C++ Enumeration

An enumeration is a user-defined data type that consists of integral constants. To define an enumeration, keyword enum is used.

 enum season { spring, summer, autumn, winter };

Here, the name of the enumeration is season.

And, spring, summer and winter are values of type season.

By default, spring is 0, summer is 1 and so on. You can change the default value of an enum element during declaration (if necessary).

 enum season { spring = 0, summer = 4, autumn = 8, winter = 12 };

Enumerated Type Declaration

When you create an enumerated type, only a blueprint for the variable is created. Here's how you can create variables of enum type.

 enum boolean { false, true }; // inside function enum boolean check;

Here, a variable check of type enum boolean is created.

Here is another way to declare the same check variable using different syntax.

 enum boolean { false, true } check;

Example: Enumeration Type

 #include <iostream> using namespace std; enum week { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday }; int main() { week today; today = Wednesday; cout << "Day " << today+1; return 0; }

Output

 Day 4

Example: Changing Default Value of Enums

 #include <iostream> using namespace std; enum seasons { spring = 34, summer = 4, autumn = 9, winter = 32}; int main() { seasons s; s = summer; cout << "Summer = " << s << endl; return 0; }

Output

 Summer = 4

Why are enums used in C++ programming?

An enum variable takes only one value out of many possible values. Let us look at an example.

 #include <iostream> using namespace std; enum suit { club = 0, diamonds = 10, hearts = 20, spades = 3 } card; int main() { card = club; cout << "Size of enum variable " << sizeof(card) << " bytes."; return 0; }

Output

 Size of enum variable 4 bytes.

It's because the size of an integer is 4 bytes. This makes enum a good choice to work with flags.

You can accomplish the same task using C++ structures. However, working with enums gives you efficiency along with flexibility.

How to use enums for flags?

Let us look at an example.

 enum designFlags {	ITALICS = 1,	BOLD = 2,	UNDERLINE = 4 } button;

Suppose you are designing a button for a Windows application. You can set flags ITALICS, BOLD and UNDERLINE to work with text.

There is a reason why all the integral constants are powers of 2 in the above pseudocode.

 // In binary ITALICS = 00000001 BOLD = 00000010 UNDERLINE = 00000100 

Since, the integral constants are power of 2, you can combine two or more flags at once without overlapping using bitwise OR | operator. This allows you to choose two or more flags at once. For example,

 #include <iostream> using namespace std; enum designFlags { ITALICS = 1, BOLD = 2, UNDERLINE = 4 }; int main() { int myDesign = BOLD | UNDERLINE; // 00000010 // | 00000100 // ___________ // 00000110 cout << myDesign; return 0; }

Output

 6

When the output is 6, you always know that BOLD and UNDERLINE are used.

Also, you can add flags to your requirements.

 if (myDesign & ITALICS) { // code for italics }

Here, we have added italics to our design. Note, only code for italics is written inside the if statement.

You can accomplish almost anything in C++ programming without using enumerations. However, they can be pretty handy in certain situations. That's what differentiates good programmers from great programmers.