Managing Bit Flags (Part 1)

by ps1Mar 3, 2017

Occasionally, you might have to deal with bit flag values. Each bit in a number represents a certain setting, and your code might need to determine whether a given flag is set, or set a given flag without tampering with the other bits.

This typically involves a lot of fiddling with binary operators. In PowerShell 5, however, there is a much easier approach, thanks to the support for flag enumerations.

Let’s assume you have a value like 56823 and would like to know which bits are set. You could convert the number to visualize the bits:

 
PS C:\> [Convert]::ToString(56823, 2)
1101110111110111

If you know the meaning of each bit, a much more powerful way is to define an enumeration:

#requires -Version 5
 
[flags()] 
enum CustomBitFlags
{
    None    = 0
    Option1 = 1
    Option2 = 2
    Option3 = 4
    Option4 = 8
    Option5 = 16
    Option6 = 32
    Option7 = 64
    Option8 = 128
    Option9 = 256
    Option10= 512
    Option11= 1024
    Option12= 2048
    Option13= 4096
    Option14= 8192
    Option15= 16384
    Option16= 32768
    Option17= 65536
}

For each bit, provide a friendly name, and make sure you add the attribute [Flags] (which allows multiple values to be set).

Now it’s super easy to decipher the decimal – simply convert it into your new enum type:

$rawflags = 56823
[CustomBitFlags]$flags = $rawflags

This is what you get:

 
PS C:\> $flags
Option1, Option2, Option3, Option5, Option6, Option7, Option8, Option9, Option11, Option12, Option13, Option15, Option16

And if you just wanted to check whether or not a given flag was set, use the method HasFlag():

 
PS C:\> $flags.HasFlag([CustomBitFlags]::Option1)

True

PS C:\> $flags.HasFlag([CustomBitFlags]::Option4)

False

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Managing Bit Flags (Part 1)

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