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Annotation of coherent/a/usr/man/ALL/union, revision 1.1

1.1     ! root        1: 
        !             2: 
        !             3: union                       C Keyword                       union
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        !             8: Multiply declare a variable
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        !            10: 
        !            11: A union  defines an area  of storage that  can accept any  one of
        !            12: several types  of data.  In effect, it  is a multiple declaration
        !            13: of a  variable.  For example, a union may  be declared to consist
        !            14: of  an int,  a double,  and  a char  *.  Any  one of  these three
        !            15: elements can be held by the  union at a time, and will be handled
        !            16: appropriately by it.  For example, the declaration
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        !            18: 
        !            19: union {
        !            20:         int number;
        !            21:         double bignumber;
        !            22:         char *stringptr;
        !            23: } example;
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        !            25: 
        !            26: allows example to hold either an iinntt, a ddoouubbllee, or a pointer to a
        !            27: cchhaarr, whichever  is needed  at the time.   All of these  have the
        !            28: same address.  The elements of a uunniioonn are accessed like those of
        !            29: a ssttrruucctt:  for example, to access nnuummbbeerr  from the above example,
        !            30: type eexxaammppllee.nnuummbbeerr.
        !            31: 
        !            32: unions are helpful in dealing with heterogeneous data, especially
        !            33: within structures; however, you are responsible for keeping track
        !            34: of what data  type the union is holding at  any given time.  Pas-
        !            35: sing a double to a union  and then reading the union as though it
        !            36: held  an  int  will yield  results  that  are unpredictable,  and
        !            37: probably unwelcome.
        !            38: 
        !            39: ***** Example *****
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        !            41: For an example of how to  use a union in a program, see the entry
        !            42: for byte ordering.
        !            43: 
        !            44: ***** See Also *****
        !            45: 
        !            46: C keywords, struct, structure
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        !            64: COHERENT Lexicon                                           Page 1
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