I doubt if QTextStream setAutoDetectUnicode doesn't work

#include "mainwindow.h"
#include "qtextedit.h"
#include "qtextstream.h"
#include "qfile.h"
#include "qstringconverter.h"
#include "qiodevice.h"
#include "qdebug.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{

    textedit = new QTextEdit;
    setCentralWidget(textedit);


    QFile in("memo.txt");

    if (in.open(QFile::WriteOnly)){
        QTextStream instream(&in);
        instream.setEncoding(QStringConverter::Utf16);
        instream.setGenerateByteOrderMark(true);
        instream << "textedit->toPlainText()";
        in.close();
    }


    QFile out("memo.txt");

    if (out.open(QFile::ReadOnly)){
        QTextStream outstream(&out);
        outstream.setAutoDetectUnicode(true);
        bool a = outstream.generateByteOrderMark();
        QStringConverter::Encoding c = outstream.encoding();

        QString t = outstream.readAll();
        textedit->setPlainText(t);
        qDebug() << c << a;
        out.close();
    }
}

MainWindow::~MainWindow()
{
}