QString.remove() Why not working?

[Noob]

I've got my slot:

void MainWindow::fdelete()
{
    ui->lineEdit->text().remove(ui->lineEdit->text().length() , 1);
}

void MainWindow::fdelete()
{
    ui->lineEdit->text().remove(ui->lineEdit->text().length() , 1);
}

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And i can't figure out, why this is not working? I want to delete the last character on the right. So it has to be the last one added.
The text().length() should return the amount of characters inside the string, so this should be the position of the last one, am I wrong?

thanks for answer.