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C++ DLL> Parameters from VB

Posted on 1998-12-31
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Last Modified: 2010-04-02
Hi,

I try to call a function in a DLL from VB, and I have few problems:

VB Declaration>
Public Declare Function GetDocumentPathname Lib "ps_API10.dll" (ByVal sString1 As String, ByRef sString2 As String) As Long
VB Code>
Response = GetDocumentPathname("Some text", sDocPathname)

C++>
long __stdcall CWordAPIApp::GetDocumentPathname(char sString1[100],char* sString2)
{
     strcpy(sString2, sString1);
     Return (0);
}

I'm expecting in my VB code to get: sDocPathName = "Some text", but it doesn't work.
I guess there is a problem with passing parameter by value or by reference, but I cannot find which (can I use 'strcpy' for this kind of job? ).

Any idea?

Thanx
0
Comment
Question by:SergeD
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9 Comments
 
LVL 13

Expert Comment

by:Mirkwood
ID: 1181335
Both parameters should be byval
0
 

Author Comment

by:SergeD
ID: 1181336
What do you mean, byval?

I'd like to pass one by value and one by reference. So I can assign one with the other.

Isn't it possible?
0
 
LVL 13

Expert Comment

by:Mirkwood
ID: 1181337
string by reference is char** in C++
string by value is char*

0
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Author Comment

by:SergeD
ID: 1181338
So, the right C++ declaration should be:
long __stdcall CWordAPIApp::GetDocumentPathname(char* sString1,char** sString2)

but how to use strcpy?
 
strcpy(*sString2, sString1); ?
 
Ta,
0
 

Expert Comment

by:Mithander
ID: 1181339
I belive you want something like this.  Assuming the VB is right, the C++ should be.

long __stdcall CWordAPIApp::GetDocumentPathname(char* sString1,char** sString2)
{
char *temp=new char[strlen(sString1)+1];
strcpy(temp,sString1);
delete (*sString2);
(*sString2)=temp;
}

the only problem might be with the new and delete.  I was told you need to use them, but I'm not sure if this is the right way.  I don't think that you can just copy over the string, because you don't know the size of the block of memory it stores.
0
 

Author Comment

by:SergeD
ID: 1181340
So, the right C++ declaration should be:
long __stdcall CWordAPIApp::GetDocumentPathname(char* sString1,char** sString2)

but how to use strcpy?
 
strcpy(*sString2, sString1); ?
 
Ta,
0
 

Author Comment

by:SergeD
ID: 1181341
Hi Lads!

Thanx for your answers, much appreciated.

I give the points to Mithander, but another question is waiting for Mirkwood.

Bye.
Serge
0
 

Accepted Solution

by:
Mithander earned 60 total points
ID: 1181342
Thanks Serge
0
 
LVL 10

Expert Comment

by:viktornet
ID: 1181343
SergeD, your function isn't working in VB because VB doesn't use zero (NULL) based strings,  declares the strings in its own way...

-Viktor
--Ivanov
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