【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_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 <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_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 <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_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