HOWTO: Implement Array Arguments in Visual C++ COM Objects for Active Server Pages

• Active Server Pages
• Microsoft Visual C++, 32-bit Editions, version 6.0

SUMMARY

This article describes, by example, how to implement arrays to be passed as parameters from Active Server Pages (ASP) to a Visual C++ COM Object.
It is important to keep in mind that array arguments for methods must be declared as variant data type and must the passed by reference. Declaring an array argument any other way may cause an error, such as the following:

error 'ASP 0115' - A trappable error occured in an external object

-or-

Invalid procedure call or argument

-or-

Type Mismatch

-or-

Object Does not Support This property or method

MORE INFORMATION

Use the following steps to implement arrays to be passed as parameters from ASP to a Visual C++ COM Object:

1. Create an ATL DLL Project called ASPArray."



2. Insert an ATL Object named VCArrayObj.


Add a Method with the following information:


Method Name: TestArray<BR/>
Parameters : [in, out] VARIANT* pArray, [out, retval] long* pVal<BR/> 



3. Implement the Method as follows:
   

   
   STDMETHODIMP CVCArrayObj::TestArray(VARIANT *pArray, long *pVal)
   {
       SAFEARRAY *psa;
       long lLBound, lUBound, cElements;  
   	
   if( vArray->vt & VT_BYREF )
       psa = *(vArray->pparray);
   Else
       psa = vArray->parray;
   
       //Check the Dimension of the Array
       if ( SafeArrayGetDim( psa ) != 1 )
       return E_INVALIDARG; 
   
       //Get the lower and upper bounds of the array
       SafeArrayGetLBound( psa, 1, &lLBound );
       SafeArrayGetUBound( psa, 1, &lUBound );
   
       //Compute the Number of Elements
       cElements = lUBound - lLBound + 1;
   
       //Access the elements of the array
       for ( long cCnt = lLBound; cCnt <= lUBound; cCnt++ )
       {
          VARIANT vVal;
          SafeArrayGetElement( psa, &cCnt, &vVal );
       }
   
       *pVal = cElements;    
       return S_OK;
   } 




4. Create an ASP page with the following code:

   
   <%
     Dim oTestObj, vMyArray(2), vRtnValue
              
     vMyArray(0) = "Element 1"
     vMyArray(1) = "Element 2"
     vMyArray(2) = "Element 3"
   
     Set oTestObj = Server.CreateObject("ASPArray.CArrayObj")
     vRtnValue = oTestObj.TestArray( vMyArray )
     Response.Write( "Return Value = " & vRtnValue )
   %> 

Additional query words:

Keywords          : kbASP kbCOMt kbGrpASP 
Version           : winnt:6.0
Platform          : winnt 
Issue type        : kbhowto 

Last Reviewed: May 25, 1999