Class: CRC32 in Category General VBA/VB6 : Data Integrity from Total Visual SourceBook

Calculate the 32-bit Cyclic Redundancy Check (CRC) of a file or string; can also be used for Checksum in VBA and VB6.

Procedure Name Type Description
(Declarations) Declarations Declarations and private variables for the CCRC32 class.
InputFileName Property Get the name of the input file.
GetCRCFromFile Method Generate a CRC for the file specified in the InputFile property.
GetCRCFromString Method Generate a CRC for a string using the Unicode version of this method. For an ASCII version, see GetCRCFromStringAscii.
GetCRCFromStringAscii Method Generate a CRC for a string using the ASCII version of this method. For the Unicode version, use GetCRCFromString.
ConstructCRCTable Private Fill the CRC table with precalculated values. This is more efficient than calculating CRC's each time they are needed.
ReadFile Private Read the specified number of bytes from the file which significantly increases the speed of processing files. The alternative to using a file buffer is reading a byte at a time from the file.
UpdateCRC32 Private Calculate the new CRC based on the current CRC and the byte value.
' Example of CCRC32 to calculate the 32-bit CRC of a file or string
' To try this example, do the following:
' 1. Create a new user form
' 2. Create a command button named 'cmdTest'
' 3. Paste all the code from this example to the new form's module.
' 4. Run the form

' This example assumes that the sample files are located in the folder named by the following constant.
Private Const mcstrSamplePath As String = "C:\TVSBSamp"

' By defining the class WithEvents, you can capture the Progress event to display information to your user.
' To use events, this module must be a class or form/report. If you don't want to capture the Progress event, you can use a regular module.
Private WithEvents mclsCRC32 As CCRC32

Private Sub cmdTest_Click()
  ' Comments: Examples of converting files and strings to a 32-bit Cyclic Redundancy Check (CRC) value; can also be used for Checksum

  Dim lngCRCValue As Long
  Dim strString As String

  ' Initialize class
  Set mclsCRC32 = New CCRC32

  ' Example of creating a 32-bit CRC value for a file
  mclsCRC32.InputFileName = mcstrSamplePath & "\sample.mdb"
  lngCRCValue = mclsCRC32.GetCRCFromFile()

  MsgBox "CRC File Value:" & lngCRCValue

  ' Example of creating a 32-bit CRC value for a string
  strString = "One small step for [a] man; one giant leap for mankind"
  lngCRCValue = mclsCRC32.GetCRCFromString(strString)

  MsgBox "String CRC Value: " & lngCRCValue

  ' Close class
  Set mclsCRC32 = Nothing

End Sub

Private Sub mclsCRC32_Progress(dblPercentage As Double)
  ' Comments: This procedure captures the Progress Event and reveals the percentage completion for the file that's being compressed
  '           This example puts the information on the Immediate Window. You could show the information on a form as text or display a graphic.
  ' Params  : dblPercentage       Percent of completion between 0 and 1

  Debug.Print "Percent done: " & Format$(dblPercentage, "Percent")
End Sub

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