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Re: [fltk.coredev] Double free of groups

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Re: Double free of groups Rob McDonald Mar 16, 2023  
 
On Thursday, March 16, 2023 at 10:53:01 AM UTC-7 Albrecht Schlosser wrote:
Back on topic:

My proposed changes: since I'm not sure that we are using the same version of the Cartesian project, following is the full code of the two mentioned d'tors with fixes.

```
Cartesian.cpp-728-Ca_X_Axis::~Ca_X_Axis(){ Cartesian.cpp-729- if(canvas_){ Cartesian.cpp-730- Ca_ObjectChain *ochain=canvas_->first_object_; Cartesian.cpp-731- Ca_ObjectChain *next; Cartesian.cpp-732- Ca_ObjectChain *previous=0; Cartesian.cpp-733- while (ochain){ Cartesian.cpp-734- next=ochain->next; Cartesian.cpp-735- if(ochain->object->x_axis_==this){ Cartesian.cpp-736- delete ochain->object; Cartesian.cpp-737- if(previous) Cartesian.cpp-738- previous->next=next; Cartesian.cpp-739- else Cartesian.cpp-740- canvas_->first_object_=next; Cartesian.cpp:741: // delete ochain; // would cause double free <<<<<<< Cartesian.cpp-742- } Cartesian.cpp-743- ochain=next; Cartesian.cpp-744- } Cartesian.cpp-745- } Cartesian.cpp-746-} -- Cartesian.cpp-1051-Ca_Y_Axis::~Ca_Y_Axis(){ Cartesian.cpp-1052- if(canvas_){ Cartesian.cpp-1053- Ca_ObjectChain *ochain=canvas_->first_object_; Cartesian.cpp-1054- Ca_ObjectChain *next; Cartesian.cpp-1055- Ca_ObjectChain *previous=0; Cartesian.cpp-1056- while (ochain){ Cartesian.cpp-1057- next=ochain->next; Cartesian.cpp-1058- if(ochain->object->y_axis_==this){ Cartesian.cpp-1059- delete ochain->object; Cartesian.cpp-1060- if(previous) Cartesian.cpp-1061- previous->next=next; Cartesian.cpp-1062- else Cartesian.cpp-1063- canvas_->first_object_=next; Cartesian.cpp:1064: // delete ochain; // would cause double free <<<<<<< Cartesian.cpp-1065- } Cartesian.cpp-1066- ochain=next; Cartesian.cpp-1067- } Cartesian.cpp-1068- } Cartesian.cpp-1069-} ```


This fix works for me.

It took a while for me to figure out what he was doing -- it feels much more complex than a singly linked list should be.  It took even longer to convince myself that the fix is right.

As you say -- it is hard to understand why the FLTK change would trigger this.  

I also removed everything to do with previous -- it looks like a remnant of a doubly linked list, but it isn't used now.

Thanks again,

Rob


 

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