C++ jsoncpp解析json字符串

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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JSONvoid 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JSONvoid 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JSONvoid 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    }    */}

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