Inheritance and STL vector

Question

let's say i got a class "Simple" with this private var : std::vector m_listePoint; which constructor is

Simple(EnumCouleur::tEnumCouleur c,vector<Point> listeP);

(couleur is inherited from her mother class)

i got another class which is "Circle" ( a child class of "Simple"), with 2 vars : 1 Point, 1 radius Here is the constructor i ve tried :

Cercle::Cercle( const Point centre, const double rayon, EnumCouleur::tEnumCouleur v)
{
        m_rayon = rayon;
        vector<Point> liste;
        liste.push_back(centre);
        __super::Simple(v,liste);

}

I got an error saying Simple doesnt have a default constructor.

I know that basically i should do this way :

 Cercle::Cercle( const Point centre, const double rayon, EnumCouleur::tEnumCouleur v) : m_rayon(rayon), Simple(...)

the problem is : how to build the vector then?

This might be a stupid question i don't know, i come from java, this is why i used super and might be bad way...

i ve found it here : http://stackoverflow.com/questions/4424216/c-equivalent-of-super — Niko, Nov 19 '14 at 21:58
you cannot call another constructor from the body of another function, even another constructor. — Mordachai, Nov 19 '14 at 21:58
@Mordachai Well, you can...it just doesn't do what one might expect. — T.C., Nov 19 '14 at 21:59
how can i do then? i want to put my point in a vector, and then send it to "Simple" — Niko, Nov 19 '14 at 22:00
@BWG Do you not know what "body" means? Yes, from the initialize list. No, not from the body. — Mordachai, Nov 19 '14 at 22:07
why it's marked as duplicated now ? the url is nothing about my problem — Niko, Nov 19 '14 at 22:13

score 0 · Accepted Answer · answered Nov 19 '14 at 22:00

0

Use the vector constructor that makes a vector of n copies of an element:

Cercle::Cercle( const Point centre, const double rayon, EnumCouleur::tEnumCouleur v) 
       : m_rayon(rayon), Simple(v, std::vector<Point>(1, centre)) { /* ... */ }

Or, in C++11, use the initializer list constructor:

Cercle::Cercle( const Point centre, const double rayon, EnumCouleur::tEnumCouleur v) 
       : m_rayon(rayon), Simple(v, {centre}) { /* ... */ }

answered Nov 19 '14 at 22:00

T.C.

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how you do if you got 2 values to put in the vector ? – Niko Nov 19 '14 at 22:28
@Niko The initializer list method still works. Otherwise, write a helper function that constructs and returns the vector. – T.C. Nov 19 '14 at 22:30

Mooing Duck · Answer 2 · 2014-11-19T23:01:47.343

Vector has a useful constructor here: vector(size_type count, const T& value, <irrelevent>) that makes it easy to construct a vector with a single element: vector<Point>(1, centre).

Like so:

Cercle::Cercle( const Point centre, const double rayon, EnumCouleur::tEnumCouleur v)
    :m_rayon(rayon),
    Simple(v, vector<Point>(1, centre))
{
}

If you have multiple elements, make a simpler helper function or use an initializer_list

initializer_list

Rect::Rect( const Point topleft, const Point botright, EnumCouleur::tEnumCouleur v)
    :m_rayon(rayon),
    Simple(v, {topleft, botright})
{
}

helper function:

std::vector<Point> make_from_two(point one, point two) {
    vector<Point> liste;
    liste.push_back(one);
    liste.push_back(two);
    return liste;
} 

Rect::Rect( const Point topleft, const Point botright, EnumCouleur::tEnumCouleur v)
    :m_rayon(rayon),
    Simple(v, make_from_two(topleft, botright))
{
}

how you do if you got 2 values to put in the vector ? – Niko Nov 19 '14 at 22:27 — Niko, Nov 19 '14 at 22:27

Inheritance and STL vector

2 Answers2