C、C++中对json格式数据的解析和封装

中对json格式数据的解析和封装"/>

C、C++中对json格式数据的解析和封装

C:首先需要调库：#include <cJSON.h>

Json的数据结构介绍：
/* The cJSON structure: */
typedef struct cJSON
{
/*next/prev允许您遍历数组/对象链。或者，使用GetArraySize/GetArrayItem/GetObjectItem */
struct cJSON *next;
struct cJSON *prev;
/* 数组或对象项将有一个子指针指向数组/对象中的项链。 */
struct cJSON *child;/* 项目的类型，如上所述。*/
int type;/* 字符串, if type==cJSON_String */
char *valuestring;
/* 数值, if type==cJSON_Number */
int valueint;
/* 小数数据, if type==cJSON_Number */
double valuedouble;/* 项的名称字符串，如果此项是的子项，或在对象的子项列表中。*/
char *string;
} cJSON;

Json格式文本解析：
#define TEST2 "{\n\"auth\": \"auc_d0dd49997dd17b12f76b74fe51d0de3fd772718b\",\n\"sessionId\": \"5129110798518519880764729435382\"\n}"
char* buffer = TEST2;
cJSON* json = cJSON_Parse(buffer);
cJSON* name = cJSON_GetObjectItem(json, "name");
cJSON* num = cJSON_GetObjectItem(json, "num");
printf("%s,%s",name->valuestring,num->valueint);假设文本为：需要解析中间的pinyin,textContent,title
"Data":{"listItems":[{"htmlView":"=一飞冲天&ptype=zici","mediaId":"6f7af22ba4613b869f455d569c204c69","selfData":"{\"interpretation\":\"鸟儿展翅一飞，直冲云霄。比喻平时没有特殊表现，一下做出了惊人的成绩。\",\"lemma\":\"一飞冲天\",\"pinyin\":\"[yī fēi chōng tiān]\"}\n","textContent":"鸟儿展翅一飞，直冲云霄。比喻平时没有特殊表现，一下做出了惊人的成绩。","title":"一飞冲天"}]}cJSON* Data = cJSON_GetObjectItem(json, "Data");
cJSON* ListItems = cJSON_GetObjectItem(Data, "listItems");
cJSON* Json_Array = cJSON_GetArrayItem(ListItems, 0);//其中[]里面为数组需要用cJSON_GetArrayItem，0代表第一个。
cJSON* TextContent = cJSON_GetObjectItem(Json_Array, "textContent");
cJSON* Title = cJSON_GetObjectItem(Json_Array, "title");
cJSON* SelfData = cJSON_GetObjectItem(Json_Array, "selfData");
cJSON* Src = cJSON_Parse(SelfData->valuestring);//selfData数据解析出来为字符串，需要再次解析为json数据才能再次解析
cJSON* Pinyin = cJSON_GetObjectItem(Src, "pinyin");

Json格式文本封装：将多条字符串合成一条json格式数据
const char* client_id = "12345678";
const char* sessionid = "abcdefg";
cJSON *root = cJSON_CreateObject();
cJSON_AddStringToObject(root, "authCode", client_id);
cJSON_AddStringToObject(root, "sessionId", sessionid);//这里的添加处理字符串以外还可以添加很多类型的数据
char *auth_resp_info = cJSON_Print(root);
printf("%s,%s",auth_resp_info);

C++封装json格式数据:

创建一个C++类来封装这个JSON数据：

#include <iostream>
#include <string>
#include <vector>class Address {
public:std::string street;std::string city;
};class Person {
public:std::string name;int age;Address address;std::vector<std::string> hobbies;
};int main() {Person person;person.name = "John";person.age = 30;person.address.street = "123 Main St";person.address.city = "New York";person.hobbies = {"Reading", "Hiking"};// 将Person对象转换为JSON字符串nlohmann::json j;j["person"]["name"] = person.name;j["person"]["age"] = person.age;j["person"]["address"]["street"] = person.address.street;j["person"]["address"]["city"] = person.address.city;j["person"]["hobbies"] = person.hobbies;std::string jsonStr = j.dump();std::cout << jsonStr << std::endl;return 0;
}

 最后的数据为：

{"person": {"name": "John","age": 30,"address": {"street": "123 Main St","city": "New York"},"hobbies": ["Reading", "Hiking"]}
}

还有些栗子： 

json json_data;
json_data["Header"] = {{"DSN","5ca439320d7b4adfb965a4442c791c33"}};
json_data["Payload"] = {{"blobData",{{"longitude",""},{"latitude",""}}},{"domain","weather"},{"intent","GetGeneralMsgRequest"}};最后形成：JSON string: {"Header": {"DSN": "5ca439320d7b4adfb965a4442c791c33"},"Payload": {"blobData": {"latitude": "","longitude": ""},"domain": "weather","intent": "GetGeneralMsgRequest"}}或者可以这样：也可以形成上面的数据
json j2 = R"("Header": {"DSN": "5ca439320d7b4adfb965a4442c791c33"},"Payload": {"blobData": {"latitude": "","longitude": ""},"domain": "weather","intent": "GetGeneralMsgRequest"}
)"_json;

要想打印上面封装的json的数据可以用以字符串的形式：json_data.dump(4)

C++解析json格式数据: 

1、RapidJSON：RapidJSON是一个非常快速的JSON解析库，它提供了简单的API来解析和生成JSON数据。

示例代码：

#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include <iostream>
#include <string>int main() {const char* json = "{\"name\":\"John\",\"age\":30,\"city\":\"New York\"}";rapidjson::Document doc;doc.Parse(json);if (!doc.HasParseError()) {std::string name = doc["name"].GetString();int age = doc["age"].GetInt();std::string city = doc["city"].GetString();std::cout << "Name: " << name << ", Age: " << age << ", City: " << city << std::endl;} else {std::cout << "JSON parse error" << std::endl;}return 0;
}

 2、JSON for Modern C++ (nlohmann/json)：这是一个现代C++中使用的非常流行的JSON解析库。它提供了简单的API和STL兼容性，容易学习和使用。

示例代码：

#include <nlohmann/json.hpp>
#include <iostream>
#include <string>int main() {std::string json = "{\"name\":\"John\",\"age\":30,\"city\":\"New York\"}";nlohmann::json j = nlohmann::json::parse(json);std::string name = j["name"];int age = j["age"];std::string city = j["city"];std::cout << "Name: " << name << ", Age: " << age << ", City: " << city << std::endl;return 0;
}

C++中解析多重json格式的数据：

在C++中获取多重JSON格式的数据，你需要逐级解析JSON结构，以访问嵌套在JSON对象或数组中的数据。以下是一个示例，演示如何处理多重嵌套的JSON数据。

假设你有以下JSON数据：

{"person": {"name": "John","age": 30,"address": {"street": "123 Main St","city": "New York"},"hobbies": ["Reading", "Hiking"]}
}

你可以使用RapidJSON或nlohmann/json等JSON解析库来处理这个JSON数据。

使用RapidJSON的示例代码：

#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include <iostream>
#include <string>int main() {const char* json = "{\"person\":{\"name\":\"John\",\"age\":30,\"address\":{\"street\":\"123 Main St\",\"city\":\"New York\"},\"hobbies\":[\"Reading\",\"Hiking\"]}}";rapidjson::Document doc;doc.Parse(json);if (!doc.HasParseError()) {const rapidjson::Value& person = doc["person"];std::string name = person["name"].GetString();int age = person["age"].GetInt();const rapidjson::Value& address = person["address"];std::string street = address["street"].GetString();std::string city = address["city"].GetString();const rapidjson::Value& hobbies = person["hobbies"];if (hobbies.IsArray()) {for (rapidjson::SizeType i = 0; i < hobbies.Size(); i++) {std::string hobby = hobbies[i].GetString();std::cout << "Hobby " << i + 1 << ": " << hobby << std::endl;}}std::cout << "Name: " << name << ", Age: " << age << std::endl;std::cout << "Address: " << street << ", " << city << std::endl;} else {std::cout << "JSON parse error" << std::endl;}return 0;
}

使用nlohmann/json的示例代码：

#include <nlohmann/json.hpp>
#include <iostream>
#include <string>int main() {std::string json = "{\"person\":{\"name\":\"John\",\"age\":30,\"address\":{\"street\":\"123 Main St\",\"city\":\"New York\"},\"hobbies\":[\"Reading\",\"Hiking\"]}}";nlohmann::json j = nlohmann::json::parse(json);std::string name = j["person"]["name"];int age = j["person"]["age"];std::string street = j["person"]["address"]["street"];std::string city = j["person"]["address"]["city"];for (const auto& hobby : j["person"]["hobbies"]) {std::string hobbyStr = hobby;std::cout << "Hobby: " << hobbyStr << std::endl;}std::cout << "Name: " << name << ", Age: " << age << std::endl;std::cout << "Address: " << street << ", " << city << std::endl;return 0;
}

#include <nlohmann/json.hpp>
#include <iostream>
#include <string>int main() {std::string json = R"({"Header": {"sessionId": "1648612124933560_v20ZmHxNa4yx3","code": 200,"message": "业务服务返回消息:StatusOK"},"Payload": {"groupList": [{"groupName": "巅峰榜","groupTopList": [{"listenNum": 18835312,"showTime": "2022-03-30","songInfos": [{"singerId": 4658,"singerMId": "000ZVS6E1f6f0d","singerName": "杨丞琳","songId": 648765,"songMId": "004XNJ8Y2iD3VL","songName": "匿名的好友"},{"singerId": 143,"singerMId": "003Nz2So3XXYek","singerName": "陈奕迅","songId": 331839675,"songMId": "003UkWuI0E8U0l","songName": "孤勇者"}],"topBannerPic": ".jpg","topHeaderPic": ".jpg","topId": 62,"topName": "飙升榜","totalNum": 100}]}],"msg": "OK","ret": 0,"sessionId": "1648612124933560_v20ZmHxNa4yx3"}})";nlohmann::json j = nlohmann::json::parse(json);if (j.contains("Header") && j.contains("Payload")) {const auto& header = j["Header"];const auto& payload = j["Payload"];std::string sessionId = header["sessionId"];int code = header["code"];std::string message = header["message"];std::string msg = payload["msg"];int ret = payload["ret"];std::string payloadSessionId = payload["sessionId"];const auto& groupList = payload["groupList"];if (groupList.is_array()) {for (const auto& group : groupList) {std::string groupName = group["groupName"];const auto& groupTopList = group["groupTopList"];if (groupTopList.is_array()) {for (const auto& top : groupTopList) {int listenNum = top["listenNum"];std::string showTime = top["showTime"];int topId = top["topId"];std::string topName = top["topName"];int totalNum = top["totalNum"];const auto& songInfos = top["songInfos"];if (songInfos.is_array()) {for (const auto& songInfo : songInfos) {int singerId = songInfo["singerId"];std::string singerMId = songInfo["singerMId"];std::string singerName = songInfo["singerName"];int songId = songInfo["songId"];std::string songMId = songInfo["songMId"];std::string songName = songInfo["songName"];// 打印解析结果std::cout << "Song Info:" << std::endl;std::cout << "Singer ID: " << singerId << std::endl;std::cout << "Singer MId: " << singerMId << std::endl;std::cout << "Singer Name: " << singerName << std::endl;std::cout << "Song ID: " << songId << std::endl;std::cout << "Song MId: " << songMId << std::endl;std::cout << "Song Name: " << songName << std::endl;}} else {std::cout << "songInfos is not an array" << std::endl;}// 打印解析结果std::cout << "Listen Num: " << listenNum << std::endl;std::cout << "Show Time: " << showTime << std::endl;std::cout << "Top ID: " << topId << std::endl;std::cout << "Top Name: " << topName << std::endl;std::cout << "Total Num: " << totalNum << std::endl;}} else {std::cout << "groupTopList is not an array" << std::endl;}// 打印解析结果std::cout << "Group Name: " << groupName << std::endl;}} else {std::cout << "groupList is not an array" << std::endl;}} else {std::cout << "Header or Payload is not present in the JSON" << std::endl;}return 0;
}