Cannot reboot system from C++ – Docker

I’ve a C++ program running in a docker container. I want to reboot container via my program but I cannot.

Dockerfile:

FROM gcc

WORKDIR /client
COPY . .

RUN apt-get update && apt-get install qt5-qmake qtbase5-dev libmosquitto-dev -y

RUN qmake mainapp.pro && make
RUN chmod +x docker-entrypoint.sh

docker-entrypoint.sh

#!/bin/bash
./mainapp -e

Here is my reboot function (cleared from unnecessary codes):

    Logger::getInstance()->write(QString("Sync"));
    sync();
    Logger::getInstance()->write(QString("Setuid"));
    setuid(0);
    Logger::getInstance()->write(QString("RB_AUTOBOOT"));
    reboot(RB_AUTOBOOT);
    Logger::getInstance()->write(QString("Reboot"));
    system("reboot");

I can see ALL the outputs and then it prints an error message. Here is the error message:

System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to connect to bus: Host is down
Failed to talk to init daemon.

I tried to reboot from container but it doesn’t work as well:

root@93501f6d7fc8:/client# reboot
System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to connect to bus: Host is down
Failed to talk to init daemon.
root@93501f6d7fc8:/client# shutdown -r
System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to connect to bus: Host is down

I’ve searched this problem and tried most of the suggestions but they didn’t solved my problem.

I am open to all your ideas and suggestions.