Question

I have MSXML2::IXMLDOMNodeList interface.
I can find the common length of all MSXML2::IXMLDOMNode-s from this list using such code:

MSXML2::IXMLDOMNode* pDOMXMLNode = 0;
BSTR NodeText;
ULONG lValueSize = 0;
ULONG lCommonLength = 0;
while(pDOMXmlNodeList->nextNode(&pDOMXMLNode)== S_OK)
{      
 pDOMXMLNode->get_xml(&NodeText);      
 CString strNode(NodeText);
 lValueSize += strNode.GetLength();      
}    
lCommonLength += lValueSize;

It is good, but it is not what i want to find: i want to determine object instance’s size in memory.
Is there a way to make it in C++?

Answer 1

I’m not sure if you can determine exact size of COM object. However, you can use the following trick to determine approximate size of COM objects.

//First determine how much memory your program is currently using. 
//Say it is currently `m1`

//allocate COM object

//Now again, determine how much memory your program is using
//Say it is m2

//COM object size = m2 - m1

Microsoft provides some API to determine the memory state of the program. Here is how you apply the above technique to Microsoft API:

_CrtMemState m1;
_CrtMemCheckpoint( &m1 );

 //COM object creation

_CrtMemState m2;
_CrtMemCheckpoint( &m2 );

_CrtMemState difference;
_CrtMemDifference(&difference, &m1,&m2);

The object difference tells the size of COM object. You can print its value as:

_CrtMemDumpStatistics( &difference );

Or, you can further analyse the object difference which is of type _CrtMemState defined as:

//crtdbg.h

struct _CrtMemBlockHeader;
typedef struct _CrtMemState
{
    struct _CrtMemBlockHeader * pBlockHeader;
    size_t lCounts[_MAX_BLOCKS];
    size_t lSizes[_MAX_BLOCKS];
    size_t lHighWaterCount;
    size_t lTotalCount;
} _CrtMemState;

Read the documentation at MSDN:

• Memory State Comparison