I'am stuck.
I have a class with two QList

Qt Code: 
  1. class Formulas
  2. {
  3. public:
  4.     Formulas();
  5.     ~Formulas();
  6.  
  7.     QString m_formula;
  8.     QList<QString> m_variables;
  9.     QList<QString> m_values;
  10. };
  11.  
  12. QDataStream & operator<< (QDataStream& stream, const Formulas& formula);
  13. QDataStream & operator>> (QDataStream& stream, Formulas& formula);
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Qt Code: 
  1. QDataStream & operator<< (QDataStream& stream, const Formulas& formula)
  2. {
  3.     QString str;
  4.     stream<<formula.m_formula;
  5.     stream<<str.setNum(formula.m_variables.size());
  6.  
  7.     for(int i=0;i<formula.m_variables.size();i++)
  8.     {
  9.         stream<<formula.m_values.at(i);
  10.         stream<<formula.m_variables.at(i);
  11.     }
  12.  
  13.     return stream;
  14. }
  15.  
  16. //QList<Formulas> lista_formulas;
  17.  
  18. QDataStream & operator>> (QDataStream& stream, Formulas& formula)
  19. {
  20.     QString str;
  21.     int size;
  22.     QString val;
  23.     QString var;
  24.     stream>>formula.m_formula;
  25.     stream>>str;
  26.     size=str.toInt();
  27.  
  28.     for(int i=0;i<size;i++)
  29.     {
  30.         stream>>val;
  31.         formula.m_values.append(val);
  32.         stream>>var;
  33.         formula.m_variables.append(var);
  34.     }
  35.  
  36.     return stream;
  37. }
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Qt Code: 
  1. formulas_dlg::formulas_dlg(QWidget *parent) :
  2.     QDialog(parent),
  3.     m_ui(new Ui::formulas_dlg)
  4. {
  5.     m_ui->setupUi(this);
  6.  .....
  7.     QFile file("file.dat");
  8.     file.open(QIODevice::ReadOnly);
  9.     //QDataStream in(&file,&form_teste);    // read the data serialized from the file
  11.     in<<form_teste;
  12.     file.close();
  13. // form_teste is of type Formulas defined in formulas_dlg class
  14.     QMessageBox::about(this,"",form_teste.m_formula);
  15. ......
  16. }
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Qt Code: 
  1. void formulas_dlg::on_buttonBox_accepted()
  2. {
  3.     QMessageBox::about(this,"","ok");// check if this function is called
  4.  
  5.     form_teste.m_formula="xpto";//check if this data is written to file, and it's not file stays empty
  6.  
  7.     QFile file("file.dat");
  8.     file.open(QIODevice::WriteOnly);
  9.     QDataStream out;   // we will serialize the data into the file
  10.     out << form_teste;
  11.     file.close();
  12.  
  13. }
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it compiles without erros, but the file is still empty after on_buttonBox_accepted is called.
Any ideas to solve this????????????????

Bta, this is the easy part. I really dont want to serialize the type "Formulas form_teste"
but the type "QList<Formulas> form_teste";
I am just doing it iin steps and trying to solve this error first.

Thank you