Using a Multidimensional SAFEARRAY to pass data across from COM objects

The SAFEARRAY is a standard way to pass arrays or collections between COM objects.
Using COM's standard marshaller , we can pass a collection of OLE Automation compatible data types using SAFEARRAYs.
Multidimensional SAFARRAYs help us pass various automation compatible data types through the same array

Assume , we own an icecream parlor and would like to give our customers a list of all the icecream flavors and their prices.
Now wouldn't it be nice to package an array with both the flavor (represented by a BSTR) and the price (represented as a float data type).
Notice that we have two diferent data types one a float and another a BSTR and yet we package them neatly in a SAFEARRAY and send them across using COM's standard marshaller.

Our data structure should look something like this:

		
	 flavor 1     flavor 2		    flavor n	
Flavors  (0,0)        (0,1)   ..........     (0,n) 
		
	  price 1      price 2		    price n
Prices    (1,0)        (1,0)  ..........     (1,n)




You can extend this whole analogy to actually pack every record in a database table into an N-dimensional SAFEARRAY where N represents the number of fields in the table.
While wading through some of the SAFEARRAY documentation , you may happen to come across the term array descriptor. An array descriptor is actually a pointer to an allocated SAFEARRAY structure.

Time now to have a look at our Icecream parlor example.


//////////////////////////////////////////////////////////////////////////////
//Function : GetFlavorsWithPrices (Example for Multidimensional SAFEARRAY)
//Parameters: VARIANT (out parameter that contains a SAFEARRAY of VARIANTs
//			   helping us to pass BSTR and float in the same array)
//Return Type : HRESULT
//////////////////////////////////////////////////////////////////////////////


STDMETHODIMP CIceCreamOrder::GetFlavorsWithPrices(VARIANT *pVariant)
{
	// TODO: Add your implementation code here
	
	
	
	//Initialize the bounds for the array
	//Ours is a 2 dimensional array
	SAFEARRAYBOUND safeBound[2]; 
	
	//Set up the bounds for the first index
	//That's the number of flavors that we have
	safeBound[0].cElements = m_vecIcecreamFlavors.size();    
	safeBound[0].lLbound = 0;

	//Set up the bounds for the second index
	safeBound[1].cElements = m_vecIcecreamPrices.size();
	safeBound[1].lLbound = 0 ;

	
	///Initialize the VARIANT
	VariantInit(pVariant);
	//The array type is VARIANT
	//Storage will accomodate a BSTR and a float
	pVariant->vt = VT_VARIANT | VT_ARRAY; 
	pVariant->parray = SafeArrayCreate(VT_VARIANT,2,safeBound);
	
	
	//Initialize the vector iterators
	std::vector::iterator iterFlavor;
	std::vector<float>::iterator iterPrices;


	
	//Used for indicating indexes in the Multidimensional array
	long lDimension[2];
	int iFlavorIndex = 0;

	
	//Start iteration
	iterPrices = m_vecIcecreamPrices.begin();
	iterFlavor = m_vecIcecreamFlavors.begin(); 


	//Iterate thru the list of flavors and prices
	while(iterFlavor != m_vecIcecreamFlavors.end()) 
	{

		
		//Put the Element at (0,0), (0,1)  , (0,2) ,.............(0,n)
		lDimension[1] = iFlavorIndex;
		lDimension[0] = 0;
		CComVariant variantFlavor(SysAllocString((*iterFlavor).m_str));
		SafeArrayPutElement(pVariant->parray,lDimension,&variantFlavor);

	
		
		//Put the Element at (1,0), (1,1)  , (1,2) ,.............(1,n)
		lDimension[1] = iFlavorIndex;
		lDimension[0] = 1;
		CComVariant variantPrices(*iterPrices);
		SafeArrayPutElement(pVariant->parray,lDimension,&variantPrices);
	
		
		iFlavorIndex++;
		iterPrices++;
		iterFlavor++;
		

	}
	
	return S_OK;

}


Download demo project (Server) - 32 KB

Download demo project (Client) - 18 KB



Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • The explosion in mobile devices and applications has generated a great deal of interest in APIs. Today's businesses are under increased pressure to make it easy to build apps, supply tools to help developers work more quickly, and deploy operational analytics so they can track users, developers, application performance, and more. Apigee Edge provides comprehensive API delivery tools and both operational and business-level analytics in an integrated platform. It is available as on-premise software or through …

  • Live Event Date: September 10, 2014 @ 11:00 a.m. ET / 8:00 a.m. PT Modern mobile applications connect systems-of-engagement (mobile apps) with systems-of-record (traditional IT) to deliver new and innovative business value. But the lifecycle for development of mobile apps is also new and different. Emerging trends in mobile development call for faster delivery of incremental features, coupled with feedback from the users of the app "in the wild". This loop of continuous delivery and continuous feedback is …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds