C++下基於COM的XML格式字串解析，產生

現在，XML格式字串廣泛應用於各種資訊的互動。不論你是做網路開發，還是傳統型應用程式開發，甚至是遊戲開發，都會不可避免的碰到XML格式的字串，今天這篇文章來介紹一下在C++語言下，基於COM的XML字串的解析與產生。

首先這裡要明確兩個基本概念，一個是COM,一個是XML格式。

先來說COM，COM的全稱是Component Object model，元件物件模型，OMG（ObjectManagementGroup）為了實現把複雜的應用程式分割成一個個功能單一，規模較小的組件，來越來越複雜化的程式功能，發布了CORBA(Common Object Request Breaker Architecture)標準，這個標準在unix下執行，而在windows下，這套標準就是COM。詳細的說明可以在我的另一篇博文：http://blog.csdn.net/crich_moon/article/details/6614392中找到。

再來簡單介紹一下XML，XML（Extensible Markup Language）即可延伸標記語言 (XML)，它與HTML一樣，都是SGML(Standard Generalized Markup Language,標準通用標記語言 (SGML))。Xml是Internet環境中跨平台的，依賴於內容的技術，是當前處理結構化文檔資訊的有力工具。擴充標記語言XML是一種簡單的資料存放區語言，使用一系列簡單的標記描述資料，而這些標記可以用方便的方式建立，雖然XML佔用的空間比位元據要佔用更多的空間，但XML極其簡單易於掌握和使用。

接下來先看一下如何用COM組件實現對XML格式字串的解析。

首先需要包含標頭檔

#include <windows.h>
#include <msxml.h>

然後在標頭檔中定義類，聲明類的成員函數：

class XmlHelper
{
public:
    XmlHelper(void);
    XmlHelper(LPCTSTR XmlFileName);
    ~XmlHelper(void);

    HRESULT ReadItemValue(LPCTSTR strItem,LPCTSTR strValueName,TCHAR* pchValue,DWORD dwCount);
    HRESULT ReadItemAttributeValue(LPCTSTR strItem,LPCTSTR strValueName,LPCTSTR strAttributeName,TCHAR* strAttributeValue,DWORD dwCount);
    HRESULT WriteItemValue(LPCTSTR strRootName,LPCTSTR strItem,LPCTSTR strValueName,LPCTSTR strValue,LPCTSTR strAttributeName,LPCTSTR strAttributeValue);
private:
    BSTR m_szXmlFile;
    BSTR m_szXmlStr;
    int m_nXmlLen;
};

然後在CPP檔案中定義成員函數的實現：

XmlHelper::XmlHelper(LPCTSTR XmlFileName)
{
    if (!XmlFileName)
    {
        ASSERT(0);
    }
    else
    {
        m_szXmlFile = SysAllocString(XmlFileName);
    }
}
HRESULT XmlHelper::ReadItemValue(LPCTSTR strItem,LPCTSTR strValueName,TCHAR* pchValue,DWORD dwCount)
{
    HRESULT hr = E_FAIL;
    BSTR pText = NULL;

    IXMLDOMDocument* piXMLDoc = NULL;
    IXMLDOMElement* pRoot = NULL;

    CoCreateInstance(CLSID_DOMDocument,NULL,CLSCTX_INPROC_SERVER,IID_IXMLDOMDocument,(LPVOID*)&piXMLDoc);

    if (piXMLDoc)
    {
        piXMLDoc->put_async(VARIANT_FALSE);

        VARIANT vXmlFile;
        vXmlFile.vt = VT_BSTR;
        vXmlFile.bstrVal = (BSTR)m_szXmlFile;

        VARIANT_BOOL    vb;
        piXMLDoc->load(vXmlFile, &vb);
        if (vb)
        {
            piXMLDoc->get_documentElement(&pRoot);

            if (pRoot)
            {
                IXMLDOMNode* pMainNode = NULL;
                IXMLDOMElement* pMainNodeEle = NULL;

                pRoot->selectSingleNode((BSTR)strItem,&pMainNode);
                if (pMainNode)
                {
                    pMainNode->QueryInterface(IID_IXMLDOMElement,(VOID**)&pMainNodeEle);
                    pMainNode->Release();
                }

                if (pMainNodeEle)
                {

                    IXMLDOMNode* pValueNode = NULL;
                    IXMLDOMElement* pValueNodeEle = NULL;

                    pMainNodeEle->selectSingleNode((BSTR)strValueName,&pValueNode);
                    if (pValueNode)
                    {
                        pValueNode->QueryInterface(IID_IXMLDOMElement,(VOID**)&pValueNodeEle);
                        pValueNode->Release();
                    }
                    if (pValueNodeEle)
                    {
                        hr = pValueNodeEle->get_text(&pText);
                        pValueNodeEle->Release();
                    }
                    pMainNodeEle->Release();
                }
                pRoot->Release();
            }        
        }

        piXMLDoc->Release();
    }

    if (pText)
    {
        wcsncpy(pchValue,pText,dwCount);
        SysFreeString(pText);
    }
    return hr;

}

HRESULT XmlHelper::ReadItemAttributeValue(LPCTSTR strItem,LPCTSTR strValueName,LPCTSTR strAttributeName,TCHAR* strAttributeValue,DWORD dwCount)
{
    WaitForSingleObject(m_hSyncEvent,5000);
    HRESULT hr = E_FAIL;
    VARIANT vattri={0};

    IXMLDOMDocument* piXMLDoc = NULL;
    IXMLDOMElement* pRoot = NULL;

    CoCreateInstance(CLSID_DOMDocument,NULL,CLSCTX_INPROC_SERVER,IID_IXMLDOMDocument,(LPVOID*)&piXMLDoc);

    if (piXMLDoc)
    {
        piXMLDoc->put_async(VARIANT_FALSE);

        VARIANT vXmlFile;
        vXmlFile.vt = VT_BSTR;
        vXmlFile.bstrVal = (BSTR)m_szXmlFile;

        VARIANT_BOOL    vb;
        piXMLDoc->load(vXmlFile, &vb);
        if (vb)
        {
            piXMLDoc->get_documentElement(&pRoot);

            if (pRoot)
            {
                IXMLDOMNode* pMainNode = NULL;
                IXMLDOMElement* pMainNodeEle = NULL;

                pRoot->selectSingleNode((BSTR)strItem,&pMainNode);
                if (pMainNode)
                {
                    pMainNode->QueryInterface(IID_IXMLDOMElement,(VOID**)&pMainNodeEle);
                    pMainNode->Release();
                }

                if (pMainNodeEle)
                {

                    IXMLDOMNode* pValueNode = NULL;
                    IXMLDOMElement* pValueNodeEle = NULL;

                    pMainNodeEle->selectSingleNode((BSTR)strValueName,&pValueNode);
                    if (pValueNode)
                    {
                        pValueNode->QueryInterface(IID_IXMLDOMElement,(VOID**)&pValueNodeEle);
                        pValueNode->Release();
                    }
                    if (pValueNodeEle)
                    {
                        //hr = pValueNodeEle->get_text(&pText);

                        BSTR bstrattr = SysAllocString(strAttributeName);
                        hr = pValueNodeEle->getAttribute(bstrattr,&vattri);
                        SysFreeString(bstrattr);

                        pValueNodeEle->Release();
                    }
                    pMainNodeEle->Release();
                }
                pRoot->Release();
            }        
        }

        piXMLDoc->Release();
    }

    if (vattri.vt == VT_BSTR && vattri.bstrVal)
    {
        wcsncpy(strAttributeValue,vattri.bstrVal,dwCount);
        SysFreeString(vattri.bstrVal);
    }

    SetEvent(m_hSyncEvent);
    return hr;
}

HRESULT XmlHelper::WriteItemValue(LPCTSTR strRootName,LPCTSTR strItem,LPCTSTR strValueName,LPCTSTR strValue,LPCTSTR strAttributeName,LPCTSTR strAttributeValue)
{
    WaitForSingleObject(m_hSyncEvent,5000);
    HRESULT hr = E_FAIL;
    IXMLDOMDocument* piXMLDoc = NULL;
    IXMLDOMElement* pRoot = NULL;

    CoCreateInstance(CLSID_DOMDocument,NULL,CLSCTX_INPROC_SERVER,IID_IXMLDOMDocument,(LPVOID*)&piXMLDoc);

    if (piXMLDoc)
    {
        piXMLDoc->put_async(VARIANT_FALSE);

        VARIANT vXmlFile;
        vXmlFile.vt = VT_BSTR;
        vXmlFile.bstrVal = (BSTR)m_szXmlFile;

        VARIANT_BOOL    vb;
        piXMLDoc->load(vXmlFile, &vb);
        if (!vb)
        {
            piXMLDoc->createElement((BSTR)strRootName,&pRoot);
            if (pRoot)
            {
                piXMLDoc->appendChild(pRoot,NULL);
            }
        }

        if (!pRoot)
        {
            piXMLDoc->get_documentElement(&pRoot);
        }
        if (pRoot)
        {

            IXMLDOMNode* pMainNode = NULL;
            IXMLDOMElement* pMainNodeEle = NULL;

            pRoot->selectSingleNode((BSTR)strItem,&pMainNode);
            if (!pMainNode)
            {
                piXMLDoc->createElement((BSTR)strItem,&pMainNodeEle);
                pRoot->appendChild(pMainNodeEle,NULL);
            }
            else
            {
                pMainNode->QueryInterface(IID_IXMLDOMElement,(VOID**)&pMainNodeEle);
                pMainNode->Release();
            }

            if (pMainNodeEle)
            {

                IXMLDOMNode* pValueNode = NULL;
                IXMLDOMElement* pValueNodeEle = NULL;

                pMainNodeEle->selectSingleNode((BSTR)strValueName,&pValueNode);
                if (!pValueNode)
                {
                    piXMLDoc->createElement((BSTR)strValueName,&pValueNodeEle);
                    pMainNodeEle->appendChild(pValueNodeEle,NULL);
                }
                else
                {
                    pValueNode->QueryInterface(IID_IXMLDOMElement,(VOID**)&pValueNodeEle);
                    pValueNode->Release();
                }
                if (pValueNodeEle)
                {
                    VARIANT vut;
                    vut.vt = VT_BSTR;
                    vut.bstrVal = SysAllocString(strAttributeValue);

                    pValueNodeEle->setAttribute((BSTR)strAttributeName,vut);

                    SysFreeString(vut.bstrVal);

                    BSTR bstrValue = SysAllocString(strValue);
                    hr = pValueNodeEle->put_text(bstrValue);
                    SysFreeString(bstrValue);
                    pValueNodeEle->Release();
                }
                pMainNodeEle->Release();
            }
            pRoot->Release();
        }

        piXMLDoc->save(vXmlFile);
        piXMLDoc->Release();
    }

    SetEvent(m_hSyncEvent);
    return hr;

}