C++下基于COM的XML格式字符串解析，生成

现在，XML格式字符串广泛应用于各种信息的交互。不论你是做网络开发，还是桌面应用程序开发，甚至是游戏开发，都会不可避免的碰到XML格式的字符串，今天这篇文章来介绍一下在C++语言下，基于COM的XML字符串的解析与生成。

首先这里要明确两个基本概念，一个是COM,一个是XML格式。

先来说COM，COM的全称是Component Object model，组件对象模型，OMG（ObjectManagementGroup）为了实现把复杂的应用程序分割成一个个功能单一，规模较小的组件，来越来越复杂化的程序功能，发布了CORBA(Common Object Request Breaker Architecture)标准，这个标准在unix下执行，而在windows下，这套标准就是COM。详细的说明可以在我的另一篇博文：http://blog.csdn.net/crich_moon/article/details/6614392中找到。

再来简单介绍一下XML，XML（Extensible Markup Language）即可扩展标记语言，它与HTML一样，都是SGML(Standard Generalized Markup Language,标准通用标记语言)。Xml是Internet环境中跨平台的，依赖于内容的技术，是当前处理结构化文档信息的有力工具。扩展标记语言XML是一种简单的数据存储语言，使用一系列简单的标记描述数据，而这些标记可以用方便的方式建立，虽然XML占用的空间比二进制数据要占用更多的空间，但XML极其简单易于掌握和使用。

接下来先看一下如何用COM组件实现对XML格式字符串的解析。

首先需要包含头文件

#include <windows.h>

#include <msxml.h>

然后在头文件中定义类，声明类的成员函数：

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;

};

然后在CPP文件中定义成员函数的实现：

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;

}