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Enumeration and C++

Enumerated types are user-defined types whose variables can have a particular set of integer values. The type can be named, as in

enum WeekendDay {Saturday, Sunday};

(after which constants Saturday and Sunday can be used in place of 0 and 1, and variables of type WeekendDay can be created) or unnamed, as in

enum {Sat, Sun};

after which the constants Sat and Sun can be used in place of 0 and 1. By default the values start at 0 and then increment by 1, but that can be overridden. For example, in

enum {Mon=3, Tue, Wed=2, Thu};

Mon is 3, Tue is 4, Wed is 2 and Thu is 3 (note that the values needn't be unique).

They can be used where integer-like values are required, so the following works

int i=Sat;

but conversion doesn't work the other way - the following doesn't compile

WeekendDay w=1;

You need to do

WeekendDay w=static_cast<WeekendDay>(1);


Though enumerations can make code more readable, they're less useful for making code more robust.

  • It's possible to variables of enumerated types to values outside their allowed range. Compilers won't complain about the following
    WeekendDay w=static_cast<WeekendDay>(99);
    (though the result's undefined)
  • Though you can't set an enumerated variable to an integer, you can set it to an unrelated enumerated value. The following isn't illegal
    int main() { enum WeekendDay {Saturday, Sunday}; enum Fruit {Apple, Orange, Pear}; WeekendDay w; Fruit f=Pear; w=Orange; w=f; }
  • If you print such a variable, you'll get an integer, not a useful string like Saturday