jsoncpp的api简要说明

1  jsoncpp的api简要说明

1,解析(json字符串转为对象)

std::string strDataJson;

Json::Reader JReader; 

Json::Value JObject;

if (!JReader.parse(strDataJson, JObject))

{

cerr << "parse json error." << endl;

return bSuccess;

}

2,读取

std::string strMsg = JRec["msg"].asString();

int nRetCode = JRec["ret"]..asInt();

Json::Value JList = JRec["data"]["list"];

int nSize = JList.size();

获取错误信息： JReader.getFormatedErrorMessages()

3,增加或修改

JRoot["stringdata"] = Json::Value("msg");

JRoot["intdata"] = Json::Value(10);

4,删除

JValue.removeMember("toberemove");

5,对象转为字符串

//输出无格式json字符串

Json::FastWriter fast_writer;

strJRecList = fast_writer.write(JRoot);

//格式化之后的json,有回车换行符

std::string strOut = JRoot.toStyledString(）；

转自;http://my.oschina.net/chenleijava/blog/144312

6各种json子类型的使用

(1)json Object 

 for (Json::ValueIterator iter=groups_config.begin(); iter!=groups_config.end();iter++) {
      Json::Value client_dict = (*iter)["clients"];
      string topic_recresult = (*iter)["topics"]["recresult"].asString();
      string topic_recreq = (*iter)["topics"]["recreq"].asString();
      string topic_input = (*iter)["topics"]["input"].asString();
      for (Json::ValueIterator client_iter=client_dict.begin(); client_iter != client_dict.end(); ++client_iter) {
        string cid = client_iter.key().asString();
        // FIXME: create a new customer configuration
        CustomerPtr c(new Customer);
        c->LoadFromJson(cid, (*client_iter), topic_recresult, topic_recreq, topic_input);
        customers[cid] = c;
      }
    }

2 详细API

 </pre><pre code_snippet_id="342950" snippet_file_name="blog_20140513_1_8471295" name="code" class="cpp">class JSONAPI_API JsonValue
     {
         typedef std::map<std::string, JsonValue*> InnerMap;
         typedef std::vector<JsonValue*>               InnerVector;

     public:
         JsonValue();
         virtual ~JsonValue();

     public:
         void clear();

         //import/export
         void parse(const char* jsonString);
         JsonString toString();
         JsonString toString_styled();
         void toFile(const char* filename);
         void toFile_styled(const char* filename);

         //set
         void operator=(JsonValue& jval);

         void operator=(char vInteger);
         void operator=(unsigned char vInteger);
         void operator=(short vInteger);
         void operator=(unsigned short vInteger);
         void operator=(long vInteger);
         void operator=(unsigned long vInteger);
         void operator=(int vInteger);
         void operator=(unsigned int vInteger);
         void operator=(__int64 vInteger);
         void operator=(unsigned __int64 vInteger);
         void operator=(float vReal);
         void operator=(double vReal);
         void operator=(bool vBoolean);
         void operator=(const char* vString);

         int append(JsonValue& jval);
         int append(char vInteger);
         int append(unsigned char vInteger);
         int append(short vInteger);
         int append(unsigned short vInteger);
         int append(long vInteger);
         int append(unsigned long vInteger);
         int append(int vInteger);
         int append(unsigned int vInteger);
         int append(__int64 vInteger);
         int append(unsigned __int64 vInteger);
         int append(float vReal);
         int append(double vReal);
         int append(bool vBoolean);
         int append(const char* vString);

         //get
         JsonValue& operator [](const char* name);
         JsonValue& operator [](unsigned int arrIdx0);

         //get final value
         char            getChar();
         unsigned char   getUChar();
         short           getShort();
         unsigned short  getUShort();
         long            getLong();
         unsigned long   getULong();
         int             getInt();
         unsigned int    getUInt();
         __int64         getInt64();
         unsigned __int64 getUInt64();
         bool            getBoolean();
         float           getFloat();
         double          getDouble();
         const char*     getString();

         //check
         bool isNull();
         bool isChar();
         bool isUChar();
         bool isShort();
         bool isUShort();
         bool isLong();
         bool isULong();
         bool isInt();
         bool isUInt();
         bool isInt64();
         bool isUInt64();
         bool isBoolean();
         bool isFloat();
         bool isDouble();
         bool isString();
         bool isObject();
         bool isArray();

     protected:
         ValueType m_valueType;
         union
         {
             __int64 m_integer;
             double m_real;
             bool m_boolean;
             char* m_string;
             InnerMap* m_kv;
             InnerVector* m_array;
         }m_v;

     protected:
         void setAsObject();
         void setAsArray();

         friend JValHelper;
     };

1.jsoncpp是什么？

jsoncpp是一个使用C++语言来解析json文件的开源库，其项目地址为：http://sourceforge.net/projects/jsoncpp/，属于免费项目，任何人都可以下载使用

2. 编译jsoncpp

jsoncpp文件中提供了vs71的工程文件以及makerelease.py文件，用来编译，里面分为jsontest、lib_json、test_lib_json三个工程，按照自己需要的编译。

注意:如果使用VS默认的编译选项MTd或者MT，在使用json_libmtd.lib的时候可能会出现LNK2038错误(我使用的VS2012 vc110环境)，所以请修改MTD为MDd，MT为MD。

3.使用jsoncpp读JSON文件

如何将lib库添加进VS工程中在此就不赘述了。先看第一个读文件的例

 // JSON文件
 {"address":[
     {"name":"eliteYang", "email":"[email protected]"},
     {"name":"AAA", "email":"[email protected]"},
     {"name":"BBB", "email":"[email protected]"}
 ]}

 /**
  * file     :   jsoncpp_test.cpp
  * author   :   eliteYang
  * email    :   [email protected]
  * blog     :   http://www.cppfasn.org
  * desc     :   json cpp test
  */

 #include <fstream>
 #include <string>
 #include "jsoncpp/json.h"

 int _tmain(int argc, _TCHAR* argv[])
 {
     std::ifstream ifs;
     ifs.open("test.json");

     Json::Reader reader;
     Json::Value root;
     if (!reader.parse(ifs, root, false))
     { return -1; }

     Json::Value add_value = root["address"];
     for (int i = 0; i < add_value.size(); ++i)
     {
         Json::Value temp_value = add_value[i];
         std::string strName = temp_value["name"].asString();
         std::string strMail = temp_value["email"].asString();
         std::cout << "name: " << strName << " email: " << strMail << std::endl;

         // use value array[index]
         //Json::Value temp_value = add_value[i];
         //std::string strName = add_value[i]["name"].asString();
         //std::string strMail = add_value[i]["email"].asString();
         //std::cout << "name: " << strName << " email: " << strMail << std::endl;
     }

     system("Pause");

     return 0;
 }

结果：

name: eliteYang email: [email protected]
name: AAA email: [email protected]
name: BBB email: [email protected]
请按任意键继续. . .

跟我们文件中的数据完全一致。

4.使用JSON写入一块数据

我们继续使用上述文件，在中间加上一块数据。我们插入一个新的{"name": "append", "email": "[email protected]"}

 /**
  * file     :   jsoncpp_test.cpp
  * author   :   eliteYang
  * email    :   [email protected]
  * blog     :   http://www.cppfasn.org
  * desc     :   json cpp test
  */

 #include <fstream>
 #include <string>
 #include "jsoncpp/json.h"

 int _tmain(int argc, _TCHAR* argv[])
 {
     std::ifstream ifs;
     ifs.open("test.json");

     Json::Reader reader;
     Json::Value root;
     if (!reader.parse(ifs, root, false))
     { return -1; }

     Json::Value& add_value = root["address"];
     Json::Value append_value;
     append_value["name"] = "append";
     append_value["email"] = "[email protected]";
     add_value.append(append_value);

     for (int i = 0; i < add_value.size(); ++i)
     {
         Json::Value temp_value = add_value[i];
         std::string strName = temp_value["name"].asString();
         std::string strMail = temp_value["email"].asString();
         std::cout << "name: " << strName << " email: " << strMail << std::endl;
     }

     Json::FastWriter writer;
     std::string json_append_file = writer.write(root);

     std::ofstream ofs;
     ofs.open("test_append.json");
     ofs << json_append_file;

     system("Pause");

     return 0;
 }

结果：

name: eliteYang email: [email protected]
name: AAA email: [email protected]
name: BBB email: [email protected]
name: append email: [email protected]
请按任意键继续. . .

 // test_append.json
 {"address":[{"email":"[email protected]","name":"eliteYang"},{"email":"[email protected]","name":"AAA"},{"email":"[email protected]","name":"BBB"},{"email":"[email protected]","name":"append"}]}

转自：http://www.cppfans.org/1445.html

一个jsoncpp的例子

使用jsoncpp进行字符串、数字、布尔值和数组的封装与解析。

1）下载jsoncpp的代码库 百度网盘地址 ：http://pan.baidu.com/s/1ntqQhIT

2）解压缩文件 jsoncpp.rar

unzip jsoncpp.rar

3）修改jsoncpp/src/main.cpp文件

vim src/main.cpp

  1 #include <string>
  2 #include <json/json.h>
  3 #include "stdio.h"
  4 
  5 int ReadJson(const std::string &);
  6 std::string writeJson();
  7 
  8 int main(int argc, char** argv)
  9 {
 10     using namespace std;
 11 
 12     std::string strMsg;
 13 
 14     cout<<"--------------------------------"<<endl;
 15     strMsg = writeJson();
 16     cout<< "json write : " << endl << strMsg << endl;
 17     cout<<"--------------------------------"<<endl;
 18     cout<< "json read :" << endl;
 19     ReadJson(strMsg);
 20     cout<<"--------------------------------"<<endl;
 21 
 22     return 0;
 23 }
 24 
 25 int ReadJson(const std::string & strValue) 
 26 {
 27     using namespace std;
 28 
 29     Json::Reader reader;
 30     Json::Value value;
 31 
 32     if (reader.parse(strValue, value))
 33     {
 34         //解析json中的对象
 35         string out = value["name"].asString();
 36         cout << "name : "   << out << endl;
 37         cout << "number : " << value["number"].asInt() << endl;
 38         cout << "value : "  << value["value"].asBool() << endl;
 39         cout << "no such num : " << value["haha"].asInt() << endl;
 40         cout << "no such str : " << value["hehe"].asString() << endl;
 41 
 42         //解析数组对象
 43         const Json::Value arrayNum = value["arrnum"];
 44         for (unsigned int i = 0; i < arrayNum.size(); i++)
 45         {
 46             cout << "arrnum[" << i << "] = " << arrayNum[i];
 47         }
 48         //解析对象数组对象
 49         Json::Value arrayObj = value["array"];
 50         cout << "array size = " << arrayObj.size() << endl;
 51         for(unsigned int i = 0; i < arrayObj.size(); i++)
 52         {
 53             cout << arrayObj[i];
 54         }
 55         //从对象数组中找到想要的对象
 56         for(unsigned int i = 0; i < arrayObj.size(); i++)
 57         {
 58             if (arrayObj[i].isMember("string")) 
 59             {
 60                 out = arrayObj[i]["string"].asString();
 61                 std::cout << "string : " << out << std::endl;
 62             }
 63         }
 64     }
 65 
 66     return 0;
 67 }
 68 
 69 std::string writeJson() 
 70 {
 71     using namespace std;
 72 
 73     Json::Value root;
 74     Json::Value arrayObj;
 75     Json::Value item;
 76     Json::Value iNum;
 77 
 78     item["string"]    = "this is a string";
 79     item["number"]    = 999;
 80     item["aaaaaa"]    = "bbbbbb";
 81     arrayObj.append(item);
 82 
 83     //直接对jsoncpp对象以数字索引作为下标进行赋值，则自动作为数组
 84     iNum[1] = 1;
 85     iNum[2] = 2;
 86     iNum[3] = 3;
 87     iNum[4] = 4;
 88     iNum[5] = 5;
 89     iNum[6] = 6;
 90 
 91     //增加对象数组
 92     root["array"]    = arrayObj;
 93     //增加字符串
 94     root["name"]    = "json";
 95     //增加数字
 96     root["number"]    = 666;
 97     //增加布尔变量
 98     root["value"]    = true;
 99     //增加数字数组
100     root["arrnum"]    = iNum;
101 
102     root.toStyledString();
103     string out = root.toStyledString();
104 
105     return out;
106 }

4）在目录jsoncpp/ 下执行make命令

jsoncpp$ make
mkdir -p objs/src/json;  mkdir -p objs/src;
g++ -c -Wall -Werror -g -I include src/json/json_reader.cpp -o objs/src/json/json_reader.o
g++ -c -Wall -Werror -g -I include src/json/json_value.cpp -o objs/src/json/json_value.o
g++ -c -Wall -Werror -g -I include src/json/json_writer.cpp -o objs/src/json/json_writer.o
g++ -c -Wall -Werror -g -I include src/main.cpp -o objs/src/main.o
g++  objs/src/json/json_reader.o objs/src/json/json_value.o objs/src/json/json_writer.o objs/src/main.o -o main

5)运行jsoncpp/下的main文件

./main

6)运行结果如下

fengbo: jsoncpp$ ./main 
--------------------------------
json write : 
{
   "array" : [
      {
         "aaaaaa" : "bbbbbb",
         "number" : 999,
         "string" : "this is a string"
      }
   ],
   "arrnum" : [ null, 1, 2, 3, 4, 5, 6 ],
   "name" : "json",
   "number" : 666,
   "value" : true
}

--------------------------------
json read :
name : json
number : 666
value : 1
no such num : 0
no such str : 
arrnum[0] = null
arrnum[1] = 1
arrnum[2] = 2
arrnum[3] = 3
arrnum[4] = 4
arrnum[5] = 5
arrnum[6] = 6
array size = 1

{
    "aaaaaa" : "bbbbbb",
    "number" : 999,
    "string" : "this is a string"
}
string : this is a string
--------------------------------