Flags attribute and bitwise enums in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the [Flags] attribute in C# enums?

The [Flags] attribute allows an enum to represent a combination of values using bitwise operations, making it easier to work with sets of options.

beginner

How do you define an enum with bitwise flags in C#?

Define enum members with values as powers of two (1, 2, 4, 8, etc.) so each bit represents a unique flag. Example: [Flags] enum MyFlags { None = 0, Read = 1, Write = 2, Execute = 4 }

beginner

How can you check if a specific flag is set in a bitwise enum variable?

Use the bitwise AND operator (&) to check if the flag is set. For example, (myFlags & MyFlags.Read) == MyFlags.Read means the Read flag is set.

beginner

What does combining flags with the bitwise OR operator (|) do?

It creates a new value that contains all the flags combined. For example, MyFlags.Read | MyFlags.Write combines both Read and Write flags.

beginner

Why should enum values for flags be powers of two?

Because powers of two set unique bits in binary, allowing flags to be combined and checked without overlap or confusion.

What does the [Flags] attribute do in a C# enum?

A Allows combining enum values using bitwise operations

B Makes enum values readonly

C Changes enum to string values

D Prevents enum from being used in switch statements

The [Flags] attribute enables combining enum values using bitwise operations to represent multiple options.

Which of these is a correct value for a bitwise flag enum member?

A 3

B 5

C 8

D 7

8 is a power of two (2^3), suitable for a unique bit flag. Values like 3, 5, 7 are combinations, not single flags.

How do you check if the Write flag is set in a variable 'flags' of a bitwise enum?

A flags + Write

B flags == Write

C flags | Write

D (flags & Write) == Write

Using bitwise AND (&) and comparing to the flag checks if that flag is set.

What is the result of combining Read (1) and Execute (4) flags using bitwise OR?

A 7

B 5

C 3

D 0

1 | 4 equals 5 in binary, combining Read and Execute flags.

Why is it important to assign powers of two to enum flags?

A To allow unique bits for each flag

B To make enums smaller in memory

C To sort enum values alphabetically

D To prevent enum from being changed

Powers of two ensure each flag uses a unique bit, enabling proper combination and checking.

Explain how the [Flags] attribute and bitwise enums work together in C#.

Think about how bits represent options and how you combine or check them.

Describe how to define and use a bitwise enum to represent multiple permissions like Read, Write, and Execute.

Imagine permissions as switches you can turn on or off.