difference)
procedure subXchngAsciiZ(Data1, DATA2:string)stdcall;external 'PB.DLL';

//Declare the Delphi calling stub DLL (variants only);
function Delphstub(var vD1,vD2:variant):variant;stdcall;export;

//at runtime, Delphi sends in... vD1:='test'; vD2:='  '; // (vD2 is
place-held with a 'space')

    if vD1 = 'test'                                    // vD1 is being sent
from Delphi
        then subXchngAsciiZ(vD1, vD2);  // call out to PB DLL
                                                            // vD1 should
come back 'tested'
                                                            // vD2 should
come back 'good'

Delphstub;        // FPC Return value unused


When the Delphi calling program sends in the variant vD1:='test', (through
FPC to the PB DLL), FPC only gets back 'test' unmodified and variant vD2 is
coming back as 'g', (only the first character, instead of 'good', (ahhh but
vD2 did get modified at least)).

I thought that zero or null terminated AsciiZ data would handle the string
array length automatically in FPC, on < 255 wide, but now I'm supposing I
may have to break the variants out, use explicit calls internally by typed
pointer reference and then reload the outgoing variants with the result data
from the pointers to the explicit variables before returning, but I've had
no success in figuring out how to set that up correctly.

Should it really be that much handling to pass AsciiZ on Variant types as
parameters, or am I overlooking something stupid simple?  The only example I
have to go by is a VB program that makes calls directly across to PB, using
ByRef ASCIIZ, so the problem seems mostly from being forced to use the
Variant types in parameters from the Delphi calling program.

Thanks for any ideas.


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