c++ 使用 rapidjson 生成 json 并解析

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"
    }
  ]
}