C++ Basic Enumeration Declaration


Example

Standard enumerations allow users to declare a useful name for a set of integers. The names are collectively referred to as enumerators. An enumeration and its associated enumerators are defined as follows:

enum myEnum
{
    enumName1,
    enumName2,
};

An enumeration is a type, one which is distinct from all other types. In this case, the name of this type is myEnum. Objects of this type are expected to assume the value of an enumerator within the enumeration.

The enumerators declared within the enumeration are constant values of the type of the enumeration. Though the enumerators are declared within the type, the scope operator :: is not needed to access the name. So the name of the first enumerator is enumName1.

C++11

The scope operator can be optionally used to access an enumerator within an enumeration. So enumName1 can also be spelled myEnum::enumName1.

Enumerators are assigned integer values starting from 0 and increasing by 1 for each enumerator in an enumeration. So in the above case, enumName1 has the value 0, while enumName2 has the value 1.

Enumerators can also be assigned a specific value by the user; this value must be an integral constant expression. Enumerators who's values are not explicitly provided will have their value set to the value of the previous enumerator + 1.

enum myEnum
{
    enumName1 = 1, // value will be 1
    enumName2 = 2, // value will be 2
    enumName3,     // value will be 3, previous value + 1
    enumName4 = 7, // value will be 7
    enumName5,     // value will be 8
    enumName6 = 5, // value will be 5, legal to go backwards
    enumName7 = 3, // value will be 3, legal to reuse numbers
    enumName8 = enumName4 + 2, // value will be 9, legal to take prior enums and adjust them
};