Jsoncpp的安装与使用

在实际项目中，很多的启动文件，配置文件与数据传输格式都是使用json来进行的，好处不便多说。
1.安装
本人操作系统为ubuntu 16.04，直接运行下列语句就安装完毕。
将 /libjson_linux-gcc-5.4.0_libmt.* 放在 /lib/ 目录下。

sudo apt-get install libjsoncpp-dev

2.使用
**（1）先上要解析的json格式文件
其文件名为：json_text.txt

{"face":[{"attribute":{"age":27,"gender":"Male","lefteye_opendegree":43,"mouth_opendegree":2,"pose":{"raise":-21,"tilting":-2,"turn":4},"righteye_opendegree":47},"face_id":"83e3edac3d5d49579089d3ee043d41ec","position":{"center":{"x":179,"y":50},"eye_left":{"x":206,"y":78},"eye_right":{"x":248,"y":78},"height":94,"width":94},"tag":""}],"devices": [u'000_ce21',u'0000_ce22'],"img_height":500,"img_id":"030-3aff983ea4ea5a35f89ae6","img_width":350,"res_code":"0000","url":"http://e.hiphotos.baidu.com/baike/pic/item/9345d688d43f879428d347b3d81b0ef41bd53a7a.jpg"
}

（2）解析
“devices”: [u’000_ce21’,u’0000_ce22’]，此种格式在json 是认识的，因此我们先要对其进行处理，转换为：”devices”: [“000_ce21”,”0000_ce22”]。具体的解析代码如下：
命名为 jsoncpp_parse_test.cpp

#include <iostream>
#include <fstream>
#include "json/json.h"
using namespace std;
using namespace Json;string & replace_all(string& str,const string& old_value,const string& new_value)     {     while(true){     string::size_type   pos(0);     if((pos=str.find(old_value))!=string::npos)     str.replace(pos,old_value.length(),new_value);     else  break;     }     return  str;     }     int main()
{Json::Value root;  Json::Reader reader;string inputsStr,onelineStr;std::ifstream ifs;ifs.open("json_text.txt");while   (getline(ifs,onelineStr)){inputsStr+=onelineStr;}//cout<<inputsStr<<endl<<endl;inputsStr = replace_all(inputsStr,"u'","\""); inputsStr = replace_all(inputsStr,"'","\"");//cout<<inputsStr<<endl<<endl;if(!reader.parse(inputsStr, root)){  // fail to parse  cout << "img_width:\t"<<"error parse"<<endl;}  else{  // success  cout<<root["face"][0U]["face_id"];//string faceId = root["face"][0]["face_id"].asString();int imgWidth = (int)root["img_width"].asInt();int imgHeight = root["img_height"].asInt();string resCode = root["res_code"].asString();string url = root["url"].asString();//cout << "face_id:\t" << faceId << endl;cout << "img_width:\t" << imgWidth << endl;cout << "img_height:\t" << imgHeight << endl;cout << "res_code:\t" << resCode << endl;cout << "url:\t\t" << url << endl;unsigned int dev_size =  root["devices"].size();for (unsigned int i = 0; i < dev_size; ++i){cout<<"i:"<<i<<root["devices"][i]<<endl;}}  return 0;
}

基本思路：
将json中的内容加载到string 变量inputsStr中，在用reader.parse进行匹配是否符合json格式。在解析中数组的下标是unsigned int 类型，整数数在编译器中默认的是int类型，可以在其后面加U,比如0则为0U，否则会编译通过，运行segment error。

（3）编译脚本

#!/bin/sh
g++ jsoncpp_parse_test.cpp  -o test_cpp /lib/libjson_linux-gcc-5.4.0_libmt.so

（4）运行结果
Jsoncpp的安装与使用-编程之家

(5)有时 键值是不确定的，那如何解析呢？
json文件格式：

{"hunan":["cs","zz","xt"],"jiangxi":["nc","xy"]}

解析代码

#include <iostream>
#include <fstream>
#include "json/json.h"
using namespace std;
using namespace Json;int main()
{Value root;  Reader reader;string inputsStr,onelineStr;ifstream ifs;ifs.open("json_not_known_key.txt");while   (getline(ifs,onelineStr)){inputsStr+=onelineStr;}if(!reader.parse(inputsStr,root)){  // fail to parse  cout<<"  "<<"fail to parse,file not json type"<<endl;}  else{Json::Value::Members member = root.getMemberNames();for(Json::Value::Members::iterator iter = member.begin(); iter != member.end(); ++iter){string area = *iter;            unsigned int city_size = root[*iter].size();cout<<"city  "<<city_size<<endl;for (unsigned int iUid = 0; iUid < city_size; ++iUid){string city = root[*iter][iUid].asString();cout<<"area: "<<area<<"  city:  "<< city<<endl;             }}}
}

结果：
Jsoncpp的安装与使用-编程之家