Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

 ◄Example►                                   ◄Up► ◄Contents► ◄Index► ◄Back►
─────C/C++ Language─────────────────────────────────────────────────────────
 
  Keyword:  union
 
  Syntax:   union [tag] {member-list} [declarators];
            [union] tag declarators;
 
  Summary:  Declares a union type and/or a variable of a union type.
            See: ◄Anonymous Unions►
 
  See also: class, struct
 
     A union is a user-defined data type that can hold values of
     different types at different times. It is similar to a structure
     except that all of its members start at the same location in
     memory. A union variable can contain only one of its members
     at a time. The size of the union is at least the size of the
     largest member.
 
     A C++ union is a limited form of the class type. It can contain
     access specifiers (public, protected, private), member data,
     and member functions, including constructors, and destructors.
     It cannot contain virtual functions or static data members.
     It cannot be used as a base class, nor can it have base classes.
     Default access of members in a union is public.
 
     A C union type can contain only data members.
 
     Declaring a Union
 
     Begin the declaration of a union with the union keyword, and
     enclose the member list in curly braces:
 
          union UNKNOWN    // Declare union type
          {
             char   ch;
             int    i;
             long   l;
             float  f;
             double d;
          } var1;          // Optional declaration of union variable
 
     In C, you must use the union keyword to declare a union variable.
     In C++, the union keyword is unnecessary:
 
          union UNKNOWN var2;   // C declaration of a union variable
          UNKNOWN var3;         // C++ declaration of a union variable
 
     Using a Union
 
     A variable of a union type can hold one value of any type
     declared in the union. Use the dot operator (.) to access a
     member of a union:
 
          var1.i = 6;           // Use variable as integer
          var2.d = 5.327;       // Use variable as double
                                    -♦-