Check if Vector_3 is assigned

[petrasvestartas]

Hi,

I have a simple question.
How can I check if a CGAL_Kernel::Vector_3 is assigned?

For example I declare variable (first case)
CGAL_Kernel::Vector_3 v;
and like this (second case):
CGAL_Kernel::Vector_3 v(0,0,1);

Is there any way to know if a user initialized the object or not?
In the first case the return value would be false, in the second true.

Is there a shorter way that doing this?
bool isValid = ((v.x()+v.y()+v.z())<0.0001);

[petrasvestartas]

Anyone?

[afabri]

You cannot check. We had a discussion (or even github issue?) about initializing with NaN to make debugging easier, but didnt conclude.

[lrineau]

There is nothing general, in C++, that can tell you if a variable was initialized or not.

If that is important for you, then use special class templates std::optional or boost::optional: the value-initialized (default-constructed) std::optional has the "empty" state.

[petrasvestartas]

Thank you @afabri and @lrineau

I will use a sum of coordinates as a check, it works fine for my current case, as they are initial all zeros.

Thank you for your response.

[lrineau]

Note that the vector with coordinates (1, 0, -1) has the sum of coordinates equal to 0, as well as (0, 1,-1) and (1, - 1, 0). In fact, there is a full set of vectors like that: any combination of those three vectors, and that is the vector plane of equation x+y+z=0. You should use the equation v==CGAL::ORIGIN instead, so that only the null vector is detected by the criterion.

[petrasvestartas]

@lrineau Thank you for pointing this out, now I understand why I had plenty of random errors that I did not understood.
Your suggestion gives error because v==CGAL::ORIGIN CGAL::ORIGIN is of a type of origin, not a vector (type is not the same) .
Would it work if I use bool is_set = v != CGAL_Vector(0,0,0)?

Another question I have is also a beginner level.
How can I get a pointer of a vector?
If I write auto ptr = &v;
I see that the auto type is again CGAL_Vector, not an address of a vector.

[lrineau]

Sorry, for a vectors that is v==CGAL::NULL_VECTOR. ORIGIN is for points.

[petrasvestartas]

@lrineau Thanks this works.

How about the second part of the question about pointers?

would it be enough to write CGAL_Vector* pointer = &v;

[petrasvestartas]

It was a silly question, I know the answer.

[petrasvestartas]

@lrineau

I checked again this:

CGAL_Vector dir;//not set
bool dirSet = dir != CGAL::NULL_VECTOR;

And this produces true;

[lrineau]

There is nothing that guarantees that an non-initialized CGAL object will have its coordinates zeroed, and that is for efficiency reasons: the default-constructor leaves the coordinates uninitialized.

As I said, if it really matters for you to detect when a variable is left uninitialized, then you need to:

• either manually initialize yourself all the values to a sentinel value (using a Nan, std::numeric_limits<double>::quiet_NaN() for example, for all three coordinates),
• or use a class template like std::optional<CGAL_Vector> or boost::optional<CGAL_Vector> so that you can easily detect the "empty state" of a variable.