Thread: Multiple definition issue when using static const

  1. #1
    Registered User
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    Sep 2019
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    Multiple definition issue when using static const

    Hello, I defined this as a private member of my class:

    Code:
    static const Vec3f normals [7];
    and then try to initialize it outside the class:

    Code:
    const Vec3f BVolume::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}};
    This in a header file. When trying to compile it, I receive three error messages like
    Code:
    /media/34GB/demos/asmfrt/TextManager.cpp|352|multiple definition of `BVolume::normals'|
    Two of them at the end of classes. How it cn be solved?

  2. #2
    C++ Witch laserlight's Avatar
    Join Date
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    Two options come to mind:
    • Declare normals in the class definition (which is what you're already doing) then define and initialise it in exactly one source file rather than in the header (i.e., move it from the header to exactly one source file).
    • Declare normals with constexpr and define and initialise it in the class definition:
      Code:
      static constexpr 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}};
      Of course, I'm assuming that SQRT3_3 can be used in a constexpr context, e.g., it is itself a constexpr, a const initialised at compile time, an enum, a macro constant.
    Last edited by laserlight; 09-14-2020 at 04:35 PM.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
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