[转载]C++中处理XML文件

 

　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，假如你要在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: est.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); 

需要注重的是，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：假如你全部用ATL的类的话，借口的调用会简单一点，不过很轻易转换的，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，假如它有一个叫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" ", (Dword)(2*sizeof(WCHAR)), &dwBytesWritten, NULL); 
attributeID->Release(); attributeID = NULL; 
} 
else 
{ 
WriteFile(logFile, L" ", (Dword)(2*sizeof(WCHAR)), &dwBytesWritten, NULL); 

} 
attributes->Release(); attributes = NULL; 

} 
else 
{ 
WriteFile(logFile, L" ", (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" ", (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 
 

 

原文来自
http://school.cnd8.com/c/jiaocheng/10145.htm