C++程序有时候要读写XML文件， 这里介绍一个读写XML文件的库——Libxml2。

主页：http://xmlsoft.org/index.html

入门教程很详细的：http://jianlee.ylinux.org/Computer/C/libxml.html#sec11

读取节点内容的话用XPath方式比较好，要问XPath与Libxml2库之间的关系，有个很形象的比喻：

那就是SQL与数据库之间的关系。


下面的代码是在Linux下实现的：

#ifndef __XML_FILE_H__
#define __XML_FILE_H__

#include <stdio.h>
#include <stdlib.h>
#include <libxml/parser.h>
#include <libxml/tree.h>
#include <map>
#include <string>
#include <iostream>

using namespace std;

const int XML_READ = 1;
const int XML_WRITE = 0;

typedef struct _XML_INFO XML_INFO;
typedef struct _XML_INFO* HXML_INFO;

struct _XML_INFO
{
    char version[16];
    int update;
    int scan_speed;
    int type;
    int device_counts;
    int item_counts;
    
    map<string, string> map_item_info;
};

class CLibxml2
{
public:
    CLibxml2();
    ~CLibxml2();

    CLibxml2(const char *xml_file_path, bool is_read);

	/*!
	  \fn bool open(const char *xml_file_path, bool is_read)
	  \brief 打开一个XML文件是以读的方式还是以写的方式
	  \param in xml_file_path XML文件路径
	  \param in is_read true为读，false为写
	  \return true成功，false失败
	*/
    bool open(const char *xml_file_path, bool is_read);
    
	/*!
	  \fn bool parse_xml_file(XML_INFO &xml_info)
	  \brief 解析XML文件，将解析后的结果保存在XML_INFO结构体中
	  \param out xml_info 保存解析后的结果
	  \return true成功，false失败
	*/
    bool parse_xml_file(const XML_INFO &xml_info);

	/*!
	  \fn bool save_xml_file(const XML_INFO &xml_info)
	  \brief 写入XML文件
	  \param in xml_info 需要写入的信息
	  \return true成功，false失败
	*/
    bool save_xml_file(XML_INFO &xml_info);

private:
	/*!
	  \fn xmlNodePtr search_node_ptr(const char *sz_expr)
	  \brief 查找指定节点
	  \param in sz_expr 节点路径表达式（XPATH）
	  \return success返回指定节点指针，fail返回NULL
	*/
    xmlNodePtr search_node_ptr(const char *sz_expr);

private:
    char m_sz_path[512];
    xmlDocPtr m_pdoc_read;
    xmlNodePtr m_proot;
};


#endif // __XML_FILE_H__


#include "xml-file.h"
#include <string.h>
#include <libxml/xpath.h>
#include <libxml/xpathInternals.h>
#include <libxml/xmlmemory.h>
#include <libxml/xpointer.h>

CLibxml2::CLibxml2()
{
    m_pdoc_read = NULL;
    m_proot = NULL;
    bzero(m_sz_path, sizeof(m_sz_path));
}

CLibxml2::~CLibxml2()
{
    if (m_pdoc_read)
    {
        xmlFreeDoc(m_pdoc_read);
        m_pdoc_read = NULL;

        xmlCleanupParser();
        xmlMemoryDump();
    }
}

CLibxml2::CLibxml2(const char *xml_file_path, bool is_read)
{
    if (xml_file_path)
    {
        open(xml_file_path, is_read);
    }
}

bool CLibxml2::open(const char *xml_file_path, bool is_read)
{
    bool bret = false;
    
    m_pdoc_read = NULL;
    m_proot = NULL;
    bzero(m_sz_path, sizeof(m_sz_path));
    
    if (xml_file_path)
    {
        strcpy(m_sz_path, xml_file_path);

        if (is_read)
        {
            xmlKeepBlanksDefault(0);
            m_pdoc_read = xmlReadFile(xml_file_path, "UTF-8", XML_PARSE_RECOVER);
            m_proot = xmlDocGetRootElement(m_pdoc_read);
        }
        
        if (m_proot)
        {
            bret = true;
        }
    }

    return bret;
}

bool CLibxml2::parse_xml_file(XML_INFO &xml_info)
{
    bool bret = false;
    if (m_proot)
    {
        xmlNodePtr node = search_node_ptr("//config_Information");
        xmlChar *str = xmlGetProp(node, node->properties->name);
        strcpy(xml_info.version, (const char*)BAD_CAST(str));
        //cout << xml_info.version << endl;

        node = search_node_ptr("//Config_Data_block");
        str = xmlGetProp(node, node->properties->name);
        xml_info.update = atoi((const char*)BAD_CAST(str));
        //cout << xml_info.update << endl;

        node = search_node_ptr("//ScanSpeed");
        str = xmlNodeGetContent(node);
        xml_info.scan_speed = atoi((const char*)BAD_CAST(str));
        //cout << xml_info.scan_speed << endl;

        node = search_node_ptr("//DeviceType");
        str = xmlGetProp(node, node->properties->name);
        xml_info.type = atoi((const char*)BAD_CAST(str));
        //cout << xml_info.type << endl;

        node = search_node_ptr("//Device_Counts");
        str = xmlNodeGetContent(node);
        xml_info.device_counts = atoi((const char*)BAD_CAST(str));
        //cout << xml_info.device_counts << endl;

        node = search_node_ptr("//Item_Counts");
        str = xmlNodeGetContent(node);
        xml_info.item_counts = atoi((const char*)BAD_CAST(str));
        //cout << xml_info.item_counts << endl;

        int i;
        char item_id[32];
        char key_word[32];
        char id_content[32];
        char key_content[32];
        xmlNodePtr node_id;
        xmlNodePtr node_key;
        
        for (i=1; i<=xml_info.item_counts; i++)
        {
            bzero(item_id, sizeof(item_id));
            bzero(key_word, sizeof(key_word));
            bzero(id_content, sizeof(id_content));
            bzero(key_content, sizeof(key_content));
            
            sprintf(item_id, "//ItemInfo[%d]/ItemID", i);
            sprintf(key_word, "//ItemInfo[%d]/KeyWord", i);
            node_id = search_node_ptr(item_id);
            node_key = search_node_ptr(key_word);
            xmlChar *temp_id = xmlNodeGetContent(node_id);
            xmlChar *temp_key = xmlNodeGetContent(node_key);
            strcpy(id_content, (const char*)BAD_CAST(temp_id));
            strcpy(key_content, (const char*)BAD_CAST(temp_key));
            xml_info.map_item_info.insert(pair<string, string>(id_content, key_content));
        }
        
        bret = true;
    }

    return bret;
}

bool CLibxml2::save_xml_file(const XML_INFO &xml_info)
{
    if (NULL == m_sz_path)
    {
        return false;
    }

    char sz_temp[32];
    
    xmlDocPtr pdoc = xmlNewDoc(BAD_CAST(xml_info.version));
    xmlNodePtr config_info = xmlNewNode(NULL, BAD_CAST"config_Information");
    xmlNewProp(config_info, BAD_CAST"version", BAD_CAST(xml_info.version));
    xmlDocSetRootElement(pdoc, config_info);
    
    xmlNodePtr data_block = xmlNewNode(NULL, BAD_CAST"Config_Data_block");
    bzero(sz_temp, sizeof(sz_temp));
    sprintf(sz_temp, "%d", xml_info.update);
    xmlNewProp(data_block, BAD_CAST"update", BAD_CAST(sz_temp));
    xmlAddChild(config_info, data_block);

    bzero(sz_temp, sizeof(sz_temp));
    sprintf(sz_temp, "%d", xml_info.scan_speed);
    xmlNewTextChild(data_block, NULL, BAD_CAST"ScanSpeed", BAD_CAST(sz_temp));

    bzero(sz_temp, sizeof(sz_temp));
    sprintf(sz_temp, "%d", xml_info.type);
    xmlNodePtr device_type = xmlNewNode(NULL, BAD_CAST"DeviceType");
    xmlNewProp(device_type, BAD_CAST"type", BAD_CAST(sz_temp));
    xmlAddChild(data_block, device_type);

    bzero(sz_temp, sizeof(sz_temp));
    sprintf(sz_temp, "%d", xml_info.item_counts);
    xmlNewTextChild(device_type, NULL, BAD_CAST"Item_Counts", BAD_CAST(sz_temp));
    int index = 1;
    int ncounts = xml_info.item_counts;
    
    xmlNodePtr item_list = xmlNewNode(NULL, BAD_CAST"Item_list");
    xmlAddChild(device_type, item_list);

    map<string, string>::iterator iter;
    for (iter=xml_info.map_item_info.begin();
         iter!=xml_info.map_item_info.end();
         ++iter)
    {
        
        bzero(sz_temp, sizeof(sz_temp));
        sprintf(sz_temp, "%d", index++);
        xmlNodePtr item_info = xmlNewNode(NULL, BAD_CAST"ItemInfo");
        xmlNewProp(item_info, BAD_CAST"NO", BAD_CAST(sz_temp));
        xmlAddChild(item_list, item_info);

        xmlNewTextChild(item_info, NULL, BAD_CAST"ItemID",
                        BAD_CAST((*iter).first.c_str()));
        xmlNewTextChild(item_info, NULL, BAD_CAST"KeyWord",
                        BAD_CAST((*iter).second.c_str()));
    }
    
    xmlSaveFormatFileEnc(m_sz_path, pdoc, "UTF-8", 1);
    xmlFreeDoc(pdoc);
    return true;
}

xmlNodePtr CLibxml2::search_node_ptr(const char *sz_expr)
{
    xmlNodePtr node_ret;
    
    if (sz_expr == NULL)
    {
        return NULL;
    }
    
    xmlChar *sz_path = BAD_CAST(sz_expr);
    xmlXPathContextPtr context = xmlXPathNewContext(m_pdoc_read);
    xmlXPathObjectPtr result = xmlXPathEvalExpression(sz_path, context);
    
    if (result == NULL)
    {
        return NULL;
    }
    if (xmlXPathNodeSetIsEmpty(result->nodesetval))
    {
        return NULL;
    }

    xmlXPathFreeContext(context);
    
    node_ret = xmlXPtrBuildNodeList(result);

    return node_ret;
}

/*/测试//
int main(void)
{
    //write/
    CLibxml2 lib("rmc1.xml", XML_WRITE);

    map<string, string> map_item;
    XML_INFO xml_info;
    xml_info.map_item_info.insert(pair<string, string>("CPU", ""));
    xml_info.map_item_info.insert(pair<string, string>("MEM", ""));
    xml_info.map_item_info.insert(pair<string, string>("DISK_C_FREE", "C"));
    xml_info.map_item_info.insert(pair<string, string>("RunTime", ""));
    xml_info.map_item_info.insert(pair<string, string>("MainProcess0", "test.exe"));
    xml_info.map_item_info.insert(pair<string, string>("NetPing", "127.0.0.1"));
    
    strcpy(xml_info.version, "1.0");
    xml_info.update = 0;
    xml_info.scan_speed = 100;
    xml_info.type = 2;
    xml_info.device_counts = 2;
    xml_info.item_counts = xml_info.map_item_info.size();

    lib.save_xml_file(xml_info);
    //


    //read/
    XML_INFO xml_info;
    CLibxml2 lib("rmc.xml", XML_READ);
    lib.parse_xml_file(xml_info);

    map<string, string>::iterator iter;
    for (iter = xml_info.map_item_info.begin();
         iter != xml_info.map_item_info.end();
         ++iter)
    {
        cout << (*iter).first << endl;
        cout << (*iter).second << endl;
    }
    

   
    return 0;
}
//*


<?xml version="1.0"?>
<config_Information version="1.0">
<Config_Data_block update="0">
<ScanSpeed>100</ScanSpeed>
<DeviceType type="2">
<Device_Counts>1</Device_Counts>
<Item_Counts>6</Item_Counts>
<Item_list>
<ItemInfo NO="1">
	<ItemEvenFlag>1</ItemEvenFlag>
	<ItemID>CPU</ItemID>
	<KeyWord></KeyWord>
</ItemInfo>
<ItemInfo NO="2">
	<ItemID>MEM</ItemID>
	<KeyWord></KeyWord>
</ItemInfo>
<ItemInfo NO="3">
	<ItemID>DISK_C_FREE</ItemID>
	<KeyWord>C</KeyWord>
</ItemInfo>
<ItemInfo NO="4">
	<ItemID>RunTime</ItemID>
	<KeyWord></KeyWord>
</ItemInfo>
<ItemInfo NO="5">
	<ItemID>MainProcess0</ItemID>
	<KeyWord>test.exe</KeyWord>
</ItemInfo>
<ItemInfo NO="6">
	<ItemID>NetPing</ItemID>
	<KeyWord>127.0.0.1</KeyWord>
</ItemInfo>
</Item_list>
</DeviceType>
</Config_Data_block>
</config_Information>


# xml # c++
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