C++ 使用 rapidjson 生成 json 並解析
- 2019 年 11 月 6 日
- 筆記
概述
使用 rapidjson 生成 json 並對其進行解析。
常用函數
AddMember
- 功能：往對象中添加一個鍵值對。GenericValue& rapidjson::GenericValue< Encoding, Allocator >::AddMember( GenericValue< Encoding, Allocator > & name, GenericValue< Encoding, Allocator > & value, Allocator & allocator )
- 函數原型
- 函數參數
- name 是鍵的名稱
- value 是對應鍵的值
- allocator 用來分配記憶體的分配器，必須與前面使用的相同。
SetString
- 功能：將此值設置為字元串，且複製原字元串。
- 函數原型
GenericValue& rapidjson::GenericValue< Encoding, Allocator >::SetString( const Ch * s, SizeType length, Allocator & allocator )
- 函數參數
- s 是原字元串
- length 是原字元串的長度，包括後面的空字元
- allocator 分配器
程式碼
#include <iostream> #include <string> #include <fstream> #include <windows.h> #include "rapidjson/prettywriter.h" #include "rapidjson/document.h" #include "rapidjson/istreamwrapper.h" using namespace std; using namespace rapidjson; //----------------------------------------------------------------------------- void AddBasicType(Document &d, Document::AllocatorType & allocator) { d.AddMember("digit", 3, allocator); // 添加整型數據 d.AddMember("height", 170.5, allocator); // 添加浮點類型 d.AddMember("subject1", "math", allocator); // 添加字元串類型,常量方式 string strSubject = "English"; Value valueSubject(kStringType); valueSubject.SetString(strSubject.c_str(), strSubject.size(), allocator); if (!valueSubject.IsNull()) { d.AddMember("subject2", valueSubject, allocator); // 添加字元串類型，變數方式，不能直接對變數進行添加，類型不對 } } //----------------------------------------------------------------------------- void AddObjectType(Document &d, Document::AllocatorType & allocator) { Value valueObject(kObjectType); valueObject.AddMember("sex", "male", allocator); valueObject.AddMember("weight", 95, allocator); d.AddMember("info", valueObject, allocator); } //----------------------------------------------------------------------------- void AddStringArrayType(Document &d, Document::AllocatorType & allocator) { Value valueStr(kStringType); // 單個字元串 Value valueStrArray(kArrayType); // 字元串數組 string strExtraSubject1 = "電腦"; string strExtraSubject2 = "音樂"; string strExtraSubject3 = "體育"; valueStr.SetString(strExtraSubject1.c_str(), strExtraSubject1.size(), allocator); valueStrArray.PushBack(valueStr, allocator); valueStr.SetString(strExtraSubject2.c_str(), strExtraSubject2.size(), allocator); valueStrArray.PushBack(valueStr, allocator); valueStr.SetString(strExtraSubject3.c_str(), strExtraSubject3.size(), allocator); valueStrArray.PushBack(valueStr, allocator); d.AddMember("extraSubject", valueStrArray, allocator); } //----------------------------------------------------------------------------- void AddObjectArrayType(Document &d, Document::AllocatorType & allocator) { Value valueObjectArray(kArrayType); for (int i = 0; i < 3; i++) { Value valueSingleObject(kObjectType); valueSingleObject.AddMember("score", i * 40, allocator); if (i == 0) { valueSingleObject.AddMember("difficulty", "hard", allocator); } else if (i == 1) { valueSingleObject.AddMember("difficulty", "abnormal", allocator); } else { valueSingleObject.AddMember("difficulty", "easy", allocator); } valueObjectArray.PushBack(valueSingleObject, allocator); } d.AddMember("subjectInfo", valueObjectArray, allocator); } //----------------------------------------------------------------------------- void ParseBasicType(Document &d, string jsonData) { if (!d.Parse(jsonData.data()).HasParseError()) { // 解析整型 if (d.HasMember("digit") && d["digit"].IsInt()) { cout << "digit = " << d["digit"].GetInt() << endl; } // 解析浮點型 if (d.HasMember("height") && d["height"].IsDouble()) { cout << "height = " << d["height"].GetDouble() << endl; } // 解析字元串類型 if (d.HasMember("subject1") && d["subject1"].IsString()) { cout << "subject1 = " << d["subject1"].GetString() << endl; } if (d.HasMember("subject2") && d["subject1"].IsString()) { cout << "subject2 = " << d["subject2"].GetString() << endl; } } } //----------------------------------------------------------------------------- void ParseObjectType(Document &d, string jsonData) { if (d.HasMember("info") && d["info"].IsObject()) { const Value& resInfo = d["info"]; // 獲取對象 if (resInfo.HasMember("sex") && resInfo["sex"].IsString()) { cout << "resInfo.sex = " << resInfo["sex"].GetString() << endl; } if (resInfo.HasMember("weight") && resInfo["weight"].IsInt()) { cout << "resInfo.weight = " << resInfo["weight"].GetInt() << endl; } } } //----------------------------------------------------------------------------- void ParseStringArrayType(Document &d, string jsonData) { if (d.HasMember("extraSubject") && d["extraSubject"].IsArray()) { const Value& valueStrArray = d["extraSubject"]; size_t len = valueStrArray.Size(); // 獲取數組長度 for (size_t i = 0; i < len; i++) { cout << "extraSubject[" << i << "] = " << valueStrArray[i].GetString() << endl; } } } //----------------------------------------------------------------------------- void ParseObjectArrayType(Document &d, string jsonData) { if (d.HasMember("subjectInfo") && d["subjectInfo"].IsArray()) { const Value& valueObjectArray = d["subjectInfo"]; // 獲取對象數組 size_t len = valueObjectArray.Size(); for (size_t i = 0; i < len; i++) { const Value& object = valueObjectArray[i]; // 每一個元素都是一個對象 if (object.IsObject()) { cout << "subjectInfo[" << i << "]: "; if (object.HasMember("score") && object["score"].IsInt()) { cout << "score = " << object["score"].GetInt(); } if (object.HasMember("difficulty") && object["difficulty"].IsString()) { cout << " difficulty = " << object["difficulty"].GetString(); } } cout << endl; } } } //----------------------------------------------------------------------------- int main() { Document d; d.SetObject(); wstring wsValue; Document::AllocatorType &allocator = d.GetAllocator(); // 獲取分配器 AddBasicType(d, allocator); // 添加基本類型 AddObjectType(d, allocator); // 添加對象類型，對象中有基本數據類型 AddStringArrayType(d, allocator); // 添加字元串數組類型，數組中的每一個元素是一個字元串 AddObjectArrayType(d, allocator); // 添加對象數組類型，數組中的每一個元素是一個對象 // StringBuffer是一個簡單的輸出流。它分配一個記憶體緩衝區，供寫入整個JSON。 // 可使用GetString()來獲取該緩衝區。 StringBuffer strBuf; Writer<StringBuffer> writer(strBuf); d.Accept(writer); string jsonData = strBuf.GetString(); cout << jsonData << endl << endl; ParseBasicType(d, jsonData); // 解析基本類型 ParseObjectType(d, jsonData); // 解析對象類型 ParseStringArrayType(d, jsonData); // 解析字元串數組類型 ParseObjectArrayType(d, jsonData); // 解析對象數組類型 }
生成的 json 數據
{ "digit": 3, "height": 170.5, "subject1": "math", "subject2": "English", "info": { "sex": "male", "weight": 95 }, "extraSubject": [ "電腦", "音樂", "體育" ], "subjectInfo": [ { "score": 0, "difficulty": "hard" }, { "score": 40, "difficulty": "abnormal" }, { "score": 80, "difficulty": "easy" } ] }
