jsoncpp serialize class in vector

//Book.h
#include <iostream>
#include <jsoncpp/json/json.h>

using namespace std;

class Book
{
public:
    int Idx;
    unsigned long long Id;
    char *Name;
    char *Abstract;
    char *Content;
    char *Comment;
    char *Author;
    char *ISBN;
    char *Topic;

    void BookSerialize(Json::Value &obj)
    {
        obj["Idx"]=Idx;
        obj["Id"]=Id;
        obj["Name"]=Name;
        obj["Abstract"]=Abstract;
        obj["Content"]=Content;
        obj["Author"]=Author;
        obj["ISBN"]=ISBN;
        obj["Topic"]=Topic;
    }
};


//main.cpp
#include <ctime>
#include <iostream>
#include <jsoncpp/json/json.h>
#include <fstream>
#include <functional>
#include <string.h>
#include <uuid/uuid.h>
#include <vector>
#include "Model/Book.h"

using namespace std;

char *uuidValue = (char *)malloc(40);

char *getUuid()
{
    uuid_t newUUID;
    uuid_generate(newUUID);
    uuid_unparse(newUUID,uuidValue);
    return uuidValue;
}

char* dtValue=(char*)malloc(20);
char* getTimeNow()
{
    time_t rawTime=time(nullptr);
    struct tm tmInfo=*localtime(&rawTime);
    strftime(dtValue,20,"%Y%m%d%H%M%S",&tmInfo);
    return dtValue;
}

void getBookVector(vector<Book> &vec,int len)
{
    for(int i=0;i<len;i++)
    {
        Book bk;
        bk.Idx=i;
        bk.Idx=(unsigned long long)i*i;
        bk.Abstract=(char*)malloc(40);
        bk.Author=(char*)malloc(40);
        bk.Comment=(char*)malloc(40);
        bk.Content=(char*)malloc(40);
        bk.ISBN=(char*)malloc(40);
        bk.Name=(char*)malloc(40);
        bk.Topic=(char*)malloc(40);
        strcpy(bk.Abstract,getUuid());
        strcpy(bk.Author,getUuid());
        strcpy(bk.Comment,getUuid());
        strcpy(bk.Content,getUuid());
        strcpy(bk.ISBN,getUuid());
        strcpy(bk.Name,getUuid());
        strcpy(bk.Topic,getUuid());
        vec.push_back(bk);
    }
}

void logMsg(string fileName,string msg)
{
    fstream wFile(fileName,ios::app);
    if(!wFile.is_open())
    {
        cout<<"Open "<<fileName<<" failed!"<<endl;
        return;
    }

    wFile<<msg<<endl;
    wFile.close();
    cout<<getTimeNow()<<" write into "<<fileName<<" succeed!"<<endl;
}

void SerializeVector(int len)
{
    vector<Book> vec;
    getBookVector(std::ref(vec),len);

    Json::Value rootObj;
    
    for(int i=0;i<len;i++)
    {
        Json::Value obj;
        vec[i].BookSerialize(std::ref(obj));
        rootObj.append(obj);
    }

    Json::StyledWriter sWriter;
    string jsonValue=sWriter.write(rootObj);
    string fileName(getTimeNow());
    fileName.append(".txt");
    logMsg(fileName,jsonValue);
}

int main(int args,char ** argv)
{
    SerializeVector(atoi(argv[1]));
}

Compile in g++

g++ -g -std=c++2a -I. *.cpp ./Model/*.h -o h1 -ljsoncpp -luuid

Run 

./h1 100