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  Keyword:  union
 
  Syntax:   union [tag] {member-declaration-list} [declarators];
            union tag declarators;
 
  Summary:  Declares a union type and/or a union variable.
 
     If braces are given, the union declares a union type consisting of
     a sequence of variable values (known as members of the union) that
     can have different types. A variable of a union type can hold one
     member of any type defined by the union. The size of the union is
     the size of the largest type in the union. Variables can be
     defined by listing their names after the closing brace.
 
     If braces are not given, the union keyword is used to define a
     union variable. The tag identifies the type. For example,
 
          union UNKNOWN         // Declare UNKNOWN union type
          {
             char   ch;         // Members of different types
             int    i;
             long   l;
             float  f;
             double d;
          } var1;               // Variable of type UNKNOWN
          union UNKNOWN var2;   // Variable of type UNKNOWN
          var1.i = 6;           // Use variable as integer
          var2.d = 5.327;       // Use variable as double
 
     A non-ANSI extension allows unions to be defined without
     declarators when they are members of another struct or a union.
     This allows the members to be referenced as if they were declared
     directly in the containing struct or union. For example,
 
          struct example
          {
             int a,b;
             union {
                     char  str[4];
                     long  l;
                     float f;
                   };
             char name[10];
          } Example;
 
          Example.l = 305;
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