Read blob fields from a database with the odbc driver

Greetings, I'm trying to create a program that automatically update a blob field of a table, i know that the data in the blob field is text but don't know much more about it.
is there any way to read/update this field? this is my code so far:

Code:

---

void conecta2::retrieveblob()
{
    conectdbisam();
    QByteArray blob;
    QString line;
    QString line2;
    QString tabla = "sfixed";
    QString pointer = "55542";
    int h,k,o;
    h=0;
    k=1;  //this is the code column that should match with "pointer"
    o=4;  //this is the blob column
    if(db.open())
    {
        QSqlQuery qry;
        if(qry.exec("SELECT * FROM "+tabla))
        {
            QSqlRecord rec = qry.record();
            columna = rec.fieldName(k);
        }
        if(qry.exec("SELECT * FROM "+tabla+" WHERE "+columna+" = '"+pointer+"'"))
        {
            while(qry.next())
            {
                blob= qry.value(o).toByteArray();
                line2 = line.fromAscii(blob);
                qDebug() << "line blob "+line2;
                h++;
                if (h==500)
                break;
            }
        }
    }
    else
    {
        qDebug() << "Error =" << db.lastError().text();
    }
}

---

this return "line blob " meaning that the string line2 is empty, what am I doing wrong?
Thanks in advance