c++ 使用rapidjson对数据序列化和反序列化（vs2109）

  RapidJSON是腾讯开源的一个高效的C++ JSON解析器及生成器，它是只有头文件的C++库，综合性能是最好的。

1. 安装

在NuGet中为项目安装tencent.rapidjson

2. 引用头文件

#include <rapidjson/document.h>
#include <rapidjson/memorystream.h>
#include <rapidjson/prettywriter.h>

3. 头文件定义

添加测试json字符串和类型对应数组

// 测试json字符串
const char* strJson = "{\"name\":\"MenAngel\",\"age\":23,\"hobbys\":[\"语文\",\"数学\",\"英语\",54],\"scores\":{\"数学\":\"90.6\",\"英语\":\"100.0\", \"语文\":\"80.0\"}}";

// 数据类型，和 rapidjson的enum Type 相对应
static const char* kTypeNames[] = { "Null", "False", "True", "Object", "Array", "String", "Number" };

4.  修改JSON 内容

/// <summary>
///  修改JSON 内容
/// </summary>
void MyRapidJson::alterJson()
{
    rapidjson::Document doc;
    doc.Parse(strJson);
    cout << "修改前： " << strJson <<"\n" << endl;

    // 修改内容

    rapidjson::Value::MemberIterator iter = doc.FindMember("name");
    if (iter != doc.MemberEnd())
        doc["name"] = "张三";

    iter = doc.FindMember("age");
    if (iter != doc.MemberEnd())
    {
        rapidjson::Value& v1 = iter->value;
        v1 = "40";
    }

    // 修改后的内容写入 StringBuffer 中
    rapidjson::StringBuffer buffer;
    rapidjson::Writer<rapidjson::StringBuffer> writer(buffer);
    doc.Accept(writer);

    cout <<"修改后： " << buffer.GetString() << "\n" << endl;
}

运行结果：

{"name":"张三","age":"40","hobbys":["语文","数学","英语",54],"scores":{"数学":"90.6","英语":"100.0","语文":"80.0"}}

5. 生成 json 数据

/// <summary>
/// 生成JSON数据
/// </summary>
void MyRapidJson::createJson()
{
    // 1.准备数据
    string name = "王五";
    string gender = "boy";
    int age = 23;
    bool student = true;
    vector<string> hobbys = { "语文","数学","英语" };
    map<string, double> scores = { {"语文",80},{"数学",90},{"英语",100} };

    //2.初始化DOM
    rapidjson::Document doc;
    rapidjson::Document::AllocatorType& allocator = doc.GetAllocator();
    doc.SetObject();

    // 添加数据
    /* 字符串添加 */ 
    rapidjson::Value tempValue1;
    tempValue1.SetString(name.c_str(), allocator);
    doc.AddMember("name", tempValue1, allocator);

    rapidjson::Value tempValue2(rapidjson::kStringType);
    tempValue2.SetString(gender.c_str(), allocator);
    doc.AddMember(rapidjson::StringRef("gender"), tempValue2, allocator);

    /* 数字类型添加 */
    doc.AddMember("age", age, allocator);

    /* bool 类型 */
    rapidjson::Value tempValueStu(rapidjson::kTrueType);
    tempValueStu.SetBool(student);
    doc.AddMember(rapidjson::StringRef("student"), tempValueStu, allocator);

    /* Array 添加数据 */
    rapidjson::Value tempValue3(rapidjson::kArrayType);
    for (auto hobby : hobbys)
    {
        rapidjson::Value hobbyValue(rapidjson::kStringType);
        hobbyValue.SetString(hobby.c_str(), allocator);
        tempValue3.PushBack(hobbyValue, allocator);
    }
    doc.AddMember("hobbys", tempValue3, allocator);

	/* Object 添加 */
	rapidjson::Value tempValue4(rapidjson::kObjectType);
	tempValue4.SetObject();
	for (auto score : scores)
	{
		//rapidjson::Value scoreName(rapidjson::kStringType);
		//scoreName.SetString(score.first.c_str(), allocator);
		//tempValue4.AddMember(scoreName, score.second, allocator);

        // 方法二
		rapidjson::Value scoreName(rapidjson::kStringType);
		scoreName.SetString(score.first.c_str(), allocator);

		rapidjson::Value scoreValue(rapidjson::kStringType);
        char charValue[20];
        itoa(score.second, charValue,10);
		scoreValue.SetString(charValue, allocator);
		tempValue4.AddMember(scoreName, scoreValue, allocator);
	}
    doc.AddMember("scores", tempValue4, allocator);

    // 写入 StringBuffer
    rapidjson::StringBuffer strBuffer;
    rapidjson::Writer<rapidjson::StringBuffer> writer(strBuffer);
    doc.Accept(writer);

    cout << strBuffer.GetString() << "\n" << endl;

    string outFileName = "C:\\Users\\Administrator\\Desktop\\creatJson.txt";
    ofstream outfile(outFileName, std::ios::trunc);
    outfile << strBuffer.GetString() << endl;
    outfile.flush();
    outfile.close(); 
}

运行结果：

{"name":"王五","gender":"boy","age":23,"student":true,"hobbys":["语文","数学","英语"],"scores":{"数学":"90","英语":"100","语文":"80"}}

6. json 数据解析

/// <summary>
/// 查询json 内容
/// </summary>
void MyRapidJson::searchJson()
{
    rapidjson::Document doc;
    if (doc.Parse(strJson).HasParseError())
    {
        std::cout << "json 解析错误" << std::endl;
        return;
    }

    cout << "doc 的属性成员有 " << doc.MemberCount() << "个!" << endl;

    vector<string> propertyName;
    int i = 0;
    for (rapidjson::Value::MemberIterator iter = doc.MemberBegin(); iter != doc.MemberEnd(); ++iter)
    {
        cout << ++i << "、 " << iter->name.GetString() << "    is " << kTypeNames[iter->value.GetType()] << endl;
        propertyName.push_back(iter->name.GetString());
    }
    cout << endl;

    for (rapidjson::Value::MemberIterator iter = doc.MemberBegin(); iter != doc.MemberEnd(); ++iter)
    {
        if (iter->value.GetType() == rapidjson::kObjectType || iter->value.GetType() == rapidjson::kArrayType)
            cout << iter->name.GetString() << " : " << endl;
        else 
            cout << iter->name.GetString() << " : ";

        DfsDocument(std::move(iter->value));
    }
}

/// <summary>
///  遍历里面的内容
/// </summary>
/// <param name="val"></param>
void MyRapidJson::DfsDocument(rapidjson::Value val)
{
	if (!val.GetType())
		return;

	switch (val.GetType()) {
	case rapidjson::kNumberType:
		cout << val.GetInt() << endl;
		break;
	case rapidjson::kStringType:
		cout << val.GetString() << endl;
		break;
	case rapidjson::kArrayType:
		for (rapidjson::Value::ValueIterator itr = val.GetArray().begin();
			itr != val.GetArray().end(); ++itr) {
			rapidjson::Value a;
			a = *itr;
			DfsDocument(std::move(a));
		}
		break;
	case rapidjson::kObjectType:
		for (rapidjson::Value::MemberIterator itr = val.GetObject().begin();
			itr != val.GetObject().end(); ++itr) {
			cout << itr->name.GetString() << " ";
			rapidjson::Value a;
			a = itr->value;
			DfsDocument(std::move(a));
		}
	default:
		break;
	}
}

运行结果

这里需要注意： 

object 类型json字符串中，“数字类型” 需转为 “字符串”，否则查询时会报错。

7.  rapidjson 的其他使用方法

/// <summary>
/// json 属性
/// </summary>
void MyRapidJson::JsonAttribute()
{
    rapidjson::Document doc;
    if (doc.Parse(strJson).HasParseError())
    {
        std::cout << "json 解析错误" << std::endl;
        return;
    }

    // 成员判断
    if (doc.HasMember("hobbys") && !doc["hobbys"].Empty())
        cout << "doc[\"hobbys\"] is not empty!" << "\n" << endl;
    else
        cout << "doc[\"hobbys\"] 不存在。" << "\n" << endl;

    //7.Array的大小
    if (doc["hobbys"].IsArray())
    {
        cout << "doc[\"hobbys\"].Capacity() =  \"  Array的容量及大小：\" " << doc["hobbys"].Capacity() << " 项" << endl;
        cout << "doc[\"hobbys\"].Size() =  \"  Array的容量及大小：\" " << doc["hobbys"].Size() << " 项" << endl;
    }


    // 字符串长度获取
    cout << doc["name"].GetString()  <<"  字符串长度 ：" << doc["name"].GetStringLength() << endl;

    //4.查询某个成员是否存在
    rapidjson::Value::MemberIterator iter = doc.FindMember("scores");
    if (iter != doc.MemberEnd())
    {
        cout << iter->name.GetString() << " : " << endl;
        DfsDocument(std::move(iter->value));
    }
    else
        cout << "Not Finded!" << endl;

    // 相同判断
    if (doc["name"].GetString() == string("MenAngel") &&
        doc["name"] == "MenAngel" && 
        strcmp(doc["name"].GetString(),"MenAngel") == 0)
    {
        cout << "判断为相等" << endl;
    }

}

运行结果：

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