[SCIP] Multiple SCIP_ConsData cause heap corruption

[Hendel, Gregor]

Hi Marko,


Marc says off-topic, but I won't erase my answer now 😊


I admit I haven't looked at your minimal working example. In the C world, your easiest option is to introduce distinct structs for each type in the headers


cons_one.h: struct one_data {...}

cons_two.h: struct two_data {...}

...


and to create a constraint data using


struct one_data *mydata;

mydata = malloc(sizeof(struct one_data));


 // constraint creation


SCIPsetConsData(scip, cons_of_type_one, (SCIP_CONSDATA*)mydata);


Whenever the constraint wants to use its above data in the implementation in one.cpp, cast it back to its original type:


struct one_data *mydata = (struct one_data *)SCIPconsGetData(cons);


Note that for all constraint handlers of SCIP, their data implementation is entirely private to the c file, they *NEVER* expose their internal data structure of struct SCIP_ConsData to the world outside. This is why you pass a list of weights, list of binary variables, and a capacity to the Knapsack constraint handler at constraint creation time, but not an object of SCIP_KNAPSACKDATA type, which does not even exist.


Now it's time for C++ guys to tell you a different approach.


Cheers,

Gregor






________________________________
Von: Scip <scip-bounces at zib.de> im Auftrag von Horváth Markó <marko.horvath at sztaki.hu>
Gesendet: Donnerstag, 22. Oktober 2020 10:37:55
An: scip at zib.de
Betreff: [SCIP] Multiple SCIP_ConsData cause heap corruption

Dear All,

I am working on a branch-and-price project using SCIP, but I got stuck
on something. Actually, I reduced my problem to a "simple" C++ issue,
but due to the design of SCIP maybe you have already run into this
problem and know the solution.

So, my problem is that I have three different user-defined constraints
and thus three different user-defined constraint data, that is, three
different structures in three different .cpp files with the same name:
SCIP_ConsData. (Due to the design of SCIP, I must use this name for all
structures). Everything was fine when I used only the first two
constraints (it was also a luck, I guess), however, the third one ruined
everything. The problem is that in runtime these structures are mixed up
which causes a heap corruption.

More precisely, I have three SCIP_ConsData structures in different .cpp
files (say, one.cpp, two.cpp, three.cpp) and when I want to create a new
instance of the corresponding SCIP_ConsData in file two.cpp, the
structure in file one.cpp is going to be created. Later, it will cause a
heap corruption.

What should I do to fix this issue?

I attach a very minimal working example for this phenomenon. I use
Visual Studio 2019 under Windows 10 with C++17 Standard.

Best Regards,
Marko
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