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Passing a string from a D3 exe to a BCB dll

Posted on 1997-12-26
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Last Modified: 2010-05-18
I am trying to pass a string as an argument from a D3 exe to a BCB dll. The BCB docs indicate that if one uses a char pointer, it is not required to use bcbmm.dll. A doc at the Borland website, "Extending Delphi with DLLs" provides snippets illustrating how this is done. Unfortunately I can not get this to work.

BCB code:

extern "C" __pascal __declspec(dllexport) int AddVals(int nA, int nB, int nC, int nD)
{
      return (nA+nB+nC+nD);
}

/*
This is from "Extending Delphi with DLLs" found at the Borland website
*/

int far _export pascal PassCharPtr(char far* strA)
{
      MessageBox(NULL, strA, "GPC_TPL", MB_OK);
      return (strlen(strA));
}

D3 code:
  function ADDVALS(nA,nB,nC,nD: integer):integer; stdcall; far external 'GPC_TPL.DLL' index 2;
  function PASSCHARPTR(strParam: PChar):integer; external 'GPC_TPL' index 1;


var
  Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.Button1Click(Sender: TObject);
const
  StringLength = 255;
var
  nRetVal: integer;
  strA: array[0..StringLength] of char;
begin
  nRetVal := ADDVALS(1,2,3,4);
  ShowMessage(IntToStr(nRetVal));

  StrPCopy(strA, 'Hello World!');
  nRetVal := PASSCHARPTR(strA);
  ShowMessage(IntToStr(nRetVal));
end;

The PassCharPtr method in the dll does not receive the string as a argument and returns the length of the string as 3 no matter what the string length really is.

BCB suggests adding bcbmm.lib to both the dll and exe. I cannot seem to add bcbmm.lib to the D3 exe.

When I add ShareMem.pas to the dll project and put ShareMem at the head of my uses list, I get the same results plus when I close the exe an InvalidPointer exception is thrown.

Suggestions on how to successfully pass a string (<255 char) as an argument from a D3 exe to a BCB dll method will be greatly appreciated.

thanks
A.G.
0
Comment
Question by:AG112297
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7 Comments
 
LVL 3

Expert Comment

by:altena
ID: 1354626
I remember having had a small fight with D2 just like you have
here.

Try this (and reject the answer if it does not work, I do not
remember exactly whenand why I had to pull this stunt)

replace:
nRetVal := PASSCHARPTR(strA);

with
nRetVal := PASSCHARPTR(&strA[0]);

and if it does work, well an "A" would be nice ;-)
0
 

Author Comment

by:AG112297
ID: 1354627
Unfortunately Delphi 3 informs me that the ampersand is an "illegal character in input file" and as such will not compile. Thank you for the effort.
0
 
LVL 3

Expert Comment

by:altena
ID: 1354628
Ok, so i use C++ now...

try again with the "@" character.

// If that also does not compile, I will actually fire up
// delphi and re-invent the "address off" operator :-)
0
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Author Comment

by:AG112297
ID: 1354629
The D3 compiles but when it executes and invokes the dll's PassCharPtr method, the results are unchanged. I have been trying to find more information on the calling convention as I think that is where the problem might lie. FWIW both methods work fine when invoked from a BCB exe.

Thanks again.
0
 
LVL 3

Expert Comment

by:altena
ID: 1354630
hmmm, I'll give this one last (this will be my last "answer") try:

Take another look at the Delphi declarations:
--
D3 code:
function ADDVALS(nA,nB,nC,nD: integer):integer; stdcall; far external 'GPC_TPL.DLL' index 2;
function PASSCHARPTR(strParam: PChar):integer; external 'GPC_TPL' index 1;
--
The second function, the one with the pchar, does NOT have a
"stdcall" keyword.

 Happy new year. (even if this also does not help)
0
 
LVL 3

Accepted Solution

by:
altena earned 300 total points
ID: 1354631
hmmm, I'll give this one last (this will be my last "answer") try:

Take another look at the Delphi declarations:
--
D3 code:
function ADDVALS(nA,nB,nC,nD: integer):integer; stdcall; far external 'GPC_TPL.DLL' index 2;
function PASSCHARPTR(strParam: PChar):integer; external 'GPC_TPL' index 1;
--
The second function, the one with the pchar, does NOT have a
"stdcall" keyword.

 Happy new year. (even if this also does not help)
0
 

Author Comment

by:AG112297
ID: 1354632
I figured that out this afternoon. I next ran into a problem when I 'combined' the two methods into one, DoItAll(char*,int,int,int,int). Using the calling conventions above, the method wouldn't work. I finally tried the basic convention,
int __export DoItAll(LPTSTR strA, int nA, int nB, int nC, int nD)
and it worked. The name is mangled but since I will call the method ordinally from D3 it doesn't matter to me. Thanks for the help.


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