QHash <int, class*>

[stampede]

You need to call i.next() before taking the value with i.value() (btw. its in the first example in QHashIterator documentation):

while (i.hasNext()) {
      i.next();
      qDebug()<<i.key();
      Person *per = i.value();
      if( per ){ // better check before dereferencing a pointer
          qDebug()<< "Name: " << per->m_name << "Number: "<<per->m_number;
      }
  }

while (i.hasNext()) {
      i.next();
      qDebug()<<i.key();
      Person *per = i.value();
      if( per ){ // better check before dereferencing a pointer
          qDebug()<< "Name: " << per->m_name << "Number: "<<per->m_number;
      }
  }

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also if I call hash.clear() at the end do I need to delete the value first or clear() will take care of it ?

Yes you need to delete allocated values yourself, QHash does not know what kind of data you keep inside it.