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

  • With JRebel, developers get to see their code changes immediately, fine-tune their code with incremental changes, debug, explore and deploy their code with ease (both locally and remotely), and ultimately spend more time coding instead of waiting for the dreaded application redeploy to finish. Every time a developer tests a code change it takes minutes to build and deploy the application. JRebel keeps the app server running at all times, so testing is instantaneous and interactive.

  • The latest release of SugarCRM's flagship product gives users new tools to build extraordinary customer relationships. Read an in-depth analysis of SugarCRM's enhanced ability to help companies execute their customer-facing initiatives from Ovum, a leading technology research firm.

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds