RE: [fltk.general] Callback segfaults when member functions are invoked. [General Use]

[MacArthur, Ian (Leonardo, UK)]

OK, I concur with Nikita's suggestion here...


The "ch1_shift" in this code here:

> void cb_ch1_shift(Fl_Widget*,void*) {
> Ch1Shift = ch1_shift->value();
> }


Is not the same "ch1_shift" that is in this code below, since this one is declared after the one above is used in the callback, and so presumably is not in scope for the callback.
The one above is probably referring to some other variable called "ch1_shift", which I guess is NULL at the point that the callback executes it.

> Fl_Line_Dial *ch1_shift = new Fl_Line_Dial(x,y,40,40);




> It looks functionally identical to me, so something else may have changed of
> which I'm unaware. Both callbacks are outside blocks and so should be
> static. The latter works fine when no member functions are invoked, but
> invoking value() causes the problem.

No, as noted, I suspect that the variable scope is different and hence the function of the code is altered, producing the segfault you report.




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[52mid...@gmail.com]

YES! Thanks, Nikita - removing the "Fl_Line_Dial *" DID do the trick! I'll need a bit of pondering to get the reasons clear in my mind, though.

And BTW congratulations to the FLTK team for a superb piece of kit. A real pleasure to learn and use.


[52mid...@gmail.com]

Thanks to both for the detailed reply, and sorry about the dual post - only just joined the group. I understand what you're saying and will examine it.

Most of my coding for the past decade has been Perl with some assembler. Segfaults don't exist in Perl (that I can recall) and microcontrollers don't even know what segments are, so I've zero experience in debugging this sort of thing.

I'll post back after getting my head around it.