invalid operands to binary expression ('const char *' and 'QString')

[TheCipo76]

Hi, i'va a problem to compare different type of text..

if (!aDatabase.open())
        {
        // Messaggio Errore
        QMessageBox::critical(this, "Errore", aDatabase.lastError().text());
        return;
        }
    //COMBO CODICE - DA DATABASE
    QSqlQuery q;
    q.prepare("Select CODICE from ARTICOLI where Cliente == " & ui->comboBox_Cliente->currentText() &  " order by CODICE");
    if (ui->comboBox_Cliente->currentText() == "")
        {
        QMessageBox::warning(this, "Errore", "Selezionare prima il Cliente!");
        return;
        }
    if (q.exec())
        {
            QSqlQueryModel *TModel = new QSqlQueryModel(this);
            TModel->setQuery(q);
            ui->comboBox_Codice->setModel(TModel);
        }

compiling i've this error but idon't know how solve it..

.../regtemciclo.cpp:81: error: invalid operands to binary expression ('const char *' and 'QString')
q.prepare("Select CODICE from ARTICOLI where Cliente == " & ui->comboBox_Cliente->currentText() & " order by CODICE");
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

anyone help me please??

[JonB]

@TheCipo76

q.prepare("Select CODICE from ARTICOLI where Cliente == " & ui->comboBox_Cliente->currentText() &  " order by CODICE");

Let's start with: What in the world is that & operator supposed to be? If it's string concatenation, that's + in C++, we're not in Visual Basic here! :)

Then you might want to look at http://doc.qt.io/qt-5/qstring.html#arg as a neater way of accomplishing it.:

QString("Select CODICE from ARTICOLI where Cliente == %1 order by CODICE").arg(ui->comboBox_Cliente->currentText())

Up to you, matter of preference.

Finally, you sure == is the right operator to pass in your query? Last time I looked SQL's operator is =, but you may know better for your SQL provider.

[TheCipo76]

ooops.. you're right!!
Thank you

[JonB]

@TheCipo76
Check what I've added about your SQL == operator?

Also, if your ui->comboBox_Cliente->currentText() is some literal text (as opposed to a SQL expression), won't you need SQL quote marks around it, like say:

QString("Select CODICE from ARTICOLI where Cliente == '%1' order by CODICE").arg(ui->comboBox_Cliente->currentText())

And even then it won't work right if the literal string contains a ' character....