C access violation error, but not in debug mode

Question

I have this code:

MountedJob* new_MountedJob(Job** job){
    MountedJob* new = malloc(sizeof(MountedJob*));
    printf("ok ");
    new->job = *job;
    printf("not ok");
    new->neededTools = new->job->toolSet;
    new->baseInstance = new->job->baseInstance;
    new->cj = new->baseInstance->C - hashset_size(new->neededTools);
    hashset_new(&new->unneededTools);
    return new;
}

It is executed 10 times, each time for a Job passed as an argument. They come from a iterated list and are generated exactly the same way. At the 3rd iteration, new->job = *job; crashes with access violation error code (0xc0000005). The problem is that it works just fine in debug mode so I have no clue what the problem could be. Especially that it works for the 2 first iterations, that's unconsistent I really don't understand.

Thank you.

There is no space allocated for the actual structure `new` is pointing to. And don't use name `new`. — Eugene Sh., Oct 26 '18 at 15:34

score 3 · Accepted Answer · answered Oct 26 '18 at 15:34

3

You are not allocating the proper size:

MountedJob* new = malloc(sizeof(MountedJob));

Otherwise, you only allocated one pointer, instead of a whole structure.

answered Oct 26 '18 at 15:34

Matthieu Brucher

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`sizeof(MountedJob)`, as in my code. I remove the `*` already. – Matthieu Brucher Oct 26 '18 at 15:38
Thank you it works now. How come it did work in debug mode though ? Is it because it allocates more memory in some way ? – Henri.D Oct 26 '18 at 15:51
Debug mode will work differently indeed. You may want to have a look at address sanitizer or valgrind to flag these memory issues. – Matthieu Brucher Oct 26 '18 at 15:58

score 2 · Answer 2 · answered Oct 26 '18 at 15:34

2

You are allocated memory of sizeof(MountedJob*) ie: a pointer size NOT the size of the structure, so then when accessing it, it is likely overwriting places it should not be.

It should be

MountedJob* new = malloc(sizeof(MountedJob));

answered Oct 26 '18 at 15:34

lostbard

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Is Mavis Beacon still teaching? ;-) – Fiddling Bits Oct 26 '18 at 15:36

C access violation error, but not in debug mode

2 Answers2