Const initialization of an array of objects

[colt]

Hello, I am trying to do a constant initialization of an array of "Vec3f" instances. Currently, I tried to implement it based on the code of a const initialization of an int array:

#include "Vec3f.h"
#include "GeometricObjects.h"

class BVolume {
   public:
      BVolume () {}
   private:
      Vec2f slabs [8];
      static const Vec3f normals [8];
      int min_triangle, max_triangle;
};
   const Vec3f BVolume::normals [8] = {{1,0,0},{0,1,0},{1,0,0},{0,1,0},{1,0,0},{0,1,0},{1,0,0},{0,1,0}};

where Vec3f it is a triple of floats with the following constructors:

class Vec3f {
   public:
      inline Vec3f () : x (0), y (0), z (0) {}
      inline Vec3f (const float xx, const float yy, const float zz) : x (xx), y (yy), z (zz)  { }
....
....

When I try to compile this code, this error shows up:

obj/Debug/Scene.o||In function `Vec3f':|
/media/34GB/demos/asmfrt/Vec3f.h|8|multiple definition of `BVolume::normals'|

where this line 8 is the one of the first Vec3f constructor .

So I am actually trying to implement a second constructor with the line const Vec3f BVolume::normals [8] = ...... ?. To what I shall change that so it doesn't make the compiler confused?

[mbozzi]

Static member data that is not inline must be defined exactly once, in one source file. In this case, constexpr implies inline.
static constexpr Vec3f normals [8] = { ... };

[colt]

It did not work: /media/34GB/demos/asmfrt/BVolume.h|18|error: ‘constexpr’ does not name a type|

[mbozzi]

Obviously, to rely on inline variables, your compiler has to support C++17.

Instead, define the variable in exactly one source file. Look up any tutorial that teaches how to define static data members.

Also update your compiler.

[colt]

I changed it to

static const Vec3f normals [7] = {{1,0,0},{0,1,0},{0,0,1},{SQRT3_3,SQRT3_3,SQRT3_3},{-SQRT3_3,SQRT3_3,SQRT3_3},
{-SQRT3_3,-SQRT3_3,SQRT3_3},{SQRT3_3,-SQRT3_3,SQRT3_3}};

and now it does not generates an error. Nonetheless, it generates an warning:
/media/34GB/demos/asmfrt/BVolume.h|19|warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x|

Shall I concern myself with it?

[mbozzi]

You should update your compiler.

You are using a version of C++ standardized in 1998. C++ has changed a lot in the past 22 years.

[colt]

Ops, I talked to early, I am now receiving: /media/34GB/demos/asmfrt/Vec3f.h|32|undefined reference to `BVolume::normals'| . I tried to add -std=c++0x, but it appears to generate a compiler bug in file "vector.tcc"

/usr/include/c++/4.4/bits/vector.tcc|314|error: no match for ‘operator=’ in ‘__position.__gnu_cxx::__normal_iterator<_Iterator, _Container>::operator* [with _Iterator = Bbox*, _Container = std::vector<Bbox, std::allocator<Bbox> >]() = ((const Bbox&)((const Bbox*)std::forward [with _Tp = const Bbox&](((const Bbox&)((const Bbox*)__args#0)))))’|

refering to line *__position = _Tp(std::forward<_Args>(__args)...);

About update the compiler, unfortunately I cannot do that.

[Thomas1965]

What compiler do you use?
Does it have to be inside the class?
Otherwise you could define a global constant.

[seeplus]

class Vec3f {
public:
	inline Vec3f() : x(0), y(0), z(0) {}
	inline Vec3f(const float xx, const float yy, const float zz) : x(xx), y(yy), z(zz) { }

	float x, y, z;
};

class BVolume {
public:
	BVolume() {}
private:
	//Vec2f slabs[8];
	static const Vec3f normals[8];
	int min_triangle, max_triangle;
};

const Vec3f BVolume::normals[8] = {{1,0,0},{0,1,0},{1,0,0},{0,1,0},{1,0,0},{0,1,0},{1,0,0},{0,1,0}};

compiles Ok using VS.

About update the compiler, unfortunately I cannot do that.

What version are you using? If looks like you're using gcc which is free. The current version is 10.2 I really recommend that you update to the latest compiler version.

[colt]

Yes, I found a solution just like you described seeplus. However, I am now facing "/media/34GB/demos/asmfrt/Vec3f.h|11|multiple definition of `BVolume::normals'|"

obj/Debug/RayTracer.o:/media/34GB/demos/asmfrt/RayTracer.cpp|376|first defined here|

This happens many times. How can I solve it?

[coder777]

[EDIT] misinterpreted
That is most likely due to the lack of include guards. See:

https://en.wikipedia.org/wiki/Include_guard

I.e. you should surround your header code like so:

#ifndef INCLUDEGUARD_...
#define INCLUDEGUARD_...

...

#endif 

Also you may use #pragma once which is supported by most compiler.

[colt]

Yes, I actually have them:

#ifndef BVOLUME_H_INCLUDED
#define BVOLUME_H_INCLUDED 

#endif

Any suggestions?