Sqlite3 window problem

[giusepped]

I found a solution but I do not understand why it is working.
First I create a static member function in mainWindow:

bool mainWindow::createConnStatic()
{
	QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
 
}

bool mainWindow::createConnStatic()
{
	QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");

}

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which is declared static in the header file.

Now, at the startup I create a connection by calling this function. db is a member variable.
When I wann change database, I do

QSqlDatabase db =  QSqlDatabase::database();
db.setDatabaseName(s);

QSqlDatabase db =  QSqlDatabase::database();
db.setDatabaseName(s);

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This work pretty well, but is "impossible" to got there by reading the Qt Doc.