Question

Passing String Arguments VBA / Visual Basic

Asked by: CyberUnDead

What is the proper way to pass string parameters between my host application, which is Access 2003, and my library, which is Visual Basic 6?

I am using the technique outlined in this article http://oreilly.com/pub/a/windows/2005/04/26/create_dll.html or here http://www.vb-helper.com/howto_make_standard_dll.html to create a standard DLL (not ActiveX/COM) using Visual Basic 6.  

My console output from the code below is:
false
false

If I hard code the string parameter as "\\server" inside the DLL it returns true. 

'DLL Library
Public Function IsUNCPath(strPath As String) As Boolean
    On Error GoTo Error_Handle
 
    If Left(strPath, 2) = "\\" Then
        IsUNCPath = True
    Else
        IsUNCPath = False
    End If
 
Exit_Procedure:
    Exit Function
 
Error_Handle:
    Resume Exit_Procedure
End Function
 
 
'Calling Application
Private Declare Function IsUNC Lib "core" Alias _
    "IsUNCPath" (strPath As String) As Boolean
        
Sub TestCoreLibrary()
    Call LoadDLL("core.dll")   'load custom dll
    
    Debug.Print IsUNC("c:\") 'should return false
    Debug.Print IsUNC("\\server1") 'should return true
 
    Call UnloadDLL("core.dll") 'unload custom dll
End Sub

                                  
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Asked On
2009-10-22 at 05:23:03ID24834155
Tags

visual basic

,

vba

,

DLL

Topics

Visual Studio

,

Visual Basic Programming

,

Microsoft Access Database

Participating Experts
2
Points
350
Comments
5

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Answers

 

by: BillDenverPosted on 2009-10-22 at 05:31:33ID: 25633294

Pass the string into the function with double quotes:

IsUNCPath("\\test\XXX\...")

or with anoter function whose output is a string

Public Function xyz() as String
  ...do something that gets string info
End Function

thus
IsUNCPath(xyz())

 

by: egl1044Posted on 2009-10-22 at 05:57:45ID: 25633539

Your decleration should be be passed ByVal you might also need to do the conversion on your side this means converting the string to unicode first.

The same function already exists using API
PathIsUNC Function
http://msdn.microsoft.com/en-us/library/bb773712(VS.85).aspx

Private Declare Function IsUNC Lib "core" Alias "IsUNCPath" (Byval strPath As String) As Boolean

                                              
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by: CyberUnDeadPosted on 2009-10-22 at 06:38:26ID: 31644447

Needed to convert string to unicode before passing to Library.

 

by: CyberUnDeadPosted on 2009-10-22 at 06:53:00ID: 25634156

I needed to convert the string parameter to unicode before passing off to the Library.   A handy conversion function can be found here http://www.experts-exchange.com/Programming/Programming_Languages/Visual_Basic/Q_21063650.html.

I wasn't aware of the API function, which I will implement.   I just happen to pick this function as it is a trivial example to demonstrate my problem.   Included below is the conversion function from the aforementioned link as well as the revised TestCoreLibrary subprocedure.   Now the console reports the values of false, true. 

Function AsciiToUnicode(ByRef pstrAscii)
    On Error GoTo Error_Handle
 
    Dim llngLength
    Dim llngIndex
    Dim llngAscii
    Dim lstrUnicode
 
    llngLength = LenB(pstrAscii)
 
    For llngIndex = 1 To llngLength
        llngAscii = AscB(MidB(pstrAscii, llngIndex, 1))
        lstrUnicode = lstrUnicode & Chr(llngAscii)
    Next
 
    AsciiToUnicode = lstrUnicode
 
Exit_Procedure:
    Exit Function
 
Error_Handle:
    Resume Exit_Procedure
End Function
 
Sub TestCoreLibrary()
    Call LoadDLL("core.dll")
  
    Debug.Print IsUNC(AsciiToUnicode("c:\"))
    Debug.Print IsUNC(AsciiToUnicode("\\server"))
    
    Call UnloadDLL("core.dll")
End Sub
                                              
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by: egl1044Posted on 2009-10-22 at 07:21:20ID: 25634521

You should be able to use a string pointer which will do the conversions for you. If you have a string parameter declare it using (Long) and pass it a string pointer.

Private Declare Function IsUNC Lib "core" Alias "IsUNCPath" (Byval strPathPtr As Long) As Boolean
 
 
'// use it like this.
debug.print IsUNC(strptr("c:\"))
debug.print IsUNC(strptr("\\server1"))

                                              
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