libxml2常用函数

1.创建文件时常用的函数及其作用
创建xml文档中需要：新建文件、新建节点、设置节点内容、设置节点属性、建立节点之间的关系、保存文档等；
（1）xmlNewDoc()
原型：xmlDocPtr xmlNewDoc (const xmlChar *version);
参数：version : xmlChar string giving the version of XML “1.0”
返回值：Returns : a new document
功能：生成一个xml文档

（2）xmlNewNode()
函数原型：xmlNodePtr xmlNewNode (xmlNsPtr ns, const xmlChar *name);
参数： ns : namespace if any
name : the node name
返回值：Returns : a pointer to the new node object.
功能：Creation of a new node element. ns is optional (NULL).

（3）xmlNodeSetContent ()
函数原型：void xmlNodeSetContent (xmlNodePtr cur, const xmlChar *content);
参数：cur : the node being modified
content : the new value of the content
功能：Replace the content of a node.

(4)xmlNewProp ()
函数原型：xmlAttrPtr xmlNewProp (xmlNodePtr node, const xmlChar *name, const xmlChar *value);
参数：node : the holding node
name : the name of the attribute
value : the value of the attribute
返回值：Returns : a pointer to the attribute
功能：Create a new property carried by a node.

(5)xmlAddChild ()
xmlNodePtr xmlAddChild (xmlNodePtr parent, xmlNodePtr cur);
参数：parent : the parent node
cur : the child node
返回值：Returns : the child or NULL in case of error.
功能：将一个节点设置为另外一个节点的子节点

(6)xmlDocSetRootElement ()
函数原型：xmlNodePtr xmlDocSetRootElement (xmlDocPtr doc, xmlNodePtr root);
参数：doc : the document
root : the new document root element
Returns : the old root element if any was found
功能：Set the root element of the document (doc->children is a list containing possibly comments, PIs, etc …).
设置某个节点为整个文档的根节点

(7)xmlDocDumpMemory ()
函数原型：void xmlDocDumpMemory (xmlDocPtr cur,xmlChar **mem,int *size);
参数：cur : the document
mem : OUT: the memory pointer
size : OUT: the memory length
功能：Dump an XML document in memory and return the xmlChar * and it’s size. It’s up to the caller to free the memory with xmlFree().
将生成的xml DOM树保存到内存中（不是硬盘）

(8)xmlDocDumpFormatMemory ()
void xmlDocDumpFormatMemory (xmlDocPtr cur,xmlChar **mem, int *size,int format);
与xmlDocDumpMemory ()类似，区别在于可以选择保存的格式
此系列函数还包括：
xmlDocDump、xmlDocDumpFormatMemoryEnc、 xmlDocDumpMemory、xmlDocDumpMemoryEnc、xmlDocFormatDump

(9)xmlSaveFormatFileEnc ()
函数原型：int xmlSaveFormatFileEnc (const char *filename,xmlDocPtr cur,const char *encoding,int format);
参数：filename : the filename or URL to output
cur : the document being saved
encoding : the name of the encoding to use or NULL.
format : should formatting spaces be added.
Returns : the number of bytes written or -1 in case of error.
功能：将xml文件保存在硬盘
此系列的函数还包括：xmlSaveFileEnc
特别注意一种情况：将xml形式的字符串转换为xml文档的函数xmlParseMemory()和xmlParseDoc();

2.解析xml文档
解析xml文档的过程中可能有的操作：将文件导入、获得节点的属性、获得节点的内容、
(1)获得节点内容函数xmlNodeGetContent ()
函数原型：xmlChar* xmlNodeGetContent (xmlNodePtr cur);
参数： cur : the node being read
返回值：Returns : a new xmlChar * or NULL if no content is available. It’s up to the caller to free the memory with xmlFree().
功能：Read the value of a node, this can be either the text carried directly by this node if it’s a TEXT node or the aggregate string of the values carried by this node child’s (TEXT and ENTITY_REF). Entity references are substituted.

（2）获得节点属性函数xmlGetProp ()
函数原型：xmlChar* xmlGetProp (xmlNodePtr node,const xmlChar *name);
参数：node : the node
name : the attribute name
返回值：Returns : the attribute value or NULL if not found. It’s up to the caller to free the memory with xmlFree().
功能：Search and get the value of an attribute associated to a node This does the entity substitution. This function looks in DTD attribute declaration for FIXED or default declaration values unless DTD use has been turned off.

（3）读入xml字符形式的文件xmlReadfile()
使用xmlSaveFormatFileEnc()将xml文档存为文件之后，可以使用xmlReadfile读入
xmlDocPtr doc=xmlReadFile(szDocname,”UTF-8”,XML_PARSE_RECOVER);
doc = xmlReadFile(szDocName, “GB2312”, XML_PARSE_RECOVER);//以GB2312的编码方式读入解析文件

(4)获得根节点
xmlNodePtr xmlDocGetRootElement(xmlDocPtr doc)

(5)设置xml文档的上下文指针
context = xmlXPathNewContext(pdoc);

（6）计算满足xpath表达式的节点
result = xmlXPathEvalExpression(xpath, context);

相关链接：http://www.open-open.com/lib/view/open1422537148658.html
http://blog.csdn.net/iamlate/article/details/6955698
http://blog.csdn.net/hanchaoman/article/details/42557195
http://blog.chinaunix.net/uid-114518-id-2873824.html