hi everyone,
i have init a database and i want to insert data to this database ,i write a code as below, when compiler without any error but can not insert any data
please help me
Qt Code: 
  1. void MainForm::creat_db()
  2. {
  3.   db = QSqlDatabase::addDatabase("QSQLITE");
  4.   #ifdef Q_OS_LINUX
  5.   // store database file into user home folder in Linux
  6.   QString path(QDir::home().path());
  7.   path.append(QDir::separator()).append("my.db.sqlite");
  8.   path = QDir::toNativeSeparators(path);
  9.   db.setDatabaseName(path);
  10.   #else
  11.   // file exists in the application private folder
  12.   db.setDatabaseName("my.db.sqlite");
  13.   #endif
  14.   // Open databasee
  15.   if(!db.open())
  16.   {
  17.       QMessageBox::warning(0, QObject::tr("database error"),db.lastError().text());
  18.   }
  19.  
  20.   QSqlQuery query;
  21.   query.exec("create table db_table "
  22.                   "(id integer primary key, "
  23.                   "start_time varchar(20), "
  24.                   "decription varchar(30), "
  25.                  "finish_time varchar(20))");
  26.  }
  27.  
  28. int MainForm::insert_to_db(QString start_time, QString description, QString finish_time)
  29.  {
  30.  int newId = -1;
  31.  bool ret = false;
  32.  if (db.isOpen())
  33.  {
  34.  // NULL = is the keyword for the autoincrement to generate next value
  35.  QSqlQuery query;
  36.  ret = query.exec(QString("insert into db_table(NULL,'%1','%2','%3')")
  37.                   .arg(start_time).arg(description).arg(finish_time));
  38.  // Get database given autoincrement value
  39.  if (ret)
  40.  {
  41.  newId = query.lastInsertId().toInt();
  42.  }
  43.  }
  44.  return newId;
  45.  }
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and I call them in mainform
Qt Code: 
  1. MainForm::MainForm(QWidget *parent) :
  2.     QMainWindow(parent),
  3.     ui(new Ui::MainForm)
  4. {
  5.     ui-> setupUi(this);
  6.     creat_db();
  7.     insert_to_db("10:10","too high","10:12"); //only test
  8. }
  9. ...........
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