QString d;
QFile f(QDir::currentPath() + "/input.txt");
if( f.open( QIODevice::ReadOnly | QIODevice::Text ) )
{
    d = f.readAll();
    f.close();
}
auto cutf8 = QTextCodec::codecForName("UTF-8");
auto cw50 = QTextCodec::codecForName("windows-1250");
auto cw51 = QTextCodec::codecForName("windows-1251");

QFile ff(QDir::currentPath() + "/output.txt");
    if( ff.open( QIODevice::WriteOnly | QIODevice::Text ) )
    {
        QTextStream t(&ff);

        QTextStream* tt = new QTextStream(t.device());
        tt->setCodec(cutf8);
        *tt << d << "\r\n";
        tt->flush();
        delete tt;

        tt = new QTextStream(t.device());
        tt->setCodec(cw50);
        *tt << d << "\r\n";
        tt->flush();
        delete tt;

        tt = new QTextStream(t.device());
        tt->setCodec(cw51);
        *tt << d << "\r\n";
        tt->flush();
        delete tt;
    }
    ff.close();