c++ 使用 rapidjson 生成 json 并解析
2019-10-08 本文已影响0人
云胡同学
概述
使用 rapidjson 生成 json 并对其进行解析。
常用函数
AddMember
- 功能：往对象中添加一个键值对。
- 函数原型
GenericValue& rapidjson::GenericValue< Encoding, Allocator >::AddMember(
GenericValue< Encoding, Allocator > & name,
GenericValue< Encoding, Allocator > & value,
Allocator & allocator
)
- 函数参数
- name 是键的名称
- value 是对应键的值
- allocator 用来分配内存的分配器，必须与前面使用的相同。
SetString
- 功能：将此值设置为字符串，且复制原字符串。
- 函数原型
GenericValue& rapidjson::GenericValue< Encoding, Allocator >::SetString(
const Ch * s,
SizeType length,
Allocator & allocator
)
- 函数参数
- s 是原字符串
- length 是原字符串的长度，包括后面的空字符
- allocator 分配器
代码
#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); // 添加整型数据
d.AddMember("height", 170.5, allocator); // 添加浮点类型
d.AddMember("subject1", "math", allocator); // 添加字符串类型,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); // 添加字符串类型，变量方式，不能直接对变量进行添加，类型不对
}
}
//-----------------------------------------------------------------------------
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); // 单个字符串
Value valueStrArray(kArrayType); // 字符串数组
string strExtraSubject1 = "计算机";
string strExtraSubject2 = "音乐";
string strExtraSubject3 = "体育";
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;
}
// 解析浮点型
if (d.HasMember("height") && d["height"].IsDouble())
{
cout << "height = " << d["height"].GetDouble() << endl;
}
// 解析字符串类型
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"]; // 获取对象
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(); // 获取数组长度
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"]; // 获取对象数组
size_t len = valueObjectArray.Size();
for (size_t i = 0; i < len; i++)
{
const Value& object = valueObjectArray[i]; // 每一个元素都是一个对象
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(); // 获取分配器
AddBasicType(d, allocator); // 添加基本类型
AddObjectType(d, allocator); // 添加对象类型，对象中有基本数据类型
AddStringArrayType(d, allocator); // 添加字符串数组类型，数组中的每一个元素是一个字符串
AddObjectArrayType(d, allocator); // 添加对象数组类型，数组中的每一个元素是一个对象
// StringBuffer是一个简单的输出流。它分配一个内存缓冲区，供写入整个JSON。
// 可使用GetString()来获取该缓冲区。
StringBuffer strBuf;
Writer<StringBuffer> writer(strBuf);
d.Accept(writer);
string jsonData = strBuf.GetString();
cout << jsonData << endl << endl;
ParseBasicType(d, jsonData); // 解析基本类型
ParseObjectType(d, jsonData); // 解析对象类型
ParseStringArrayType(d, jsonData); // 解析字符串数组类型
ParseObjectArrayType(d, jsonData); // 解析对象数组类型
}
生成的 json 数据
{
"digit": 3,
"height": 170.5,
"subject1": "math",
"subject2": "English",
"info": {
"sex": "male",
"weight": 95
},
"extraSubject": [
"计算机",
"音乐",
"体育"
],
"subjectInfo": [
{
"score": 0,
"difficulty": "hard"
},
{
"score": 40,
"difficulty": "abnormal"
},
{
"score": 80,
"difficulty": "easy"
}
]
}
