C++ jsoncpp解析json字符串

使用方法

下载源码解压之后得到jsoncpp-src-0.5.0文件夹，我们只需要jsoncpp的头文件和cpp文件，其中jsonscpp的头文件位于jsoncpp-src-0.5.0\include\json,jsoncpp的cpp文件位于jsoncpp-src-0.5.0\src\lib_json。

json: json操作所需的头文件，此文件夹名字不能修改，因为lib_json目录中所对应的.cpp里面包含头文件形式是这样：

#include <json/xxx.h>

lib_json：json操作所需的cpp文件，此文件夹名字可根据需要自行命名。

把json和lib_json拷贝出来放在你需要编写代码的目录中（注意：json 和 lib_json 要在同一级目录）：

从字符串中读取json

#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;

void readStrJson(); //从字符串中读取JSON
void readStrProJson(); //从字符串中读取JSON（内容复杂些）

int main(int argc, char *argv[])
{
readStrJson();

cout << "\n\n";
readStrProJson();

return 0;
}

//从字符串中读取JSON
void readStrJson()
{
//字符串
const char* str =
"{\"praenomen\":\"Gaius\",\"nomen\":\"Julius\",\"cognomen\":\"Caezar\","
"\"born\":-100,\"died\":-44}";

/*
//json内容如下：
{
"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;
}

}

//从字符串中读取JSON（内容复杂些）
void readStrProJson()
{
string strValue = "{\"name\":\"json\",\"array\":[{\"cpp\":\"jsoncpp\"},{\"java\":\"jsoninjava\"},{\"php\":\"support\"}]}";
/*
//json内容如下：
{
"name": "json″,
"array": [
{
"cpp": "jsoncpp"
},
{
"java": "jsoninjava"
},
{
"php": "support"
}
]
}
*/

Json::Reader reader;
Json::Value value;

if (reader.parse(strValue, value))
{
string out = value["name"].asString();
cout << out << endl;
const Json::Value arrayObj = value["array"];
for (unsigned int i = 0; i < arrayObj.size(); i++)
{
if (!arrayObj[i].isMember("cpp"))
continue;
out = arrayObj[i]["cpp"].asString();
cout << out;
if (i != (arrayObj.size() - 1))
cout << endl;
}
}
}

从文件中读取JSON

#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;

void readFileJson(); //从文件中读取JSON，一个存储了JSON格式字符串的文件

int main(int argc, char *argv[])
{
readFileJson();

return 0;
}

//从文件中读取JSON
void readFileJson()
{
Json::Reader reader;
Json::Value root;

//从文件中读取，保证当前文件有test.json文件
ifstream in("test.json", ios::binary);
//in.open("test.json", ios::binary);

if( !in.is_open() )
{
cout << "Error opening file\n";
return;
}

/*
//test.json内容如下：
{
"name":"Tsybius",
"age":23,
"sex_is_male":true,
"partner":
{
"partner_name":"Galatea",
"partner_age":21,
"partner_sex_is_male":false
},
"achievement":["ach1","ach2","ach3"]
}
*/

if(reader.parse(in,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(unsigned int i = 0; i < root["achievement"].size(); i++)
{
string ach = root["achievement"][i].asString();
cout << ach << '\t';
}
cout << endl;

cout << "Reading Complete!" << endl;
}
else
{
cout << "parse error\n" << endl;
}

in.close();
}

test.json文件内容如下:
{
"name":"Mike Jiang",
"age":23,
"sex_is_male":true,
"partner":
{
"partner_name":"Galatea",
"partner_age":21,
"partner_sex_is_male":false
},
"achievement":["ach1","ach2","ach3"]
}

把信息保存为JSON格式

#include <string>
#include <json/json.h>
#include <iostream>
#include <fstream>
using namespace std;

void writeFileJson();//将信息保存为JSON格式

int main(int argc, char *argv[])
{
writeFileJson();

return 0;
}

//将信息保存为JSON格式
void writeFileJson()
{
//根节点
Json::Value root;

//根节点属性
root["name"] = Json::Value("Mike Jiang");
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("demo.json");
os << sw.write(root);
os.close();

/*
//json文件内容如下：
{
"achievement" : [ "ach1", "ach2", "ach3" ],
"age" : 23,
"name" : "Mike Jiang",
"partner" : {
"partner_age" : 21,
"partner_name" : "Galatea",
"partner_sex_is_male" : false
},
"sex_is_male" : true
}
*/

}