[libxml2]_[XML处理]_[使用libxml2的xpath特性修改xml文件内容]

场景：

1.在软件需要保存一些配置项时,使用数据库的话比较复杂,查看内容也不容易.纯文本文件对utf8字符支持也不好.

2.这时候使用xml是最佳选择,使用跨平台库libxml2。

3.基于xpath的保存方式对保存局部内容非常方便。

4.参考例子xpath2.c

5.实际耗时: 2小时.

文件1: Makefile

CP="cp"build-post: test.exe${CP} E:/software/Lib/file/xml-libxml2-2.7.1/win32/release/share/libxml2-2.dll .test.exe:test.og++ -o test.exe test.o -LE:/software/Lib/file/xml-libxml2-2.7.1/win32/release/share -lxml2test.o:test.cppg++ -IE:/software/Lib/file/xml-libxml2-2.7.1/win32/release/share/include -c test.cpp -o test.o

文件2：test.cpp

#include <stdio.h>#include <assert.h>#include <string>#include <iostream>#include <map>#include "libxml/tree.h"#include "libxml/parser.h"#include "libxml/xpath.h"#include "libxml/xpathInternals.h"#include "libxml/xmlsave.h"using namespace std;static void _UpdateXpathNodes(xmlNodeSetPtr nodes, const xmlChar* value) {    int size;    int i;        assert(value);    size = (nodes) ? nodes->nodeNr : 0;    for(i = size - 1; i >= 0; i--) {assert(nodes->nodeTab[i]);xmlNodeSetContent(nodes->nodeTab[i], value);if (nodes->nodeTab[i]->type != XML_NAMESPACE_DECL){nodes->nodeTab[i] = NULL;}   }}static int _UpdateWithXpath(xmlXPathContextPtr xpathCtx,const char* key,const char* value){xmlXPathObjectPtr xpathObj;    xpathObj = xmlXPathEvalExpression(BAD_CAST key, xpathCtx);    if(!xpathObj){        fprintf(stderr,"Error: unable to evaluate xpath expression \"%s\"\n", key);        return -1;    }    _UpdateXpathNodes(xpathObj->nodesetval, BAD_CAST value);    xmlXPathFreeObject(xpathObj);return 0;}static int _UpdateXml(const char* path,map<string,string>& keyValue){xmlDocPtr doc;xmlXPathContextPtr xpathCtx; doc = xmlParseFile(path);    if (!doc){fprintf(stderr, "Error: unable to parse file \"%s\"\n", path);return(-1);    }    /* Create xpath evaluation context */    xpathCtx = xmlXPathNewContext(doc);    //1.注意,这里根Node有声明xmlns,那么必须加下边这句，相应的xpath要加前缀 /c:container/c:rootfiles    //xmlXPathRegisterNs(xpathCtx,BAD_CAST"c",BAD_CAST"urn:oasis:names:tc:opendocument:xmlns:container");    if(!xpathCtx){        fprintf(stderr,"Error: unable to create new XPath context\n");        xmlFreeDoc(doc);         return(-1);    }//3.updatemap<string,string>::iterator iter;map<string,string>::iterator end = keyValue.end();for(iter = keyValue.begin();iter!= end;iter++){cout << "word: " << iter->first << ", count: " << iter->second << endl;_UpdateWithXpath(xpathCtx,iter->first.c_str(),iter->second.c_str());}xmlXPathFreeContext(xpathCtx);//4.savexmlSaveCtxtPtr saveCtxtPtx = xmlSaveToFilename(path,"UTF-8",XML_SAVE_FORMAT);if(!saveCtxtPtx){xmlFreeDoc(doc);return -1;}    if(-1 == xmlSaveDoc(saveCtxtPtx,doc)){xmlFreeDoc(doc);return -1;}xmlSaveClose(saveCtxtPtx);//xmlDocDump(stdout, doc);//5.free    xmlFreeDoc(doc);     return 0;}int UpdateXml(const char* path,map<string,string>& keyValue){/* Init libxml */         xmlInitParser();int res  = _UpdateXml(path,keyValue);xmlCleanupParser();return res;}int main(int argc, char *argv[]){printf("Hello, world\n");map<string,string> m;m["/doc/parent/discarded/@info"] = string("info attri");m["/doc/parent/discarded[2]"] = string("change second discarded text 中文");int ret = UpdateXml("xpath2.res",m);assert(!ret);ret = UpdateXml("xpath2.res",m);assert(!ret);ret = UpdateXml("xpath2.res",m);assert(!ret);return 0;}

文件3: xpath2.res

<?xml version="1.0" encoding="UTF-8"?><doc>  <parent>    <discarded info="test">discarded</discarded>    <preserved/>    This text node must be discarded    <discarded>test</discarded>    <preserved>      content1      <child1/>      <child2>content2</child2>      <preserved>too</preserved>      <child2>content3</child2>      <preserved/>      <child2>content4</child2>      <preserved/>      <child2>content5</child2>      content6    </preserved>  </parent></doc>

文件4：修改后的 xpath2.res

<?xml version="1.0" encoding="UTF-8"?><doc>  <parent>    <discarded info="info attri">discarded</discarded>    <preserved/>    This text node must be discarded    <discarded>change second discarded text 中文</discarded>    <preserved>      content1      <child1/>      <child2>content2</child2>      <preserved>too</preserved>      <child2>content3</child2>      <preserved/>      <child2>content4</child2>      <preserved/>      <child2>content5</child2>      content6    </preserved>  </parent></doc>