【C++】JSON文件的读取和生成



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