How to check if file is appropriated with database driver in Qt - c++

Question

Assuming I want to open a connection to SQLite3 database in Qt. It will be connected to an existed database dbName.
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
Now I need to set db.setDatabaseName(dbName), where dbName is received through a QFileDialog.
However, as long as dbName is a valid file name, then db.open() is always true. Is there anyway to check if the file dbName is a SQLite3 database, but not of any other type? What I can do now is to execute a query and check for error like:
db.setDatabaseName(dbName);
if (db.open()) {
QSqlQuery qr(db);
if (!qr.exec(".database;")) {
qDebug() << qr.lastError().text();
return false;
}
}
but it won't work if the file is empty.

Answer 1

Qt always uses the SQLITE_OPEN_CREATE flag, so nonexistent or empty files are considered valid (for a new, empty database).
If you don't want to change Qt, or write your own database driver, the only alternative is to manually check for a valid database header in the file.

Answer 2

I had to face the same problem.
In fact, there is two issues :
1/ As CL said, Qt always uses the SQLITE_OPEN_CREATE flag, so if you try to open a database that point to a non-existent file, the database will be created and you get a success.
You can adress this issue by checking if the file exists before open (see QFile::Exists static method)
2/ SQLite use "lazy initialization", so until you make a request on the database, the file is not really opened.
You can adress this issue by executing a simple request right after the database open, and check the result.
If you don't know anything in advance about the database schema, you can try to read one of the "PRAGMA" values : http://www.sqlite.org/pragma.html#pragma_table_info