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);

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