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QTextEdit: press Ctrl+/ to add // to each line of selection

  • It is a common operation to commented out code in IDE

  • Moderators

    Are you asking how to implement that or... ?

  • @sonichy
    You will write code to recognize the Ctrl+/ key press on your QTextEdit, then get the currently selected lines and go through them line-by-line inserting the // at the start of each line.

  • @JonB

    void MdiChild::keyPressEvent(QKeyEvent *e)
        if ((e->modifiers() & Qt::ControlModifier) && e->key() == Qt::Key_Slash) {
            QString s = textCursor().selection().toPlainText();
            QStringList SL = s.split("\n");
            for(int i=0; i<SL.length(); i++){
                    s =;
                    s = "//" +;
                if(i<SL.length()-1) s.append("\n");
        } else {
            return QPlainTextEdit::keyPressEvent(e);

  • @sonichy
    In principle what you have written looks about right to me. However, depending on what you want, I think this is missing a couple of facilities from what I would expect a "comment/uncomment" to do having used it in other editors:

    1. If your start position is in the middle of a line, or there is no selection just where the text caret is, I think your code inserts a // in the middle of a line. That's not right. They tend to go backwards from the start point to find the beginning of that line, and comment the whole line that way.

    2. Your code decides whether to insert/remove a // ("toggle") from each line depending on what each line starts with. When you have a block like:

    // a comment
    some code
    // another comment
    some more code

    you will come out with

     a comment
    //some code
     another comment
    //some more code

    which is not great. I think others look at whether the first line is or is not presently commented, and then apply (the reverse) of that to every line from then on, rather than "toggle* each line individually, so it would come out more like:

    //// a comment
    //some code
    //// another comment
    //some more code

    ready to be uncommented on a second key press. Have a play and see what you think.

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