rapidjson

一、简介

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。RapidJSON是跨平台的，支持Windows、Linux、Mac OS X及iOS、Android。writer和prettywriter都是将JSON数据打包为字符串的方法。
官网：https://rapidjson.org/zh-cn/index.html

1.1 write和prettywriter的区别

1、writer将JSON打包为字符串，将其整个数据打包为一行。
2、prettywriter将JSON打包为字符串，将数据中的每个key占一行的输出。

二、用法

目标json

{
    "Int": 1, 
    "Double": 12.0000001, 
    "String": "This is a string", 
    "Object": {
        "name": "qq849635649", 
        "age": 25
    }, 
    "IntArray": [
        10, 
        20, 
        30
    ], 
    "DoubleArray": [
        1, 
        2, 
        3
    ], 
    "StringArray": [
        "one", 
        "two", 
        "three"
    ], 
    "MixedArray": [
        "one", 
        50, 
        false, 
        12.005
    ], 
    "People": [
        {
            "name": "qq849635649", 
            "age": 0, 
            "sex": true
        }, 
        {
            "name": "qq849635649", 
            "age": 10, 
            "sex": false
        }, 
        {
            "name": "qq849635649", 
            "age": 20, 
            "sex": true
        }
    ]
}

2.1 写json协议：方式一

#include "rapidjson/stringbuffer.h"
#include "rapidjson/writer.h"
#include <iostream>
#include <string>
 
using namespace std;
 
void Serialize_1()
{
    rapidjson::StringBuffer strBuf;
    rapidjson::Writer<rapidjson::StringBuffer> writer(strBuf);
 
    writer.StartObject();
 
    //1. 整数类型
    writer.Key("Int");
    writer.Int(1);
 
    //2. 浮点类型
    writer.Key("Double");
    writer.Double(12.0000001);
 
    //3. 字符串类型
    writer.Key("String");
    writer.String("This is a string");
 
    //4. 结构体类型
    writer.Key("Object");
    writer.StartObject();
    writer.Key("name");
    writer.String("qq849635649");
    writer.Key("age");
    writer.Int(25);
    writer.EndObject();
 
    //5. 数组类型
    //5.1 整型数组
    writer.Key("IntArray");
    writer.StartArray();
    //顺序写入即可
    writer.Int(10);
    writer.Int(20);
    writer.Int(30);
    writer.EndArray();
 
    //5.2 浮点型数组
    writer.Key("DoubleArray");
    writer.StartArray();
    for(int i = 1; i < 4; i++)
    {
        writer.Double(i * 1.0);
    }
    writer.EndArray();
 
    //5.3 字符串数组
    writer.Key("StringArray");
    writer.StartArray();
    writer.String("one");
    writer.String("two");
    writer.String("three");
    writer.EndArray();
 
    //5.4 混合型数组
    //这说明了，一个json数组内容是不限制类型的
    writer.Key("MixedArray");
    writer.StartArray();
    writer.String("one");
    writer.Int(50);
    writer.Bool(false);
    writer.Double(12.005);
    writer.EndArray();
 
    //5.5 结构体数组
    writer.Key("People");
    writer.StartArray();
    for(int i = 0; i < 3; i++)
    {
        writer.StartObject();
        writer.Key("name");
        writer.String("qq849635649");
        writer.Key("age");
        writer.Int(i * 10);
        writer.Key("sex");
        writer.Bool((i % 2) == 0);
        writer.EndObject();
    }
    writer.EndArray();
 
    writer.EndObject();
 
    string data = strBuf.GetString();
    cout << data << endl;
}

2.2 写json协议：方式二

 
#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/writer.h"
 
 
void Serialize_2()
{
    rapidjson::Document doc;
    doc.SetObject();
    rapidjson::Document::AllocatorType& allocator = doc.GetAllocator();
 
    //1. 整型类型
    doc.AddMember("Int", 1, allocator);
 
    //2. 浮点类型
    doc.AddMember("Double", 12.00001, allocator);
 
    //3. 字符串类型
    //正确方式
    string str= "This is a string";
    rapidjson::Value str_value(rapidjson::kStringType);
    str_value.SetString(str.c_str(), str.size());
    if(!str_value.IsNull())
    {
        doc.AddMember("String", str_value, allocator);
    }
    /**
     *    注：以下方式不正确，可能成功，也可能失败，因为字符串写入json要重新开辟内存，
     * 如果使用该方式的话，当数据是字符串常量的话是没问题的，如果为变量就会显示乱码，所
     * 以为保险起见，我们显式的分配内存(无需释放)
     */
    //doc.AddMember("String", str.data(), allocator);
 
    //4. 结构体类型
    rapidjson::Value object(rapidjson::kObjectType);
    object.AddMember("name", "qq849635649", allocator); //注：常量是没有问题的
    object.AddMember("age", 25, allocator);
    doc.AddMember("Object", object, allocator);
 
    //5. 数组类型
    //5.1 整型数组
    rapidjson::Value IntArray(rapidjson::kArrayType);
    IntArray.PushBack(10, allocator);
    IntArray.PushBack(20, allocator);
    IntArray.PushBack(30, allocator);
    doc.AddMember("IntArray", IntArray, allocator);
 
    //5.2 浮点型数组
    rapidjson::Value DoubleArray(rapidjson::kArrayType);
    DoubleArray.PushBack(1.0, allocator);
    DoubleArray.PushBack(2.0, allocator);
    DoubleArray.PushBack(3.0, allocator);
    doc.AddMember("DoubleArray", DoubleArray, allocator);
 
    //5.3 字符型数组
    rapidjson::Value StringArray(rapidjson::kArrayType);
    string strValue1 = "one";
    string strValue2 = "two";
    string strValue3 = "three";
    str_value.SetString(strValue1.c_str(), strValue1.size());
    StringArray.PushBack(str_value, allocator);
    str_value.SetString(strValue2.c_str(), strValue2.size());
    StringArray.PushBack(str_value, allocator);
    str_value.SetString(strValue3.c_str(), strValue3.size());
    StringArray.PushBack(str_value, allocator);
    doc.AddMember("StringArray", StringArray, allocator);
 
    //5.4 结构体数组
    rapidjson::Value ObjectArray(rapidjson::kArrayType);
    for(int i = 1; i < 4; i++)
    {
        rapidjson::Value obj(rapidjson::kObjectType);
        obj.AddMember("name", "qq849635649", allocator);//注：常量是没有问题的
        obj.AddMember("age", i * 10, allocator);
        ObjectArray.PushBack(obj, allocator);
    }
    doc.AddMember("ObjectArray", ObjectArray, allocator);
 
    rapidjson::StringBuffer strBuf;
    rapidjson::Writer<rapidjson::StringBuffer> writer(strBuf);
    doc.Accept(writer);
 
    string data = strBuf.GetString();
    cout << data << endl;
}

2.3 解析json协议：方式一

#include "rapidjson/document.h"
#include "rapidjson/stringbuffer.h"
#include "rapidjson/writer.h"
 
string data =
        "{\"Int\":1,"
        "\"Double\":12.0000001,"
        "\"String\":\"This is a string\","
        "\"Object\":{\"name\":\"qq849635649\",\"age\":25},"
        "\"IntArray\":[10,20,30],"
        "\"DoubleArray\":[1.0,2.0,3.0],"
        "\"StringArray\":[\"one\",\"two\",\"three\"],"
        "\"MixedArray\":[\"one\",50,false,12.005],"
        "\"People\":[{\"name\":\"qq849635649\",\"age\":0,\"sex\":true},"
        "{\"name\":\"qq849635649\",\"age\":10,\"sex\":false},"
        "{\"name\":\"qq849635649\",\"age\":20,\"sex\":true}]}";
 
void parse() {
    //创建解析对象
    rapidjson::Document doc;
    //首先进行解析，没有解析错误才能进行具体字段的解析
    if(!doc.Parse(data.data()).HasParseError())
    {
        //1. 解析整数
        if(doc.HasMember("Int") && doc["Int"].IsInt())
        {
            cout << "Int = " << doc["Int"].GetInt() << endl;
        }
        //2. 解析浮点型
        if(doc.HasMember("Double") && doc["Double"].IsDouble())
        {
            cout << "Double = " << doc["Double"].GetDouble() << endl;
        }
        //3. 解析字符串
        if(doc.HasMember("String") && doc["String"].IsString())
        {
            cout << "String = " << doc["String"].GetString() << endl;
        }
        //4. 解析结构体
        if(doc.HasMember("Object") && doc["Object"].IsObject())
        {
            const rapidjson::Value& object = doc["Object"];
            if(object.HasMember("name") && object["name"].IsString())
            {
                cout << "Object.name = " << object["name"].GetString() << endl;
            }
            if(object.HasMember("age") && object["age"].IsInt())
            {
                cout << "Object.age = " << object["age"].GetInt() << endl;
            }
        }
        //5. 解析数组类型
        //5.1 整型数组类型
        if(doc.HasMember("IntArray") && doc["IntArray"].IsArray())
        {
            //5.1.1 将字段转换成为rapidjson::Value类型
            const rapidjson::Value& array = doc["IntArray"];
            //5.1.2 获取数组长度
            size_t len = array.Size();
            //5.1.3 根据下标遍历，注意将元素转换为相应类型，即需要调用GetInt()
            for(size_t i = 0; i < len; i++)
            {
                cout << "IntArray[" << i << "] = " << array[i].GetInt() << endl;
            }
        }
        //5.2 浮点型数组类型
        if(doc.HasMember("DoubleArray") && doc["DoubleArray"].IsArray())
        {
            const rapidjson::Value& array = doc["DoubleArray"];
            size_t len = array.Size();
            for(size_t i = 0; i < len; i++)
            {
                //为防止类型不匹配，一般会添加类型校验
                if(array[i].IsDouble())
                {
                    cout << "DoubleArray[" << i << "] = " << array[i].GetDouble() << endl;
                }
            }
        }
        //5.3 字符串数组类型
        if(doc.HasMember("StringArray") && doc["StringArray"].IsArray())
        {
            const rapidjson::Value& array = doc["StringArray"];
            size_t len = array.Size();
            for(size_t i = 0; i < len; i++)
            {
                //为防止类型不匹配，一般会添加类型校验
                if(array[i].IsString())
                {
                    cout << "StringArray[" << i << "] = " << array[i].GetString() << endl;
                }
            }
        }
        //5.4 混合型
        if(doc.HasMember("MixedArray") && doc["MixedArray"].IsArray())
        {
            const rapidjson::Value& array = doc["MixedArray"];
            size_t len = array.Size();
            for(size_t i = 0; i < len; i++)
            {
                //为防止类型不匹配，一般会添加类型校验
                if(array[i].IsString())
                {
                    cout << "MixedArray[" << i << "] = " << array[i].GetString() << endl;
                }
                else if(array[i].IsBool())
                {
                    cout << "MixedArray[" << i << "] = " << array[i].GetBool() << endl;
                }
                else if(array[i].IsInt())
                {
                    cout << "MixedArray[" << i << "] = " << array[i].GetInt() << endl;
                }
                else if(array[i].IsDouble())
                {
                    cout << "MixedArray[" << i << "] = " << array[i].GetDouble() << endl;
                }
            }
        }
        //5.5 结构体数组类型
        if(doc.HasMember("People") && doc["People"].IsArray())
        {
            const rapidjson::Value& array = doc["People"];
            size_t len = array.Size();
            for(size_t i = 0; i < len; i++)
            {
                const rapidjson::Value& object = array[i];
                //为防止类型不匹配，一般会添加类型校验
                if(object.IsObject())
                {
                    cout << "ObjectArray[" << i << "]: ";
                    if(object.HasMember("name") && object["name"].IsString())
                    {
                        cout << "name=" << object["name"].GetString();
                    }
                    if(object.HasMember("age") && object["age"].IsInt())
                    {
                        cout << ", age=" << object["age"].GetInt();
                    }
                    if(object.HasMember("sex") && object["sex"].IsBool())
                    {
                        cout << ", sex="  << (object["sex"].GetBool() ? "男" : "女") << endl;
                    }
                }
            }
        }
    }
    /**
     *    最后注意：因为rapidjson不会做安全校验，所以要自己做安全校验，以int整型为例
     * “if(object.HasMember("age") && object["age"].IsInt()) {}”
     * 这句校验很重要，既要校验有该子段，也要校验类型正确，否则会引发程序崩溃
     */
}

2.4 解析json协议：方式二

//遍历解析
void parse_1()
{
    // 这个是用于遍历json数组，用于不知道key的前提下
    string data = "{\"name\":\"qq849635649\",\"age\":20,\"sex\":true}";
    rapidjson::Document dom;
    if(! dom.Parse(data.data()).HasParseError())
    {
        for (rapidjson::Value::ConstMemberIterator iter = dom.MemberBegin(); iter != dom.MemberEnd(); ++iter)
        {
            string name = (iter->name).GetString();
            const rapidjson::Value& value = iter->value;
            if(value.IsString())
            {
                cout << name << " : " << value.GetString() << endl;
            }
            else if(value.IsInt())
            {
                cout << name << " : " << value.GetInt() << endl;
            }
            else if(value.IsBool())
            {
                cout << name << " : " << value.GetBool() << endl;
            }
        }
    }
}

2.5 对某个数据进行修改

// rapidjson/example/simpledom/simpledom.cpp`
#include "rapidjson/document.h"
#include "rapidjson/writer.h"
#include "rapidjson/stringbuffer.h"
#include <iostream>
 
using namespace rapidjson;
 
int main() {
    // 1. 把 JSON 解析至 DOM。
    const char* json = "{\"project\":\"rapidjson\",\"stars\":10}";
    Document d;
    d.Parse(json);
 
    // 2. 利用 DOM 作出修改。
    Value& s = d["stars"];
    s.SetInt(s.GetInt() + 1);
 
    // 3. 把 DOM 转换（stringify）成 JSON。
    StringBuffer buffer;
    Writer<StringBuffer> writer(buffer);
    d.Accept(writer);
 
    // Output {"project":"rapidjson","stars":11}
    std::cout << buffer.GetString() << std::endl;
    return 0;
}