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Annotation of coherent/a/usr/man/ALL/union, revision 1.1.1.1

1.1       root        1: 
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                      3: union                       C Keyword                       union
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                      7: 
                      8: Multiply declare a variable
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                     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;
                     24: 
                     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 *****
                     40: 
                     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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