Re: Calling ActiveX DLL from MFC - passing arrays

[mla154]

Hello, I have created a function in an ActiveX DLL similar to the function below:

Public Function f1(ByRef arr1() As String, ByRef arr2() As Double) As String()
End Function

How do I create a SAFEARRAY in Visual C++ to successfully pass both of these arrays?

Regards, Mike

[CPallini]

If you put SafeArray into CP article search engine, then a bit of magic happens http://www.codeproject.com/info/search.aspx?artkw=SafeArray&sbo=kw[^] :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[mla154]

The data has been put into the SafeArray. However, when reading the data into the VB ActiveX DLL function, I wrote code to display the contents of the array:

Public Function f1(ByRef arr1() As String, ByRef arr2() As Double) As String()
   ShowList arr1
End Function

Private Sub ShowList(ByRef arr() As String)
    for i1 = LBound(arr, 1) to UBound(arr, 1)
       MsgBox arr(i1)
    next i1
End Sub

The program crashes.

Regards, Mike

[CPallini]

That probably means that SafeArray initialization was wrong on the C++ (client) side. How do you perform that task? :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
[my articles]

[mla154]

SAFEARRAY* CreateASafeArray()
{
//http://www.geocities.com/Jeff\_Louie/safearray.html
USES_CONVERSION; // enables use of ATL conversion macro A2W
char buffer[20]; // used to store ANSI string
HRESULT hr= S_OK;

// Create SafeArray of VARIANT BSTRs
SAFEARRAY \*pSA;
SAFEARRAYBOUND aDim\[1\];    // a one dimensional array
aDim\[0\].lLbound= 0;  // Visual Basic arrays start with index 0
aDim\[0\].cElements= 10;
pSA= SafeArrayCreate(VT\_VARIANT,1,aDim);  // create a 1D SafeArray of VARIANTS
if (pSA != NULL) {
	long aLong\[1\];
	// iterate over array adding VARIANTs of type VT\_BSTR
	for (long l= aDim\[0\].lLbound; l< (long)(aDim\[0\].cElements + aDim\[0\].lLbound); l++) { 
		VARIANT vOut;
		VariantInit(&vOut);
		vOut.vt= VT\_BSTR;  // set type
		\_ltoa\_s(l,buffer,10);  // convert long to ANSI string value
		vOut.bstrVal= ::SysAllocString(A2W(buffer)); // system wide "new"
		aLong\[0\]= l;  // set index value
		if (hr= SafeArrayPutElement(pSA, aLong, &vOut)) { // "correctly" copies VARIANT
			VariantClear(&vOut);  // release BSTR from memory on error
			SafeArrayDestroy(pSA); // does a deep destroy on error
			return NULL;
		}
		VariantClear(&vOut);  // does a deep destroy of source VARIANT
	} // end iteration
}
return pSA;
// clean up here only if you do not return SafeArray as an \[out, retval\]
SafeArrayDestroy(pSA); // again does a deep destroy

}

void CaxDlg::OnBnClickedButton1()
{
SAFEARRAY *pSA3 = CreateASafeArray ();
}

Regards, Mike

[Lim Bio Liong]

Hello Michael, Your VB object method f1 declared arr1() as of type "string". Your CreateASafeArray() C++ function declared the SAFERRAY as holding elements of type VT_VARIANT. This is the problem : VT_VARIANT type is not a string. VT_BSTR is. To resolve the problem, either : 1. Change the signature of f1 to : Public Function f1(ByRef arr1() As Variant, ByRef arr2() As Double) As String() ShowList arr1 End Function or 2. Change the call to CreateSafeArray() in CreateASafeArray() function to : pSA= SafeArrayCreate(VT_BSTR,1,aDim); // create a 1D SafeArray of VARIANTS and then make the appropriate changes to the rest of the code in CreateASafeArray(). Hope the above suggestions will help you. Best Regards, Bio.

[mla154]

Bio., Your second piece of advice allowed the string array to be read correctly.  Thank you.

Regards, Mike

modified on Thursday, January 10, 2008 11:52:12 AM

[Lim Bio Liong]

Congratulations, Michael. Best wishes to your project. - Bio.