Solved

Passing a string from a D3 exe to a BCB dll

Posted on 1997-12-26
7
352 Views
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
  • 4
  • 3
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
Industry Leaders: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

 

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 100 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.


0

Featured Post

Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Objective: - This article will help user in how to convert their numeric value become words. How to use 1. You can copy this code in your Unit as function 2. than you can perform your function by type this code The Code   (CODE) The Im…
In my programming career I have only very rarely run into situations where operator overloading would be of any use in my work.  Normally those situations involved math with either overly large numbers (hundreds of thousands of digits or accuracy re…
This video shows how to use Hyena, from SystemTools Software, to bulk import 100 user accounts from an external text file. View in 1080p for best video quality.
Although Jacob Bernoulli (1654-1705) has been credited as the creator of "Binomial Distribution Table", Gottfried Leibniz (1646-1716) did his dissertation on the subject in 1666; Leibniz you may recall is the co-inventor of "Calculus" and beat Isaac…

679 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question