将对象传递给 QT 中的函数会导致分段错误

Question

Thanks in advance for your time. I'm still new to the coding world, so excuse me if I ask something silly or obvious.

I'm coding a small program with QT for manipulating data of a data base. To represent the data I'm using QTableViews. I have a few of them with the same configuration, so I made a function to configure them:

QT 5.12
void MainWindow::configureTableView(QSqlTableModel *model, QTableView *table, QString DBTable)
{
    //Pacients table.
    model = new QSqlTableModel(this);
    model->setTable(DBTable);
    model->setEditStrategy(QSqlTableModel::OnManualSubmit);
    model->select();
    table->setModel(model);
    table->setSortingEnabled(true);
    table->setCornerButtonEnabled(true);
    table->hideColumn(0);
}

I have some QSqlTableModel defined in the mainwindow.h as:

 QSqlTableModel *PatientsTable;
...

I call the function with:

configureTableView(PatientsTable, ui->ClientsTabTableView, "Pacientes");

Program starts and shows OK, but as soon as I try to do anything with the view like set a filter

PatientsTable->setFilter(Search)

where Search is a QString configured by other function based on user input, the program crashes and QT tells me it received a signal from the operative system: SIGSEGV (segmentation fault).

Now when is was coding all of this, at some point I had:

void MainWindow::configureTableView(QTableView *table, QString DBTable)

    PatientsTable = new QSqlTableModel(this);
    PatientsTable->setTable(DBTable);
    PatientsTable->setEditStrategy(QSqlTableModel::OnManualSubmit);
    PatientsTable->select();
    table->setModel(PatientsTable);
    table->setSortingEnabled(true);
    table->setCornerButtonEnabled(true);
    table->hideColumn(0);

which works with no issues at all.

What am I missing? I've been digging for a while now and the code and explanations I found on Internet aren't working. Thanks again for your time!

Answer 1

The problem is that your function does not modify the PatientsTable variable. Just passing a pointer to a function does not let you modify the pointer itself (only what it's pointing to). Simple solution, pass the pointer by reference.

void MainWindow::configureTableView(QSqlTableModel *&model, QTableView *table, QString DBTable)

The alternative (better in my view) would be to return the pointer from the function

QSqlTableModel *MainWindow::configureTableView(QTableView *table, QString DBTable)
{
    QSqlTableModel *model = new QSqlTableModel(this);
    ...
    return model;
}


PatientsTable = configureTableView(ui->ClientsTabTableView, "Pacientes");

It's a very common beginner misunderstanding. Pass pointers to modify what is being pointed to. The pointer itself cannot be modified. In this regard pointers are just like any other kind of variable.