Source: queryNodes.cpp

This example application calls both the selectSingleNode method and the selectNodes method on an XML DOM object loaded from the stocks.xml file. The same XPath expression is input to both methods:

//stock[1]/*

This expression specifies all the child elements of the first <stock> element in the XML document. In MSXML, the selectSingleNode method returns the first element of the resultant node-set, and the selectNodes method returns all the elements in the node-set.

Programmatically, this source code performs the following steps:

1. Creates an instance of an XML DOM object (pXMLDom).
2. Calls the load method on pXMLDom to load XML data from a file (stocks.xml).
3. Calls the selectSingleNode method on pXMLDom to select a DOM node according to the input XPath expression (//stock[1]/*). Then displays the resulting node in the console if the query is successful.
4. Calls the selectNodes method on pXMLDom to select a DOM node-set according to the input XPath expression ("//stock[1]/*"). Then displays the resulting nodes in the console if the query is successful.

C/C++ Source File (queryNodes.cpp)

#include <stdio.h>
#include <windows.h>
#import <msxml5.dll> raw_interfaces_only
using namespace MSXML2;

// Macro that calls a COM method returning HRESULT value:
#define HRCALL(a, errmsg) \
do { \
    hr = (a); \
    if (FAILED(hr)) { \
        dprintf( "%s:%d  HRCALL Failed: %s\n  0x%.8x = %s\n", \
                __FILE__, __LINE__, errmsg, hr, #a ); \
        goto clean; \
    } \
} while (0)

// Helper function that put output in stdout and debug window
// in Visual Studio:
void dprintf( char * format, ...)
{
    static char buf[1024];
    va_list args;
    va_start( args, format );
    vsprintf( buf, format, args );
    va_end( args);
    OutputDebugStringA( buf);
    printf("%s", buf);
}

// Helper function to create a DOM instance: 
IXMLDOMDocument * DomFromCOM()
{
   HRESULT hr;
   IXMLDOMDocument *pxmldoc = NULL;

    HRCALL( CoCreateInstance(__uuidof(DOMDocument50),
                      NULL,
                      CLSCTX_INPROC_SERVER,
                      __uuidof(IXMLDOMDocument),
                      (void**)&pxmldoc),
            "Create a new DOMDocument");

    HRCALL( pxmldoc->put_async(VARIANT_FALSE),
            "should never fail");
    HRCALL( pxmldoc->put_validateOnParse(VARIANT_FALSE),
            "should never fail");
    HRCALL( pxmldoc->put_resolveExternals(VARIANT_FALSE),
            "should never fail");

   return pxmldoc;
clean:
   if (pxmldoc)
    {
      pxmldoc->Release();
    }
   return NULL;
}

VARIANT VariantString(BSTR str)
{
   VARIANT var;
   VariantInit(&var);
   V_BSTR(&var) = SysAllocString(str);
   V_VT(&var) = VT_BSTR;
   return var;
}

void ReportParseError(IXMLDOMDocument *pDom, char *desc) {
   IXMLDOMParseError *pXMLErr=NULL;
   BSTR bstrReason = NULL;
   HRESULT hr;
   HRCALL(pDom->get_parseError(&pXMLErr),
            "dom->get_parseError: ");
   HRCALL(pXMLErr->get_reason(&bstrReason),
            "parseError->get_reason: ");
   
   dprintf("%s %S\n",desc, bstrReason);
clean:
   if (pXMLErr) pXMLErr->Release();
   if (bstrReason) SysFreeString(bstrReason);
}

int main(int argc, char* argv[])
{
   IXMLDOMDocument *pXMLDom=NULL;
   IXMLDOMNodeList *pNodes=NULL;
   IXMLDOMNode *pNode=NULL;
   BSTR bstr = NULL;
   VARIANT_BOOL status;
   VARIANT var;
   HRESULT hr;
   long length;

   CoInitialize(NULL);

   pXMLDom = DomFromCOM();
   if (!pXMLDom) goto clean;

   VariantInit(&var);
   var = VariantString(L"stocks.xml");
   HRCALL(pXMLDom->load(var, &status), "dom->load(): ");

   if (status!=VARIANT_TRUE) {
      ReportParseError(pXMLDom, 
         "Failed to load DOM from stocks.xml");
      goto clean;
   }

   // Query a single node.
   if (bstr) SysFreeString(bstr);
   bstr = SysAllocString(L"//stock[1]/*");
   HRCALL(pXMLDom->selectSingleNode(bstr, &pNode),
      "dom->selectSingleNode: ");
   if (!pNode) {
      ReportParseError(pXMLDom, "Calling selectSingleNode ");
   }
   else {
      dprintf("Result from selectSingleNode:\n");
      if (bstr) SysFreeString(bstr);
      HRCALL(pNode->get_nodeName(&bstr)," get_nodeName ");
      dprintf("Node, <%S>:\n", bstr);
      if (bstr) SysFreeString(bstr);
      HRCALL(pNode->get_xml(&bstr), "get_xml: ");
      dprintf("\t%S\n\n", bstr);
   }

   // Query a node-set.
   if (bstr) SysFreeString(bstr);
   bstr = SysAllocString(L"//stock[1]/*");
   HRCALL(pXMLDom->selectNodes(bstr, &pNodes), "selectNodes ");
   if (!pNodes) {
      ReportParseError(pXMLDom, "Error while calling selectNodes ");
   }
   else {
      dprintf("Results from selectNodes:\n");
      HRCALL(pNodes->get_length(&length), "get_length: ");
      for (long i=0; i<length; i++) {
         if (pNode) pNode->Release();
         HRCALL(pNodes->get_item(i, &pNode), "get_item: ");
         if (bstr) SysFreeString(bstr);
         HRCALL(pNode->get_nodeName(&bstr), "get_nodeName: ");
         dprintf("Node (%d), <%S>:\n",i, bstr);
         SysFreeString(bstr);
         HRCALL(pNode->get_xml(&bstr), "get_xml: ");
         dprintf("\t%S\n", bstr);
      }
   }

clean:
   if (bstr) SysFreeString(bstr);
   if (&var) VariantClear(&var);
   if (pXMLDom) pXMLDom->Release();
   if (pNodes) pNodes->Release();
   if (pNode) pNode->Release();

   CoUninitialize();
   return 0;
}

To add queryNodes.cpp to the project

1. Select FileView on the project browser, and highlight queryNodeProj files. From the File menu, select New.
2. On the Files tab of the New dialog box, highlight C++ Source File. Then type "queryNodes.cpp" in the File name text box, and click OK.
3. Copy the C/C++ source code above and paste it into the source file you just created.

Next, we'll add the resource file to the queryNodes project.