Howto Use XmlLite

I was recently breaking off high-level heavy-weight dependencies on a code I was cleaning up, and I ran into the 500 lb. gorilla that is MSXML6. I found some code that was using it to parse some basic XML strings. MSXML is a full featured XML parser that can do fancy things like schema validation, but it is kind of heavy weight and has high-level dependencies. The downsides of MSXML might be a necessary evil if you need its fancy features, but in many cases we don’t. In my code, I definitely did not. I wanted to gut XML out altogether, but was vetoed. My thoughts turned to MSXML’s handsome and more athletic cousin, XmlLite. XmlLite has very few dependencies and is self-contained in its own library files. Although XmlLite is COM like, it doesn’t even actually have a dependency on COM, so I am liking this guy already. It does need an IStream, or an ISequentialStream, so you will have to create one from some file, or implement the interface yourself. I can provide a sample implementation of that later.


To the code…


Here is a simple quick and dirty code I wrote mainly following the code samples on MSDN. This program takes a filename as a parameter, opens it, and parses the XML printing out the elements. The code I actually wrote looks cleaner, but this will get you going.


MSDN Refrences


MSXML6


XmlLite

/*
 * xml_lite.cpp
 *
 * Description : simple code to show using XML Lite
 */

#include <objbase.h>
#include <XmlLite.h>
#include <shlwapi.h>
#include <stdio.h>

HRESULT WriteAttributes(IXmlReader* pReader)
{
    const WCHAR* pwszPrefix;
    const WCHAR* pwszLocalName;
    const WCHAR* pwszValue;
    HRESULT hr = pReader->MoveToFirstAttribute();

    if (S_FALSE == hr)
        return hr;
    if (S_OK != hr)
    {
        wprintf(L"Error moving to first attribute, error is %08.8lx", hr);
        return -1;
    }
    else
    {
        while (TRUE)
        {
            if (!pReader->IsDefault())
            {
                UINT cwchPrefix;
                if (FAILED(hr = pReader->GetPrefix(&pwszPrefix, &cwchPrefix)))
                {
                    wprintf(L"Error getting prefix, error is %08.8lx", hr);
                    return -1;
                }
                if (FAILED(hr = pReader->GetLocalName(&pwszLocalName, NULL)))
                {
                    wprintf(L"Error getting local name, error is %08.8lx", hr);
                    return -1;
                }
                if (FAILED(hr = pReader->GetValue(&pwszValue, NULL)))
                {
                    wprintf(L"Error getting value, error is %08.8lx", hr);
                    return -1;
                }
                if (cwchPrefix > 0)
                    wprintf(L"Attr: %s:%s=\"%s\" \n", pwszPrefix, pwszLocalName, pwszValue);
                else
                    wprintf(L"Attr: %s=\"%s\" \n", pwszLocalName, pwszValue);
            }

            if (S_OK != pReader->MoveToNextAttribute())
                break;
        }
    }
    return hr;
}

int __cdecl wmain(
        __in int argc, 
        __in_ecount(argc) LPCTSTR argv[])
{
    HRESULT hr = S_OK;
    IStream *pStream = NULL;
    IXmlReader *pReader = NULL;
    UINT cAttribute = 0;

    if (FAILED(hr = SHCreateStreamOnFile(argv[1], STGM_READ, &pStream)))
    {
        wprintf(L"Error creating file reader, error is %08.8lx", hr);
        return hr;
    }

    if (FAILED(hr = CreateXmlReader(__uuidof(IXmlReader), (void**) &pReader, NULL)))
    {
        wprintf(L"error creating xml reader, error is %08.8lx", hr);
        return hr;
    }

    if (FAILED(hr = pReader->SetProperty(XmlReaderProperty_DtdProcessing, DtdProcessing_Prohibit)))
    {
        wprintf(L"Error setting XmlReaderProperty_DtdProcessing, error is %08.8lx", hr);
        return -1;
    }

    if (FAILED(hr = pReader->SetInput(pStream)))
    {
        wprintf(L"Error setting input for reader, error is %08.8lx", hr);
        return -1;
    }

    XmlNodeType nodeType;

    while (S_OK == (hr = pReader->Read(&nodeType)))
    {
        LPCWSTR pwszPrefix = NULL;
        UINT cwchPrefix = 0;
        LPCWSTR pwszLocalName = NULL;
        LPCWSTR pwszValue = NULL;

     switch (nodeType)
  {
  case XmlNodeType_XmlDeclaration:
   wprintf(L"XmlDeclaration\n");
   if (FAILED(hr = WriteAttributes(pReader)))
   {
    wprintf(L"Error writing attributes, error is %08.8lx", hr);
    return -1;
   }
   break;
  case XmlNodeType_Element:
   if (FAILED(hr = pReader->GetPrefix(&pwszPrefix, &cwchPrefix)))
   {
    wprintf(L"Error getting prefix, error is %08.8lx", hr);
    return -1;
   }
   if (FAILED(hr = pReader->GetLocalName(&pwszLocalName, NULL)))
   {
    wprintf(L"Error getting local name, error is %08.8lx", hr);
    return -1;
   }
   if (cwchPrefix > 0)
    wprintf(L"Element: %s:%s\n", pwszPrefix, pwszLocalName);
   else
    wprintf(L"Element: %s\n", pwszLocalName);

   if (FAILED(hr = WriteAttributes(pReader)))
   {
    wprintf(L"Error writing attributes, error is %08.8lx", hr);
    return -1;
   }

   if (pReader->IsEmptyElement() )
    wprintf(L" (empty)");
   break;
  case XmlNodeType_EndElement:
   if (FAILED(hr = pReader->GetPrefix(&pwszPrefix, &cwchPrefix)))
   {
    wprintf(L"Error getting prefix, error is %08.8lx", hr);
    return -1;
   }
   if (FAILED(hr = pReader->GetLocalName(&pwszLocalName, NULL)))
   {
    wprintf(L"Error getting local name, error is %08.8lx", hr);
    return -1;
   }
   if (cwchPrefix > 0)
    wprintf(L"End Element: %s:%s\n", pwszPrefix, pwszLocalName);
   else
    wprintf(L"End Element: %s\n", pwszLocalName);
   break;
        /*
  case XmlNodeType_Text:
  case XmlNodeType_Whitespace:
   if (FAILED(hr = pReader->GetValue(&pwszValue, NULL)))
   {
    wprintf(L"Error getting value, error is %08.8lx", hr);
    return -1;
   }
   wprintf(L"Text: >%s<\n", pwszValue);
   break;
        */
  case XmlNodeType_CDATA:
   if (FAILED(hr = pReader->GetValue(&pwszValue, NULL)))
   {
    wprintf(L"Error getting value, error is %08.8lx", hr);
    return -1;
   }
   wprintf(L"CDATA: %s\n", pwszValue);
   break;
  case XmlNodeType_ProcessingInstruction:
   if (FAILED(hr = pReader->GetLocalName(&pwszLocalName, NULL)))
   {
    wprintf(L"Error getting name, error is %08.8lx", hr);
    return -1;
   }
   if (FAILED(hr = pReader->GetValue(&pwszValue, NULL)))
   {
    wprintf(L"Error getting value, error is %08.8lx", hr);
    return -1;
   }
   wprintf(L"Processing Instruction name:%S value:%S\n", pwszLocalName, pwszValue);
   break;
  case XmlNodeType_Comment:
   if (FAILED(hr = pReader->GetValue(&pwszValue, NULL)))
   {
    wprintf(L"Error getting value, error is %08.8lx", hr);
    return -1;
   }
   wprintf(L"Comment: %s\n", pwszValue);
   break;
  case XmlNodeType_DocumentType:
   wprintf(L"DOCTYPE is not printed\n");
   break;
  }

        /*
        hr = pReader->GetAttributeCount(&cAttribute);

        if (S_OK == hr)
        {
            wprintf(L"num attrubutes %i\n", cAttribute);
        }
        */
    }

    return hr;
}