Question

I have a block of code that i’m trying to covert from an old qt file into C# but i’m a little unclear what is going on in the struct within the union below. I’m not sure what the ‘:’ does… i’m guessing it sets the size but could not find any documentation on this. Also since C# does not have unions what is the best practice for converting something like this. Thank you

union uAWord
{
   uAWord()
     : m_AWord(0) {}

    struct sBcdAWord
    {
      quint32 m_O  :8;
      quint32 m_S  :2;
      quint32 m_D  :18;
      quint32 m_SS :3;
      quint32 m_P  :1;
    }
    sBcdAWord m_F;
    quint32 m_AWord;
}

Answer 1

This is what is called BitFields. the portion sBcdWord is a 32 bit word, and each field is a portion of that word taking respectively 8,2,18,3,1 BIT:
So the word layout is as below:

• Bit0-Bit7 m_0
• Bit8-Bit9 m_S
• Bit10-Bit27 m_D
• Bit28-Bit30 m_ss
• Bit31 m_P

How to port this in C# depends if you are convettually porting the code, or if you need to PInvoke. In the case of PInvoke the best solution is probably to map sBcdAWord as an Unit32, and create some accessor strategy to mask on reading writing. If it is a code port, use separeted properties would be good unless there is special needing in memory usage saving.