vc中使用MSXML2的注意点

MSXML2能够很好地处理xml文件，不过也有些需要注意的点

1. MSXML2的加载和释放

loadIndexXml(TCHAR * indexdir) {

if (NULL == indexdir){

return NULL;

}

::CoInitialize(NULL);

MSXML2::IXMLDOMDocumentPtr doc;

doc.CreateInstance(__uuidof(DOMDocument60));

if (VARIANT_FALSE == doc->load(indexdir)){

doc.Release();

return NULL;

}

......do smthing();

doc.Release();

CoUninitialize();

2. 新建一个xml文件

CString setnameindex;

setnameindex.Format("./xxx/%s.xml", name);

//判断文件是否存在

HANDLE hOpenFile = (HANDLE)CreateFile(setnameindex, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, NULL, NULL);

if (hOpenFile == INVALID_HANDLE_VALUE) {

::CoInitialize(NULL);

MSXML2::IXMLDOMDocumentPtr setnamedoc;

setnamedoc.CreateInstance(__uuidof(DOMDocument60));

char* dbfile = (LPSTR)(LPCSTR)setnameindex;

setnamedoc->preserveWhiteSpace = VARIANT_TRUE;//这个必须设置，不然不生效

MSXML2::IXMLDOMProcessingInstructionPtr pProInstruction = NULL;

pProInstruction = setnamedoc->createProcessingInstruction((_bstr_t)(char*)"xml", (_bstr_t)(char*)"version="1.0" encoding="utf-8"");

((MSXML2::IXMLDOMNodePtr)setnamedoc)->appendChild(pProInstruction);

MSXML2::IXMLDOMElementPtr pRootElement = NULL;

pRootElement = setnamedoc->createElement((_bstr_t)(char*)"db");

setnamedoc->PutRefdocumentElement(pRootElement);

((MSXML2::IXMLDOMNodePtr)setnamedoc->documentElement)->appendChild(setnamedoc->createTextNode(" "));

MSXML2::IXMLDOMCommentPtr pComment = setnamedoc->createComment((_bstr_t)(char*)"db");

((MSXML2::IXMLDOMNodePtr)pRootElement)->appendChild(pComment); // 注释

setnamedoc->save((LPSTR)(LPCSTR)setnameindex);

setnamedoc.Release();

//CoUninitialize();

}

3.获取某个节点列表，判断节点是否存在，并做处理

MSXML2::IXMLDOMNodeListPtr node_person_list = ((MSXML2::IXMLDOMNodePtr)doc)->selectNodes("register/person");

if (NULL == node_person_list || node_person_list->Getlength() == 0) {

........不存在的情况

}

else{

........存在的情况

}

xml文件：

....

</register>

4. 获取节点属性如name file data

MSXML2::IXMLDOMNodeListPtr node_person_list = ((MSXML2::IXMLDOMNodePtr)doc)->selectNodes("register/person");

for (int i = 0; i < node_person_list->Getlength(); i++)

{

MSXML2::IXMLDOMNodePtr node_item = node_person_list->Getitem(i);

_variant_t var_name = ((MSXML2::IXMLDOMElementPtr)node_item)->getAttribute("name");

_variant_t var_file = ((MSXML2::IXMLDOMElementPtr)node_item)->getAttribute("file");

_variant_t var_date = ((MSXML2::IXMLDOMElementPtr)node_item)->getAttribute("date");

_variant_t var_score = NULL;

var_score = ((MSXML2::IXMLDOMElementPtr)node_item)->getAttribute("score");

n->name = _tcsdup(CString(var_name.bstrVal));

//n->score = wcstol(var_score.bstrVal, NULL, 0);

TCHAR temp[1024];

//_tcscpy(temp, TEXT("facescore/woman/"));

_tcscpy(temp, TEXT(""));

_tcscat(temp, CString(var_file.bstrVal));

n->file = _tcsdup(temp);

//n->feature = (float *)malloc(sizeof(float) * 2048);

n->date = _ttoi((LPCTSTR)(_bstr_t)var_date);

if (var_score.vt != VT_NULL) {

n->score = _ttoi((LPCTSTR)(_bstr_t)var_score);

}

else {

n->score = -1;

}

lw->AddTail(n);

}

其中 var_score取出来后，不知道判断是不是取到了正确的值，不能直接使用，错误使用会导致崩溃，判断的方法如下：

if (var_score.vt != VT_NULL) {

n->score = _ttoi((LPCTSTR)(_bstr_t)var_score);

}

5.删除某个节点，并保存

CString dbxml;

dbxml.Format("./xxx/%s.xml", name);

::CoInitialize(NULL);

MSXML2::IXMLDOMDocumentPtr doc;

doc.CreateInstance(__uuidof(DOMDocument60));

if (VARIANT_FALSE == doc->load(((LPSTR)(LPCSTR)dbxml))) {

doc.Release();

return 2;

}

time_t t = time(nullptr);

MSXML2::IXMLDOMNodePtr item;

CString str;

str.Format("db/item[@name='%s']", name);

//_variant_t var(str);

item = ((MSXML2::IXMLDOMNodePtr)doc)->selectSingleNode(_bstr_t(str));

if (item != NULL) {

item->GetparentNode()->removeChild(item);

}

doc->save((LPSTR)(LPCSTR)dbxml);

doc.Release();

CoUninitialize();

6.更新xml里面某些节点的数据（先删除，再添加）

str.Format("db/item[@name='%s']/features/feature", duq.name);

//_variant_t var(str);

feature = ((MSXML2::IXMLDOMNodePtr)doc)->selectSingleNode(_bstr_t(str));

if (feature != NULL) {

((MSXML2::IXMLDOMElementPtr)feature)->setAttribute("date", t);

MSXML2::IXMLDOMNodeList *pNodeList = NULL;

feature->get_childNodes(&pNodeList);

Debug_TraceA("UpdataSingleItemToDbXML get_childNodes ");

if (pNodeList != NULL) {

for (int i = 0; i < pNodeList->Getlength(); i++) {

MSXML2::IXMLDOMNodePtr pNode;

pNodeList->get_item(i, &pNode);

feature->removeChild(pNode);

}

for (int i = 0; i < feature_size; i++) {

MSXML2::IXMLDOMNodePtr node_float = doc->createElement("f");

CString s;

s.Format("%.8f", userfeature[i]);

_variant_t var(s);

node_float->put_text(_bstr_t(s));

//node_float->nodeValue.fltVal = p->feature[i];// CComVariant(p->feature[i]);

feature->appendChild(node_float);

}

doc->save(dbxml);

doc.Release();

CoUninitialize();

7.msxml在save的时候报错，如果路径没问题，很有可能在别的地方有xml文件的引用没有释放，必须提前释放

    try {
    doc->save((LPSTR)(LPCSTR)dbxml);
    }
    catch (_com_error errorObject){
    Debug_TraceA("Exception, HRESULT = %d  %s 
", errorObject.Error(), (LPCTSTR)errorObject.Description());
    }

可以通过上面代码查看异常

msxml坑多浪急

        MSXML2::IXMLDOMNodeList *pNodeList = NULL;
        feature->get_childNodes(&pNodeList);
        
        if (pNodeList != NULL) {
            
            //Debug_TraceA("pNodeList->Getlength() %d  %d 
", pNodeList->Getlength(), feature->GetchildNodes()->length);
            //MSXML2::IXMLDOMNodePtr pNode;
            //while (pNode = pNodeList->nextNode() != NULL) {
            //    feature->removeChild(pNode);
            //}
            for (int i = pNodeList->Getlength()-1; i >=0; i--) {
                MSXML2::IXMLDOMNodePtr pNode;
                pNodeList->get_item(i, &pNode);
                feature->removeChild(pNode);
            }
        }

这是正常的代码

这是错误的代码，因为pNodeList和feature是关联的，从前面removeChild，pNodeList->Getlength()的值在变小，每执行一次，任意一个子节点就向前移动一位，位置下标就减小1，而i是一直累加的所以会出问题

   MSXML2::IXMLDOMNodeList *pNodeList = NULL;
        feature->get_childNodes(&pNodeList);
        
        if (pNodeList != NULL) {
            
            //Debug_TraceA("pNodeList->Getlength() %d  %d 
", pNodeList->Getlength(), feature->GetchildNodes()->length);
      
            for (int i = 0; i <pNodeList->Getlength(); i++) {
                MSXML2::IXMLDOMNodePtr pNode;
                pNodeList->get_item(i, &pNode);
                feature->removeChild(pNode);
            }
        }

同理这个也是错的

        MSXML2::IXMLDOMNodeList *pNodeList = NULL;
        feature->get_childNodes(&pNodeList);
        
        if (pNodeList != NULL) {
            
            //Debug_TraceA("pNodeList->Getlength() %d  %d 
", pNodeList->Getlength(), feature->GetchildNodes()->length);
            MSXML2::IXMLDOMNodePtr pNode;
            while (pNode = pNodeList->nextNode() != NULL) {
                feature->removeChild(pNode);
            }

        }

vc中使用MSXML2的注意点

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