CHAPTER 9 : Data Usage

PART 4 : USAGE

CHAPTER 9 : Data Usage
9.1 Declarations
9.2 Using floating point numbers
9.3 Using 'typedef'
9.4 Using global data
9.5 Using Structures
9.6 Using Unions
9.7 Using Arrays
9.8 Using Pointers
9.9 Using bit structures
9.10 Using Constants
9.11 Using 'static' declarations
9.12 Initializing variables
9.13 Summary

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9.6  Using Unions

Unions, by definition, operate at the hardware level, where they can be very useful where it is necessary to map an item in alternative ways. For example, where a 16-bit register may also be addressed as two individual 8-bit registers:

union HL_REGISTER
{
    int     Reg16;
    struct
    {
        char    LowReg8;
        char    HighReg8;
    } HiLo;
};

Unions are often non-portable, and should thus be used only where necessary, in isolated, implementation-specific parts of the code.

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