CODEWITHSUNDEEP
gccstructunion
areslp
areslp

Reputation: 473

Anonymous structs issues in union

I have something like this:

union MyBBox3D
{
    struct
    {
        float  m_fBox[6]; 
        float  m_fCenter[3];
        float  m_fDiagonalLen;
        float  m_fNormalizeFactor;
        float  m_fScaling[3];
    };
    struct
    {
        float  m_fMin[3];
        float  m_fMax[3];
        float  m_fCenter[3]; 
        float  m_fDiagonalLen;
        float  m_fNormalizeFactor;
        float  m_fScaling[3];
    };
    struct
    {
        float  m_fMinX, m_fMinY, m_fMinZ;
        float  m_fMaxX, m_fMaxY, m_fMaxZ;
        float  m_fCenterX, m_fCenterY, m_fCenterZ;
        float  m_fDiagonalLen;
        float  m_fNormalizeFactor;
        float  m_fScalingX, m_fScalingY, m_fScalingZ;
    };
};

It compiles well with vs2008 and intel compiler 12.0, but cant be compiled with gcc4.6.3, it gives the following errors:

In file included from Mesh/MyMeshTool.cpp:17:0:
Mesh/MyMeshTool.h:68:28: error: declaration of ‘float                   nsMeshLib::MyBBox3D::<anonymous struct>::m_fCenter [3]’
Mesh/MyMeshTool.h:59:28: error: conflicts with previous declaration ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fCenter [3]’
Mesh/MyMeshTool.h:69:17: error: declaration of ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fDiagonalLen’
Mesh/MyMeshTool.h:60:17: error: conflicts with previous declaration ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fDiagonalLen’
Mesh/MyMeshTool.h:70:20: error: declaration of ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fNormalizeFactor’
Mesh/MyMeshTool.h:61:20: error: conflicts with previous declaration ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fNormalizeFactor’
Mesh/MyMeshTool.h:71:32: error: declaration of ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fScaling [3]’
Mesh/MyMeshTool.h:62:32: error: conflicts with previous declaration ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fScaling [3]’
Mesh/MyMeshTool.h:78:17: error: declaration of ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fDiagonalLen’
Mesh/MyMeshTool.h:60:17: error: conflicts with previous declaration ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fDiagonalLen’
Mesh/MyMeshTool.h:79:20: error: declaration of ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fNormalizeFactor’
Mesh/MyMeshTool.h:61:20: error: conflicts with previous declaration ‘float nsMeshLib::MyBBox3D::<anonymous struct>::m_fNormalizeFactor’

How can I solve this problem? Thanks in advance!

Upvotes: 1

Views: 1282

Answers (2)

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

Recent GCC do accept unamed fields if you pass the -fms-extensions program option to gcc invocation, but this is an extension do the standard C99 specification.

You could also use preprocessor tricks with care, e.g.

union myunion {
  struct {
     int fa_u1;
     int fb_u1;
  } u1;
#define fa u1.fa_u1
#define fb u1.fb_u1
  struct {
     double fc_u2;
     char fd_u2[8];
  } u2;
#define fc u2.fc_u2
#define fd u2.fd_u2
}

Then you can code x.fa instead of x.u1.fa_u1 etc. Use preprocessor tricks with care and caution (remember that a #define has full translation unit scope). In practice you'll want the fa, u1, fa_u1 names to be long and unique.

Upvotes: 0

paxdiablo
paxdiablo

Reputation: 882596

I think in this case (where the separate structures making up the union share identifier names), you're probably better off not using anonymous structures.

Either that or make the names unique across the entire union.

Anything else is just asking for trouble :-)

Upvotes: 1

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