nlohmann json

1 brief introduction

github Address ：nlohmann/json: JSON for Modern C++ (github.com)

2 Integrate

stay release Download json.hpp File can . Then load the file into the project for use .

3 Use

here , We mainly introduce the serialization and deserialization of custom objects as json Format , So we need to define a data structure .

#pragma once
using namespace std;
#include <string>
#include "../json/json.hpp"
using namespace nlohmann;
namespace models
{
    typedef enum
    {
        male = 0,
        female = 1,
    } gender;

    typedef struct
    {
        string name;
        uint8_t age;
        gender gen;
    } person;
    
    NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE(person, name, age, gen);
}

Pay attention to the last key , With it, you can serialize the structure of custom data .

3.1 Serialize the custom object to json In file

    models::person p{"zhuangjuan", 28, models::gender::female};// Define a person object 
    nlohmann::json j = p;// take person Object to json object 
    ofstream fout("person.json",ios::out);
    fout<<j.dump();// take json Object to string Type written to file 
    fout.close();

3.2 take json File deserialization to object

    string msg;
    ifstream fin("person.json", ios::in);
    fin >> msg;
    fin.close();// take json File read out 
    json j = nlohmann::json::parse(msg);// Convert string to json object 
    models::person p = j.get<models::person>();// take json Object to person object 

4 Be careful

4.1 Serialize the object to json When ,json By default, the structure in is sorted alphabetically , How can I customize sorting , To be further studied

4.2 By default ,json Comments are not allowed in structures . If you have to comment, you need to use “//”. And then the json String conversion to json When the object , You need to pay attention to a parameter . But I tried and I don't know why I still can't ....

json j = nlohmann::json::parse(msg,nullptr,false,true);