.size（）的左侧必须具有class / struct / union

Question

I've been trying to make a random password generator and so far everything has been going good until I got this error which I can't seem to figure out: left of size must have class/struct/union I've looked around and people have similar problems but I can't seem to find a solution for mine. Any help would is appreciated.

void MainWindow::on_pushButton_2_clicked()
    {
        QString password;

        QString letters[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};
        QString special[] = {'!', '@', '#', '$', '%', '^', '&', '*', '(', ')', '_', '-', '+', '=', '/', '?', '>', '<', '\'', '\"', ';', ':', '`', '~'};
        int numbers[] = {1,2,3,4,5,6,7,8,9,0};

        int length = ui->horizontalSlider_2->value();
        bool douppercase = ui->checkBox_2->isChecked();

        for(int i = 1; i <= length; i++) {
            int selection = roll(1, 3);
            qDebug() << selection;
            QString selectedletter;
            int lettercase;
            int letter;
            switch(selection) {
                case 2:
                    letter = roll(0, special.size());
                    // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                    password += special[letter];
                break;
                case 3:
                    letter = roll(0, numbers.size());
                    // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                    password += numbers[letter];
                break;
                default:
                    letter = roll(0, letters.size());
                    // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
                    selectedletter = letters[letter];
                    if(douppercase)
                        lettercase = roll(1, 2);
                        if(lettercase == 1)
                            selectedletter.toLower();
                        password += selectedletter;
                break;
            }
        }

        ui->lineEdit->setText(password);
    }

    int MainWindow::roll(int min, int max) {
        int randNum = rand()%(max-min + 1) + min;
        return randNum;
    }

Answer 1

letter = roll(0, special.size());

special and letters are arrays. Arrays don't have methods. They don't have class members, they are just arrays.

You are probably looking for:

sizeof(specials)/sizeof(specials[0])

Ditto for letters .

Answer 2

The arrays you have declared (letters/specials/numbers) are C type arrays. They don't have functions or member variables - they are just arrays of QStrings.

If you want a class which wraps arrays then look at std::vector and std::array

Alternatively you can programatically determine the size of the array by doing: sizeof(letters) / sizeof(QString)

Answer 3

You cannot call .size for array. Instead, you can do one of the following for a given array like arr :

sizeof(arr) / sizeof(arr[0])

or

std::end(arr) - std::begin(arr)

and in C++17, one will be able to use:

std::size(arr)

The latter is unified way of getting the size for arrays and other stl containers.