json读取和写入数据

一、从字符串中读取JSON

a.cpp

#include

#include "json/json.h"

using  namespace  std;

int  main()
{
    //字符串
    const  char * str =
        "{\"praenomen\":\"Gaius\",\"nomen\":\"Julius\",\"cognomen\":\"Caezar\","
        "\"born\":-100,\"died\":-44}" ;

    Json::Reader reader;
    Json::Value root;

    //从字符串中读取数据
    if (reader.parse(str,root))
    {
        string praenomen = root[ "praenomen" ].asString();
        string nomen = root[ "nomen" ].asString();
        string cognomen = root[ "cognomen" ].asString();
        int  born = root[ "born" ].asInt();
        int  died = root[ "died" ].asInt();

        cout << praenomen +  " "  + nomen +  " "  + cognomen
            <<  " was born in year "  << born
            <<  ", died in year "  << died << endl;
    }

    return  0;
}

makefile文件

LIB=-L /usr/local/lib/libjson/  -ljson_linux- gcc -4.4.7_libmt

a: a.o
    g++ -o a -std=c++0x a.o $(LIB)
a.o: a.cpp
    g++ -c a.cpp
clean:
    rm  -rf a.o a

运行结果

二、从文件中读取JSON

PersonalInfo.json（一个存储了JSON格式字符串的文件）

{
    "name" : "Tsybius" ,
    "age" :23,
    "sex_is_male" : true ,
    "partner" :
    {
        "partner_name" : "Galatea" ,
        "partner_age" :21,
        "partner_sex_is_male" : false
    },
    "achievement" :[ "ach1" , "ach2" , "ach3" ]
}

a.cpp

#include
#include

#include "json/json.h"

using  namespace  std;

int  main()
{
    Json::Reader reader;
    Json::Value root;

    //从文件中读取
    ifstream is;
    is.open( "PersonalInfo.json" , ios::binary);

    if (reader.parse(is,root))
    {
        //读取根节点信息
        string name = root[ "name" ].asString();
        int  age = root[ "age" ].asInt();
        bool  sex_is_male = root[ "sex_is_male" ].asBool();

        cout <<  "My name is "  << name << endl;
        cout <<  "I'm "  << age <<  " years old"  << endl;
        cout <<  "I'm a "  << (sex_is_male ?  "man"  :  "woman" ) << endl;

        //读取子节点信息
        string partner_name = root[ "partner" ][ "partner_name" ].asString();
        int  partner_age = root[ "partner" ][ "partner_age" ].asInt();
        bool  partner_sex_is_male = root[ "partner" ][ "partner_sex_is_male" ].asBool();

        cout <<  "My partner's name is "  << partner_name << endl;
        cout << (partner_sex_is_male ?  "he"  :  "she" ) <<  " is "
            << partner_age <<  " years old"  << endl;

        //读取数组信息
        cout <<  "Here's my achievements:"  << endl;
        for ( int  i = 0; i < root[ "achievement" ].size(); i++)
        {
            string ach = root[ "achievement" ][i].asString();
            cout << ach <<  '\t' ;
        }
        cout << endl;

        cout <<  "Reading Complete!"  << endl;
    }

    is.close();

    return  0;
}

makefile

LIB=-L /usr/local/lib/libjson/  -ljson_linux- gcc -4.4.7_libmt

a: a.o
    g++ -o a -std=c++0x a.o $(LIB)
a.o: a.cpp
    g++ -c a.cpp
clean:
    rm  -rf a.o a

运行结果

三、将信息保存为JSON格式

a.cpp

#include
#include

#include "json/json.h"

using  namespace  std;

int  main()
{
    //根节点
    Json::Value root;

    //根节点属性
    root[ "name" ] = Json::Value( "Tsybius" );
    root[ "age" ] = Json::Value(23);
    root[ "sex_is_male" ] = Json::Value( true );

    //子节点
    Json::Value partner;

    //子节点属性
    partner[ "partner_name" ] = Json::Value( "Galatea" );
    partner[ "partner_age" ] = Json::Value(21);
    partner[ "partner_sex_is_male" ] = Json::Value( false );

    //子节点挂到根节点上
    root[ "partner" ] = Json::Value(partner);

    //数组形式
    root[ "achievement" ].append( "ach1" );
    root[ "achievement" ].append( "ach2" );
    root[ "achievement" ].append( "ach3" );

    //直接输出
    cout <<  "FastWriter:"  << endl;
    Json::FastWriter fw;
    cout << fw.write(root) << endl << endl;

    //缩进输出
    cout <<  "StyledWriter:"  << endl;
    Json::StyledWriter sw;
    cout << sw.write(root) << endl << endl;

    //输出到文件
    ofstream os;
    os.open( "PersonalInfo" );
    os << sw.write(root);
    os.close();

    return  0;
}

makefile

LIB=-L /usr/local/lib/libjson/  -ljson_linux- gcc -4.4.7_libmt

a: a.o
    g++ -o a -std=c++0x a.o $(LIB)
a.o: a.cpp
    g++ -c a.cpp
clean:
    rm  -rf a.o a

运行结果

生成的文件PersonalInfo.json

{
   "achievement"  : [  "ach1" ,  "ach2" ,  "ach3"  ],
   "age"  : 23,
   "name"  :  "Tsybius" ,
   "partner"  : {
      "partner_age"  : 21,
      "partner_name"  :  "Galatea" ,
      "partner_sex_is_male"  :  false
   },
   "sex_is_male"  :  true
}

END