C++ constructor call from another constructor with array initialisation

Question

I am writing a new class using OpenGL, i have two possibilities for my constructor :

VertexObject();
VertexObject(GLuint* vertices,GLuint* elements);

What i would like to do is that VertexObject() calls the other one with an already inisialised array such as

    VertexObject::VertexObject() : 
    VertexObject( 
    (GLuint[]) {
        0, 1, 2,
        2, 3, 0
    },
    (GLuint[]) {
        0, 1, 2,
        2, 3, 0
    }) {}

But it seems C++ won't let me do it, error being 'taking address of temporary array'. I am not even sure what i am asking for is doable but any help will be greatly appreciated.

@Simple Because of non-constance, I think the solution is a bit more complicated - see my answer — ikh
– ikh, Commented Jun 16, 2014 at 15:11

spin_eight · Accepted Answer · 2014-06-16 13:12:32Z

2

I propose you to look at boost library, particularly assign pattern(facilitates initialization of containers) might help.

Here is a small code snippet that might give you grasp of idea:

VertexObjectc(boost::assign::list_of(0)(1)(2)(2)(3)(0).convert_to_container<GLuint>() );

I haven`t tested it.

answered Jun 16, 2014 at 13:12

spin_eight

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2 Comments

aze Over a year ago

The other answer solved my problem but the boost library actually triggered another error : couldn't convert from int to the other type. I don't really have the time to fully understand it but now i know about Boos which seems like a good library. Thanks a lot for the help.

spin_eight Over a year ago

@ user3714670 Your are welcome. Boost worth to be study(at least partly), it provides a lot of great functionality.

eerorika · Accepted Answer · 2014-06-16 13:27:56Z

1

If you deep copy the array in the constructor or if the arrays are never ever modified and VertexObject doesn't take the ownership of the pointers, this should work:

GLuint def_vert[6] = { // static storage
    0, 1, 2,
    2, 3, 0
};
VertexObject::VertexObject() : 
VertexObject(def_vert, def_vert) {}

You can use separate arrays if you want different values for each parameter of course.

answered Jun 16, 2014 at 13:27

eerorika

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3 Comments

aze Over a year ago

Huh i don't know why i didn't think about that, i already use that for the default_shaders, thanks a lot it solved it ^^

ikh Over a year ago

It can be wrong - the parameter of the constructor is not const GLuint *, but GLuint *, so def_vert can be changed. See my answer.

eerorika Over a year ago

@ikh: yes, if the constructor doesn't modify the array, then the parameter should be declared const for the sake of const-correctness. In that case def_vert can be const as well.

ikh · Accepted Answer · 2014-06-16 15:08:13Z

Try this:

// VertexObject.h
class VertexObject
{
private:
    static const GLuint m_default_vertices[6], m_default_elements[6];
    static GLuint *GetDefVertices();
    static GLuint *GetDefElements();
public:
    VertexObject() : VertexObject(GetDefVertices(), GetDefElements()) { }
    ...
};
// VertexObject.cpp
const GLuint VertexObject::m_default_vertices[6] = {
    0, 1, 2,
    2, 3, 0
};
const GLuint VertexObject::m_default_elements[6] = {
    0, 1, 2,
    2, 3, 0
};
GLuint *VertexObject::GetDefVertices()
{
    static thread_local GLuint ar[6];
    memcpy(ar, m_default_vertices, sizeof(ar));
    return ar;
}
GLuint *VertexObject::GetDefElements()
{
    static thread_local GLuint ar[6];
    memcpy(ar, m_default_elements, sizeof(ar));
    return ar;
}

(http://ideone.com/IvujSq)

Note that it works on C++11.

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