C++ Notes: Enum Values and I/O

Setting enum values

It's possible to control the values that are assigned to each enum constant. If a value is assingned to a constant, each successive constant without a value is assigned a value one greater than the previous.
enum Day {MON=1, TUE, WED, THU, FRI, SAT, SUN};
The value of MON is one, TUE is two, etc instead of starting at zero.

Another use of specific values is to create sets. Explicitly setting the values to powers of two represents each as separate bit. These values can then manipulated using the bit operations (&, |, ^ and ~).

enum Day {MON=1, TUE=2, WED=4, THU=8, FRI=16, SAT=32, SUN=64};
. . .
Day today;  // This will have one of the values in it.
. . .
if ((today & WEEKDAY) != 0) . . .

Enum I/O

I/O of enums uses their integer values, not their names. This is not what is desired normally, so extra programming is required on input and output to use the names instead of integer values. The extra work for enum I/O means that they are often not used for simple programs.

Other languages

Java will have type-safe enums in version 1.5. Currently it requires programmers to explicitly declare each name as a constant ints.

C# provides enums with additional facilities, eg to get names and check values.

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