【C++】JSON文件的读取和生成



一、从字符串中读取JSON

a.cpp

#include <iostream>#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_libmta: a.o    g++ -o a -std=c++0x a.o $(LIB)a.o: a.cpp     g++ -c a.cppclean:    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 <iostream>#include <fstream>#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_libmta: a.o    g++ -o a -std=c++0x a.o $(LIB)a.o: a.cpp     g++ -c a.cppclean:    rm -rf a.o a

运行结果

三、将信息保存为JSON格式

a.cpp

#include <iostream>#include <fstream>#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_libmta: a.o    g++ -o a -std=c++0x a.o $(LIB)a.o: a.cpp     g++ -c a.cppclean:    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}

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