rapidjson 使用

来源于这篇博客
https://blog.csdn.net/qq_35703954/article/details/82691030?ops_request_misc=%7B%22request%5Fid%22%3A%22163004801416780357227263%22%2C%22scm%22%3A%2220140713.130102334.pc%5Fblog.%22%7D&request_id=163004801416780357227263&biz_id=0&utm_medium=distribute.pc_search_result.none-task-blog-2_blogfirst_rank_v2~rank_v29-1-82691030.pc_v2_rank_blog_default&utm_term=json&spm=1018.2226.3001.4450

rapidjson生成复杂的json串

{
    "name":"jack",//常规的
    "age":18,
    "sub":["a","b"],//value是数组
    "elp":[ {"a":"A","b":"B"},//value是一个数组且里面每个元素又是一个json格式
            {"c":"C","d":"D"},
          ]
}

//#include "rapidjson/stringbuffer.h"
//#include "rapidjson/writer.h"


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

#include <iostream>


std::string build_json_msg(){

    rapidjson::Document doc;//生成DOM元素
    doc.SetObject();
    rapidjson::Document::AllocatorType& allocator = doc.GetAllocator();//生成一个分配器

    //构建键值对
    doc.AddMember("name","jack",allocator);
    doc.AddMember("age",18,allocator);
    //====构建数组元素====["1","2"]
        rapidjson::Value array_sub(rapidjson::kArrayType);//创建一个数组类型对象
        array_sub.PushBack("a",allocator);
        array_sub.PushBack("b",allocator);
    //================
    doc.AddMember("sub",array_sub,allocator);
    //====构建数组object===[{"1":2,},{}]
        rapidjson::Value array_json(rapidjson::kArrayType);
            rapidjson::Value obj(rapidjson::kObjectType);//每一个数组里面是一个json格式
                obj.AddMember("a","A",allocator);
                obj.AddMember("b","B",allocator);
            array_json.PushBack(obj,allocator);

            rapidjson::Value obj1(rapidjson::kObjectType);//每一个数组里面是一个json格式
                obj1.AddMember("c","C",allocator);
                obj1.AddMember("d","D",allocator);
            array_json.PushBack(obj1,allocator);
//            array_json.PushBack(obj1,allocator);
    doc.AddMember("elp",array_json,allocator);


    rapidjson::StringBuffer s;
    rapidjson::Writer<rapidjson::StringBuffer> writer(s);
    doc.Accept(writer);

    return std::string(s.GetString());

}

int main()
{
    std::string str_json = build_json_msg();
    std::cout<<str_json<<std::endl;

    std::cout<<"hello world"<<std::endl;
    return 0;
}

我用的qt,其中.pro如下：

QT -= gui

CONFIG += c++11 console
CONFIG -= app_bundle

# The following define makes your compiler emit warnings if you use
# any feature of Qt which as been marked deprecated (the exact warnings
# depend on your compiler). Please consult the documentation of the
# deprecated API in order to know how to port your code away from it.
DEFINES += QT_DEPRECATED_WARNINGS

# You can also make your code fail to compile if you use deprecated APIs.
# In order to do so, uncomment the following line.
# You can also select to disable deprecated APIs only up to a certain version of Qt.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += main.cpp

INCLUDEPATH += /data_2/project_202009/project/3rdparty/

程序跑起来打印如下：

{"name":"jack","age":18,"sub":["a","b"],"elp":[{"a":"A","b":"B"},{"c":"C","d":"D"}]}
hello world
按 <RETURN> 来关闭窗口...

在网站json.cn可以格式化显示json：

{
    "name":"jack",
    "age":18,
    "sub":[
        "a",
        "b"
    ],
    "elp":[
        {
            "a":"A",
            "b":"B"
        },
        {
            "c":"C",
            "d":"D"
        }
    ]
}

在生成的时候我们需要几个十分重要的对象，Document、AllocatorType。刚开始的三行代码是比较固定的，先申明一个doc和一个分配器。

rapidjson::Document doc;//生成DOM元素
doc.SetObject();
rapidjson::Document::AllocatorType& allocator = doc.GetAllocator();//生成一个分配器

我们添加json元素主要通过doc.AddMember(key,value,分配器)的形式来生成。如果json格式很简单，那么代码也很简单，如下：

doc.AddMember("name","jack",allocator);
doc.AddMember("age",18,allocator);

但是，如果涉及到数组。就需要注意一下。首先，我们需要创建一个数组类型的对象。然后把数组里面的内容PushBack进去。最后同样通过doc.AddMember()添加进去。但是value却变成了array_sub.说明AddMember()的第二个参数，不仅可以是值还可以是对象。

rapidjson::Value array_sub(rapidjson::kArrayType);//创建一个数组类型对象
		array_sub.PushBack("a",allocator);
		array_sub.PushBack("b",allocator);
	//================
doc.AddMember("sub",array_sub,allocator);

同样，如果数组里面是json串，该怎么办呢？其实写法按着上面的逻辑来，看上面的代码，只不过把‘a’换成object类型的。具体写法如下：

//====构建数组object===[{"1":2,},{}]
		rapidjson::Value array_json(rapidjson::kArrayType);
			rapidjson::Value obj(rapidjson::kObjectType);//每一个数组里面是一个json格式
				obj.AddMember("a","A",allocator);
				obj.AddMember("b","B",allocator);
			array_json.PushBack(obj,allocator);
 
			rapidjson::Value obj1(rapidjson::kObjectType);//每一个数组里面是一个json格式
				obj1.AddMember("c","C",allocator);
				obj1.AddMember("d","D",allocator);
			array_json.PushBack(obj1,allocator);
			array_json.PushBack(obj1,allocator);
	doc.AddMember("elp",array_json,allocator);

读写json参考链接：
https://www.cnblogs.com/fnlingnzb-learner/p/10334988.html