c++ - QTextStream への書き込み

Question

このコードが終了すると、私の QTextStream は空です:

QString line1 = "This is line one";
QString line2 = "This is line two";
QString line3 = "This is line three";

QString outputFilename = "temp.txt";
QFile outputFile(outputFilename);
outputFile.open(QIODevice::WriteOnly);
outputFile.open(QIODevice::ReadWrite);  // This fixes the problem
  QTextStream out1(&outputFile);
   out1  << line1 << endl;
   out1  << line2 << endl;
   out1  << line3 << endl;

outputFile.flush();
QString temp = out1.readAll();           
mainclipboard->setText(temp);
outputFile.close();

ここで、QString temp は空です。私は何を逃したのですか？

答えてくれたハイドに感謝します。