Text is not displayed in QPlainTextEdit, what's the problem?

Question

Qt

Wrote a function that takes a string. After concatenation, it should be displayed with the date in the QPlainTextEdit. put cout, the variable is not empty. what is needed is displayed. But Plynedith doesn't have anything.
Here is the function:

void *WSystemMessage::log(QString strg) {
    QDateTime *t = new QDateTime();
    QString str = t->currentDateTime().toString("dd.MM.yyyy hh:mm:ss") + " : ";
    str = str + strg;
    cout << str.toStdString() << endl;
    this->findChild<QPlainTextEdit*>("WSystemMessage_plainTextEdit")
            ->appendPlainText(str);
}