Need some help with c++/qt5 code

[Raphael Kubo da Costa]

Dimitry Andric <dim at FreeBSD.org> writes:

> On 14 Apr 2016, at 13:58, Shane Ambler <FreeBSD at ShaneWare.Biz> wrote:
>> 
>> Hi there, while I am comfortable with c and python, I only know a little
>> c++ and could use some help.
> ...
>> class TPanelFactory
>> {
>>    QString m_panelType;
>>    static QMap<QString, TPanelFactory *> m_table;
>> 
>> public:
>>    TPanelFactory(QString panelType);
>>    ~TPanelFactory();
>> 
>>    QString getPanelType() const { return m_panelType; }
>> 
>>    virtual void initialize(TPanel *panel) = 0;
>>    virtual TPanel *createPanel(QWidget *parent);
>>    static TPanel *createPanel(QWidget *parent, QString panelType);
>> };
>> 
>> m_table is then in the source file as
>> 
>> QMap<QString, TPanelFactory *> TPanelFactory::m_table;
>> 
>> The segfault happens in the constructor -
>> 
>> TPanelFactory::TPanelFactory(QString panelType)
>>    : m_panelType(panelType)
>> {
>>    assert(m_table.count(panelType) == 0);
>>    m_table[m_panelType] = this;
>> }
>> 
>> the last line causes the segfault, if I comment it out then main() is
>> entered, but I expect removing that line will bite back soon enough.
>> 
>> How can I get this working?
>> 
>> Why would this fail on FreeBSD but not OSX or windows?
>
> Most likely the program depends on the initialization order of global
> constructors.  This is bad practice, and should be avoided.

I agree. Maybe using Q_GLOBAL_STATIC helps?

- Remove m_table from TPanelFactory.
- In pane.cpp, you do something like this:

  typedef QMap<QString, TPanelFactory *> PanelMapType;
  Q_GLOBAL_STATIC(PanelMapType, s_panelMap);

  you then need to replace uses of m_table with s_panelMap and use
  s_panelMap->operation() instead of m_table.operation().