Hi Mario,
Hmm, it looks like you haven't really understood what I wrote you. You use
the struct but allocate it with BU_GET() on the heap and don't use its
intersect flag. But what is really bad is that you don't free it if it
won't be used any more.
BTW, do you have a Chinese OS version? Your diff files contain Chinese
comments.
Regards,
Daniel
2017-09-21 14:13 GMT+02:00 Mario Meissner <mr.rash....@gmail.com>:
> Hi Daniel.
>
> Thank you for your response. Negative values may have been only due to
> using the wrong formatting tag while printing values. I have cleaned up
> some unused variables and fixed the intersection by using your suggestion.
>
> Mass is 0 in the total_weight variable, as if the code wasn't really
> adding up my segment_density values correctly. I might have deleted some
> important code related to the storing or reading of the values. I will
> double check on that now.
> Attached goes current version of my code.
>
> Mario.
>
> On 21 September 2017 at 13:03, Daniel Roßberg <danielmrossb...@gmail.com>
> wrote:
>
>> Hi Mario,
>>
>> I have been trying to track down the reason why some densities are
>>> negative. A few questions I have ended up asking myself:
>>>
>>> - Is it possible for MAGNITUDE() to return a negative number? It would
>>> make no sense to me, but I suspect it's happening.
>>>
>>
>> No, MAGNITUDE() is the square root of a (necessarily) positive value.
>> You can safely assume it to be not negative.
>>
>> - In my little function intersection I noticed that I am returning a
>>> pointer to a local variable, that could be destroyed in any moment after
>>> the call ends. Instead of that, I want to return a safe variable. How do I
>>> do that in this case?
>>>
>>> I don't understand why it doesn't let me return directly the variable
>>> point_t. It's a pointer, because it's an array, right? As it didn't let me
>>> return the point, I decided to return a pointer to the point instead,
>>> however as I mentioned this is not safe, so I have to change it now. Any
>>> explanation on why I can't return the point, and what I should do to make
>>> it safe?
>>>
>>
>> Well, there is a standard solution for this kind of issue: Putting the
>> data on the heap, e.g.
>> point_t *intersect = (point_t *) bu_malloc(sizeof(point_t),
>> "intersection");
>> with the disadvantage that the caller has explicitly to free the memory
>> with bu_free().
>>
>> It's true that C functions can't return arrays (because of historic
>> reason). But, returning an array wouldn't help you here as you are using
>> the function's return as a flag for intersection too. On the other hand,
>> structs can be returned:
>> struct intersection_t {
>> int intersect;
>> point_t intersection_point;
>> };
>>
>> struct intersection_t intersection(point_t p0, point_t p1, point_t
>> p_co, vect_t p_no) {
>> ....
>> should work.
>>
>>
>>> Finally, I think I could need some help regarding the negative values
>>> issue, at least once I'm sure the two points above aren't the cause.
>>>
>>
>> Feel free to ask ;)
>>
>>
>> Regards,
>> Daniel
>>
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