Attempting to use Sqlite backup api from driver handle fails

[jimmytaker]

The answer is already here, but not written explicitly. THE call that makes the difference between crash and no crash is sqlite3_open. Apparently having the sqlite3.dll plugin on one side and the sqlite3.c compiled in on the other (to be able to call any of the sqlite3 API directly messes up or misses some init. So basically what is needed is:
1. Include sqlite code (.c and .h files) in your project
2. Use this snippet after m_Database.open()::

QVariant v = m_Database.driver()->handle();
        if (v.isValid() && strcmp(v.typeName(), "sqlite3*") == 0) {
            // v.data() returns a pointer to the handle
            sqlite3 *handle = *static_cast<sqlite3 **>(v.data());
            if (handle != 0) { // check that it is not NULL
				sqlite3 *p; //without this there is a crash.
				int result = sqlite3_open( ":memory:", &p );
				if (result == SQLITE_OK) {
					sqlite3_close(p);
					//call any API you need on handle.
				} else
                    qDebug() << "Could not sqlite3_open p" << result;
            } else {
                qDebug() << "Could not get sqlite handle";
            }
        } else {
            qDebug() << "handle variant returned typename " << v.typeName();
        }

QVariant v = m_Database.driver()->handle();
        if (v.isValid() && strcmp(v.typeName(), "sqlite3*") == 0) {
            // v.data() returns a pointer to the handle
            sqlite3 *handle = *static_cast<sqlite3 **>(v.data());
            if (handle != 0) { // check that it is not NULL
				sqlite3 *p; //without this there is a crash.
				int result = sqlite3_open( ":memory:", &p );
				if (result == SQLITE_OK) {
					sqlite3_close(p);
					//call any API you need on handle.
				} else
                    qDebug() << "Could not sqlite3_open p" << result;
            } else {
                qDebug() << "Could not get sqlite handle";
            }
        } else {
            qDebug() << "handle variant returned typename " << v.typeName();
        }

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[mohannad]

hello
I still having this problem
with throw exception at this section:

SQLITE_PRIVATE void sqlite3WalEndReadTransaction(Wal *pWal){
sqlite3WalEndWriteTransaction(pWal);
if( pWal->readLock>=0 ){
walUnlockShared(pWal, WAL_READ_LOCK(pWal->readLock));
pWal->readLock = -1;
}
}


and I attempts all your answers

here my code

QSqlDatabase m_db = QSqlDatabase::addDatabase("QSQLITE");

m_db.setDatabaseName(":memory:");
m_db.open();
qDebug() << "create: " << m_db.driverName();

// create a table in the memory DB
QSqlQuery q_create = m_db.exec("CREATE TABLE qdn (id int, name varchar(50))");
qDebug() << "create: " << q_create.lastError();

// populate with some data
QSqlQuery q_insert(m_db);
q_insert.prepare("INSERT INTO qdn (id, name) VALUES (:id, :name)");
q_insert.bindValue(":id", QVariant::fromValue(1));
q_insert.bindValue(":name", "Volker");
qDebug() << "insert volker: " << q_insert.exec();

q_insert.bindValue(":id", QVariant::fromValue(2));
q_insert.bindValue(":name", "Root");
qDebug() << "insert root: " << q_insert.exec();

// get the inner sqlite3 handle(as QVariant)
QVariant v = m_db.driver()->handle();
//// check its validity
if (v.isValid() && strcmp(v.typeName(), "sqlite3*") == 0)
{

// v.data() returns a pointer to the handle
// it is valid, so cast to sqlite3 handle
sqlite3 *handle = *static_cast<sqlite3 **>(v.data());
if (handle != 0)
{

loadOrSaveDb(handle, "d:/backupfrommemory.sqlite", 1);
}
else
{
qDebug() << "Could not get sqlite handle";
}
}

else
{
qDebug() << "handle variant returned typename " << v.typeName();
}
}

also I tried with sqliteDBMemFile as answer but also same error ... so please if I can find help
with thanks