C++中处理XML文件

类别:.NET开发 点击:0 评论:0 推荐:

写Unmanaged Code在.NET时代成为一种很悲惨的事,当你需要处理XML文件时,这种感觉会变得尤其强烈。FCL中的System.Xml多简单啊,连Steve Ballmer都知道怎么用。

事情不会总是那么理想的,如果你要在C/C++程序里处理XML怎么办呢?

选择一:市面上的XML lib还是有几个的,最有名的当然是libxml。我一年前用过,很不错,我还特意写了一份简明教程,后来不知搁哪儿了。

选择二:MS的MSXML,我要介绍的就是这个。

先说一下在MSDN哪里找文档吧,往下看的时候也好有个参考:在Index里打:Windows Media Services 9 Series SDK=>Programming Reference=>Programming Reference (C++)=>XML DOM Interfaces (C++)。什么?Windows Media?呵呵,不错,我觉得这个guide反而是最清楚的,你直接找MSXML,得到的结果,我觉得还没这个好。

在C程序里调用MSXML基本就是一堆COM接口,不过在Visual Studio里操作先要做点简单的设置:

在你的Project里Add References=>COM标签=>Microsoft XML v4.0,5.0其实也有了,但因为是和Office一起发布的,觉得有点怪,不想用,反正也未必用什么很怪异的功能,4.0可以了。

然后在加入这两行:

#include <msxml2.h>
#import <msxml4.dll>

头文件和dll库。什么?在哪里加?头文件或者c/cpp文件啊,哪里合适放哪儿。

然后就开始编程了,先定义两个必用的变量:

IXMLDOMDocumentPtr xmlFile = NULL;
IXMLDOMElement* xmlRoot = NULL;

为什么是必用的?  汗...

第一步当然是初始化COM:

if(FAILED(CoInitialize(NULL))) ....

接下来初始化xmlFile对象:

if(FAILED(xmlFile.CreateInstance("Msxml2.DOMDocument.4.0"))) ...

然后就可以加载xml文件了:

_variant_t varXml(L"C:\\test.xml");  //L for unicode
VARIANT_BOOL varOut;
xmlFile->load(varXml, &varOut);

取得root element:

xmlFile->get_documentElement(&xmlRoot))

取得第一级element:

IXMLDOMNodeList* xmlChildNodes = NULL;
xmlRoot->get_childNodes(&xmlChildNodes);

遍历所有第一级element:

IXMLDOMNode* currentNode = NULL;
while(!FAILED(xmlChildNodes->nextNode(&currentNode)) && currentNode != NULL)
{
    //do something
}

取得当前element的名称:

BSTR nodeName;
currentNode->get_nodeName(&nodeName);

取得当前element的一个attribute(假设这个attribute叫type)的值:

IXMLDOMNamedNodeMap* attributes = NULL;
IXMLDOMNode* attributeName = NULL;
_bstr_t bstrAttributeName = "type";
BSTR nameVal;
currentNode->get_attributes(&attributes);
attributes->getNamedItem(bstrAttributeName, &attributeName);
attributeName->get_text(&nameVal);

需要注意的是,你要记住释放所有的借口,IXMLDOM***->Release(),这可不是.NET,有人帮你GC,你得自己调用Release()来减reference count,it's COM, remember?

好了,大致就这样,顺便提一下XPath:

_bstr_t bstrXmlQuery = L"/books/book[@type=scifi and @author=fox]";
IXMLDOMNodeList* nodes = NULL;
if(FAILED(xmlRoot->selectNodes(bstrXmlQuery, &nodes)) || FAILED(nodes->get_length(&length)) || length == 0)
  //no match found or something went wrong
else
  //match found

上面是找这样的node:

<books>
    <book type="scifi" author="fox">....
    </book>
....
</books>

具体的XPath语法就查手册吧,到处都有。

哦,对了,忘了说:如果你全部用ATL的类的话,借口的调用会简单一点,不过很容易转换的,比如:

IXMLDOMDocument* 对应 IXMLDOMDocumentPtr(我这里用了),其他基本也是加个Ptr,我不废话了。

最后提供一个sample,我临时攒的。工作的时候写的程序当然不能拿来贴的,呵呵。这个sample基本就是遍历整个xml,然后报告一遍文件的结构,对每个node,如果它有一个叫id的attribute,就同时打印id的值。If you want the complete VS project, shoot me an email.  But I guess no one really needs it anyway, right, :  )

#include "stdafx.h"
#include <windows.h>
#include <msxml2.h>
#import <msxml4.dll>

HANDLE logFile = NULL;

#define INDENT  4

#define TESTHR(hr) \
{ \
 if(FAILED(hr)) goto fail; \
}

void PrintChild(IXMLDOMNodeList* nodeList, int level)
{
 if(nodeList == NULL)
  return;

 IXMLDOMNode* currentNode = NULL;
 IXMLDOMNodeList* childNodes = NULL;
 IXMLDOMNamedNodeMap* attributes = NULL;
 IXMLDOMNode* attributeID = NULL;

 while(!FAILED(nodeList->nextNode(&currentNode)) && currentNode != NULL)
 {
  BSTR nodeName;
  TESTHR(currentNode->get_nodeName(&nodeName));
  DWORD dwBytesWritten;
  for(int i=0; i<level*INDENT; i++)
   WriteFile(logFile, L" ", (DWORD)(sizeof(WCHAR)), &dwBytesWritten, NULL);

  //WCHAR msg[MAX_SIZE];
  //wsprintf(msg, L"%s ", nodeName);
  WriteFile(logFile, nodeName, (DWORD)(wcslen(nodeName)*sizeof(WCHAR)), &dwBytesWritten, NULL);
  
  TESTHR(currentNode->get_attributes(&attributes));
  if(attributes!=NULL)
  {
   _bstr_t bstrAttributeName = "id";
   BSTR idVal;
   TESTHR(attributes->getNamedItem(bstrAttributeName, &attributeID));
   if(attributeID != NULL)
   {
    TESTHR(attributeID->get_text(&idVal));
    WriteFile(logFile, L" ", (DWORD)(sizeof(WCHAR)), &dwBytesWritten, NULL);
    WriteFile(logFile, idVal, (DWORD)(wcslen(idVal)*sizeof(WCHAR)), &dwBytesWritten, NULL);
    WriteFile(logFile, L"\r\n", (DWORD)(2*sizeof(WCHAR)), &dwBytesWritten, NULL);
    attributeID->Release(); attributeID = NULL;
   }
   else
   {
    WriteFile(logFile, L"\r\n", (DWORD)(2*sizeof(WCHAR)), &dwBytesWritten, NULL);
   }
   attributes->Release(); attributes = NULL;

  }
  else
  {
   WriteFile(logFile, L"\r\n", (DWORD)(2*sizeof(WCHAR)), &dwBytesWritten, NULL);
  }
  
  TESTHR(currentNode->get_childNodes(&childNodes));
  PrintChild(childNodes, level+1);
  currentNode=NULL;
 }

fail:
 if(childNodes!=NULL)
  childNodes->Release();
 if(attributeID!=NULL)
  attributeID->Release();
 if(attributes!=NULL)
  attributes->Release();
 if(currentNode != NULL)
  currentNode->Release();
}

int _tmain(int argc, _TCHAR* argv[])
{
 
 IXMLDOMDocumentPtr xmlFile = NULL;
 IXMLDOMElement* xmlRoot = NULL;
 _variant_t varXml(L"C:\\demo1.xml");

 logFile = CreateFile(L"log.txt", GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
 if(logFile == INVALID_HANDLE_VALUE)
  goto fail;

 TESTHR(CoInitialize(NULL));

 TESTHR(xmlFile.CreateInstance("Msxml2.DOMDocument.4.0"));

 VARIANT_BOOL varOut;
 TESTHR(xmlFile->load(varXml, &varOut));

 TESTHR(xmlFile->get_documentElement(&xmlRoot));

 BSTR rootName;
 DWORD dwBytesWritten;
 TESTHR(xmlRoot->get_nodeName(&rootName));
 WriteFile(logFile, rootName, (DWORD)(wcslen(rootName)*sizeof(WCHAR)), &dwBytesWritten, NULL);
 WriteFile(logFile, L"\r\n", (DWORD)(2*sizeof(WCHAR)), &dwBytesWritten, NULL);

 IXMLDOMNodeList* xmlChildNodes = NULL;
 TESTHR(xmlRoot->get_childNodes(&xmlChildNodes));

 PrintChild(xmlChildNodes, 2);

fail:
 if(logFile != INVALID_HANDLE_VALUE)
  CloseHandle(logFile);
 if(xmlChildNodes!=NULL)
  xmlChildNodes->Release();
 if(xmlRoot!=NULL)
  xmlRoot->Release();
 return 0;
}

 

 

 

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