Delphi – How to call a Delphi DLL from VB6

declaredelphidllvb6

Given the following Delphil DLL declaration

function csd_HandleData(aBuf: PChar; aLen: integer): integer; stdcall;

what would be the VB6 declaration to use it?

I've tried a variety of declarations, e.g.

Declare Function csd_HandleData Lib "chsdet.dll" (ByVal aBuf As String, ByVal aLen As Integer)
Declare Function csd_HandleData Lib "chsdet.dll" (aBuf As Long, ByVal aLen As Integer)
Declare Function csd_HandleData Lib "chsdet.dll" (aBuf As Byte, ByVal aLen As Integer)

with the relevant code to suit the parameters, but nothing seems to work, i.e. the Delphi debugger says I have a too-largish value in aLen and a null string in aBuf.

I am working toward using a TypeLib to drive the connection, but was prototyping with Declares.

Best Answer

try

Declare Function csd_HandleData Lib "chsdet.dll" (ByVal aBuf As String, 
ByVal aLen As Integer) As Integer

Seems you forgot the return value.

Related Solutions

Delphi – Testing Delphi DLL crashes VB6 IDE

To elaborate on GSerg's answer:

result := PWideString(s);

you'd think it would be ok because s was initialized with a string literal... but wide strings in Delphi are not reference counted like normal strings, so s actually holds a bit of dynamically allocated heap memory, and as soon as the function returns this memory can be reused :(

The following should be ok though:

function foo() : PWideString;
const s : WideString = 'My dog''s got fleas';
begin
  result := PWideString(s);
end;

Delphi – Get string return value from C DLL in Delphi

Consider rewriting your test code as follows:

var
  p1, p2 : pchar;
begin
  GetMem( p1, 255 ); // initialize
  GetMem( p2, 255 );
  StrPLCopy( p2, 'some string to decrypt', 255 ); // prevent buffer overrun
  StrPLCopy( p1, DecryptStr( p2 ), 255); // make a copy since dll will free its internal buffer
end;

If still fails within a call to DecryptStr, then read http://support.microsoft.com/kb/187912 carefully.

Best Answer

Related Solutions

Delphi – Testing Delphi DLL crashes VB6 IDE

Delphi – Get string return value from C DLL in Delphi

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