return String of PBDLL 6.0 to VB6.0

[amauri siqueira]

I work with VB using dll of PBDLL 6.0
I have had some problems because,

I declare this way in VB 6.0

Public Declare Function CompactaNumero Lib "TACO.DLL" Alias "COMPACTANUMERO" (ByVal Amimi As String) As String


The function in Power Basic DLL 6.0
FUNCTION CompactaNumero ALIAS "COMPACTANUMERO" (BYVAL Amimi AS STRING) EXPORT AS STRING
LOCAL largo AS INTEGER
LOCAL vitima AS STRING
LOCAL retorno AS STRING
LOCAL intermedio AS DOUBLE
LOCAL RecibeMIMI AS STRING
DIALOG DOEVENTS
RecibeMIMI = Amimi
retorno= mid$(Amimi ,1,2)
DIALOG DOEVENTS
CompactaNumero = retorno

END FUNCTION

it sometimes returns me a correct value and other times it returns me incoherences.

please help me


Amauri

------------------

[Fred Oxenby]

You should declare this way in VB 6.0

Public Declare Function CompactaNumero Lib "TACO.DLL" Alias "COMPACTANUMERO" (ByRef Amimi As String) As String 

This is the correct way to interpret the PB-function

Function CompactaNumero(Byval Amimi As String)Export as String
 ....
End Function

But what are your Dialog Doevents doing in your DLL-function?

------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se



[This message has been edited by Fred Oxenby (edited January 24, 2001).]

[amauri siqueira]

dear i change a sholder in vb , but d'ont make correct.

I use DIALOG DOEVENTS for result but d'ont result.


Please help me

Amauri

------------------

[Tom Hanlin]

VB does funny things with strings. If you specify BYVAL with a VB string,
you should use ASCIIZ on the PowerBASIC side. If you don't use BYVAL with
a VB string, you should use STRING on the PowerBASIC side.

' If you have this in VB...
Declare Sub Foo Lib "taco.dll" Alias "FOO" (Whatever As String)
' Use this in PowerBASIC:
Declare Sub Foo (Whatever As STRING) Export

' If you have this in VB...
Declare Sub Foo Lib "taco.dll" Alias "FOO" (BYVAL Whatever As String)
' Use this in PowerBASIC:
Declare Sub Foo (Whatever As ASCIIZ) Export

------------------
Tom Hanlin
PowerBASIC Staff

[Fred Oxenby]

Tom, No offence but
When I wrote my answer, I was afraid of your discussion.
I think it is a little bit confusing.
Perhaps, and only perhaps it is possible for Mr Siqueira to change the DLL
In normal case, you have a 'readyToUse function in the DLL, and have to find
the best declaration for it.
---
My understanding of 'Byval String' in Powerbasic is that when called from Powerbasic,
the compiler creates a copy of the string and send this 'Byref String'
in other words, 'Byval String' and 'Byref String' both expect a pointer to
a string description, not string data.
---
I would very much appreciate your comment/correction





------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

[Lance Edmonds]

the "problem" is not with powerbasic, but with the way vb handles the byval and byref keywords differently when passing dynamic strings to dll's.

when vb passes a byref string to a dll, vb passes a pointer to an (ansi) ole string handle to powerbasic. powerbasic can directly use this ole string handle pointer (since that is what pb uses internally for dynamic strings), so the powerbasic code will need to be expecting to receive a byref string.

however, when vb passes the string byval to a dll, it converts the string from unicode to ansi and formats it as asciiz string, and passes a pointer to the string data to the dll. therefore, the powerbasic code must be written to accept a byref asciiz string.

for more information, please consult the appendix on vb in the pb/dll helpfile, and the vb strings faq in the faq forum at http://www.powerbasic.com/support/pb...hread.php?t=26

i hope this helps!


------------------
lance
powerbasic support
mailto:[email protected][email protected]</a>

[Fred Oxenby]

Lance, if your answer was aimed at my question, you surely succeded in avoiding
the question.

The Question is simple:
In a PB DLL There is a function like this
Function GetString(Byval String)Export as String
This function expects an (ANSI) OLE string handle (your word)
Called from Powerbasic code the compiler vill recognize the Byval keyword
and make a copy of the string and supply OLE string handle to the copy
------
If I want to use this function from VB I have to declare it in a way that the VB-compiler
correctly set up the call.
To get VB to supply OLE string handle you use "BYREF STRING" in VB-declaration
-----
Later, if you want (in VB) to mimic the handling of Powerbasic "BYVAL STRING"
you explicit instruct VB to use a copy of the string when calling the PB/DLL function
----
MyString$ = GetString((orginalString$))


------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se

[Tom Hanlin]

If it's declared BYVAL..AS STRING on the PB/DLL side, use BYREF..AS STRING
on the Visual Basic side.

There's no need for GetString at all, as far as I know.

------------------
Tom Hanlin
PowerBASIC Staff

[Fred Oxenby]

Tom, GetString was a function in a PB/DLL
It was silly of me to use that function-name.
Think of it as;
Function AnyFunction(Byval x as string)Export as String
-------
Thanks anyway for your answer.That was the answer I hoped for..

------------------
Fred
mailto:[email protected][email protected]</A>
http://www.oxenby.se