# Reading 2GB+ files in binary in VBA and File Hashes

There is a built in easy way to read files in binary within VBA, however it has a restriction of 2GB (2,147,483,647 bytes - max of Long data type). As technology evolves, this 2GB limit is easily breached. e.g. an ISO image of Operating System install DVD disc. Microsoft does provide a way to overcome this via low level Windows API and here is a backup of it.

Also demonstrate (Read part) for calculating File Hashes without external program like fciv.exe from Microsoft.

# This have to be in a Class module, examples later referred as "Random"

' How To Seek Past VBA's 2GB File Limit
' Source: https://support.microsoft.com/en-us/kb/189981 (Archived)
' This must be in a Class Module

Option Explicit

Public Enum W32F_Errors
    W32F_UNKNOWN_ERROR = 45600
    W32F_FILE_ALREADY_OPEN
    W32F_PROBLEM_OPENING_FILE
    W32F_FILE_ALREADY_CLOSED
    W32F_Problem_seeking
End Enum

Private Const W32F_SOURCE = "Win32File Object"
Private Const GENERIC_WRITE = &H40000000
Private Const GENERIC_READ = &H80000000
Private Const FILE_ATTRIBUTE_NORMAL = &H80
Private Const CREATE_ALWAYS = 2
Private Const OPEN_ALWAYS = 4
Private Const INVALID_HANDLE_VALUE = -1

Private Const FILE_BEGIN = 0, FILE_CURRENT = 1, FILE_END = 2

Private Const FORMAT_MESSAGE_FROM_SYSTEM = &H1000

Private Declare Function FormatMessage Lib "kernel32" Alias "FormatMessageA" ( _
    ByVal dwFlags As Long, _
    lpSource As Long, _
    ByVal dwMessageId As Long, _
    ByVal dwLanguageId As Long, _
    ByVal lpBuffer As String, _
    ByVal nSize As Long, _
    Arguments As Any) As Long

Private Declare Function ReadFile Lib "kernel32" ( _
    ByVal hFile As Long, _
    lpBuffer As Any, _
    ByVal nNumberOfBytesToRead As Long, _
    lpNumberOfBytesRead As Long, _
    ByVal lpOverlapped As Long) As Long

Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Declare Function WriteFile Lib "kernel32" ( _
    ByVal hFile As Long, _
    lpBuffer As Any, _
    ByVal nNumberOfBytesToWrite As Long, _
    lpNumberOfBytesWritten As Long, _
    ByVal lpOverlapped As Long) As Long

Private Declare Function CreateFile Lib "kernel32" Alias "CreateFileA" ( _
    ByVal lpFileName As String, _
    ByVal dwDesiredAccess As Long, _
    ByVal dwShareMode As Long, _
    ByVal lpSecurityAttributes As Long, _
    ByVal dwCreationDisposition As Long, _
    ByVal dwFlagsAndAttributes As Long, _
    ByVal hTemplateFile As Long) As Long

Private Declare Function SetFilePointer Lib "kernel32" ( _
    ByVal hFile As Long, _
    ByVal lDistanceToMove As Long, _
    lpDistanceToMoveHigh As Long, _
    ByVal dwMoveMethod As Long) As Long

Private Declare Function FlushFileBuffers Lib "kernel32" (ByVal hFile As Long) As Long

Private hFile As Long, sFName As String, fAutoFlush As Boolean

Public Property Get FileHandle() As Long
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    FileHandle = hFile
End Property

Public Property Get FileName() As String
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    FileName = sFName
End Property

Public Property Get IsOpen() As Boolean
    IsOpen = hFile <> INVALID_HANDLE_VALUE
End Property

Public Property Get AutoFlush() As Boolean
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    AutoFlush = fAutoFlush
End Property

Public Property Let AutoFlush(ByVal NewVal As Boolean)
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    fAutoFlush = NewVal
End Property

Public Sub OpenFile(ByVal sFileName As String)
    If hFile <> INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_OPEN, sFName
    End If
    hFile = CreateFile(sFileName, GENERIC_WRITE Or GENERIC_READ, 0, 0, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, 0)
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_PROBLEM_OPENING_FILE, sFileName
    End If
    sFName = sFileName
End Sub

Public Sub CloseFile()
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    CloseHandle hFile
    sFName = ""
    fAutoFlush = False
    hFile = INVALID_HANDLE_VALUE
End Sub

Public Function ReadBytes(ByVal ByteCount As Long) As Variant
    Dim BytesRead As Long, Bytes() As Byte
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    ReDim Bytes(0 To ByteCount - 1) As Byte
    ReadFile hFile, Bytes(0), ByteCount, BytesRead, 0
    ReadBytes = Bytes
End Function

Public Sub WriteBytes(DataBytes() As Byte)
    Dim fSuccess As Long, BytesToWrite As Long, BytesWritten As Long
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    BytesToWrite = UBound(DataBytes) - LBound(DataBytes) + 1
    fSuccess = WriteFile(hFile, DataBytes(LBound(DataBytes)), BytesToWrite, BytesWritten, 0)
    If fAutoFlush Then Flush
End Sub

Public Sub Flush()
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    FlushFileBuffers hFile
End Sub

Public Sub SeekAbsolute(ByVal HighPos As Long, ByVal LowPos As Long)
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    LowPos = SetFilePointer(hFile, LowPos, HighPos, FILE_BEGIN)
End Sub

Public Sub SeekRelative(ByVal Offset As Long)
    Dim TempLow As Long, TempErr As Long
    If hFile = INVALID_HANDLE_VALUE Then
        RaiseError W32F_FILE_ALREADY_CLOSED
    End If
    TempLow = SetFilePointer(hFile, Offset, ByVal 0&, FILE_CURRENT)
    If TempLow = -1 Then
        TempErr = Err.LastDllError
        If TempErr Then
            RaiseError W32F_Problem_seeking, "Error " & TempErr & "." & vbCrLf & CStr(TempErr)
        End If
    End If
End Sub

Private Sub Class_Initialize()
    hFile = INVALID_HANDLE_VALUE
End Sub

Private Sub Class_Terminate()
    If hFile <> INVALID_HANDLE_VALUE Then CloseHandle hFile
End Sub

Private Sub RaiseError(ByVal ErrorCode As W32F_Errors, Optional sExtra)
    Dim Win32Err As Long, Win32Text As String
    Win32Err = Err.LastDllError
    If Win32Err Then
        Win32Text = vbCrLf & "Error " & Win32Err & vbCrLf & _
        DecodeAPIErrors(Win32Err)
    End If
    Select Case ErrorCode
        Case W32F_FILE_ALREADY_OPEN
            Err.Raise W32F_FILE_ALREADY_OPEN, W32F_SOURCE, "The file '" & sExtra & "' is already open." & Win32Text
        Case W32F_PROBLEM_OPENING_FILE
            Err.Raise W32F_PROBLEM_OPENING_FILE, W32F_SOURCE, "Error opening '" & sExtra & "'." & Win32Text
        Case W32F_FILE_ALREADY_CLOSED
            Err.Raise W32F_FILE_ALREADY_CLOSED, W32F_SOURCE, "There is no open file."
        Case W32F_Problem_seeking
            Err.Raise W32F_Problem_seeking, W32F_SOURCE, "Seek Error." & vbCrLf & sExtra
        Case Else
            Err.Raise W32F_UNKNOWN_ERROR, W32F_SOURCE, "Unknown error." & Win32Text
    End Select
End Sub

Private Function DecodeAPIErrors(ByVal ErrorCode As Long) As String
    Dim sMessage As String, MessageLength As Long
    sMessage = Space$(256)
    MessageLength = FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM, 0&, ErrorCode, 0&, sMessage, 256&, 0&)
    If MessageLength > 0 Then
        DecodeAPIErrors = Left(sMessage, MessageLength)
    Else
        DecodeAPIErrors = "Unknown Error."
    End If
End Function

# Code for Calculating File Hash in a Standard module

Private Const HashTypeMD5 As String = "MD5" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.md5cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA1 As String = "SHA1" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha1cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA256 As String = "SHA256" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha256cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA384 As String = "SHA384" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha384cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA512 As String = "SHA512" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha512cryptoserviceprovider(v=vs.110).aspx

Private uFileSize As Double ' Comment out if not testing performance by FileHashes()

Sub FileHashes()
    Dim tStart As Date, tFinish As Date, sHash As String, aTestFiles As Variant, oTestFile As Variant, aBlockSizes As Variant, oBlockSize As Variant
    Dim BLOCKSIZE As Double
    
    ' This performs performance testing on different file sizes and block sizes
    aBlockSizes = Array("2^12-1", "2^13-1", "2^14-1", "2^15-1", "2^16-1", "2^17-1", "2^18-1", "2^19-1", "2^20-1", "2^21-1", "2^22-1", "2^23-1", "2^24-1", "2^25-1", "2^26-1")
    aTestFiles = Array("C:\ISO\clonezilla-live-2.2.2-37-amd64.iso", "C:\ISO\HPIP201.2014_0902.29.iso", "C:\ISO\SW_DVD5_Windows_Vista_Business_W32_32BIT_English.ISO", "C:\ISO\Win10_1607_English_x64.iso", "C:\ISO\SW_DVD9_Windows_Svr_Std_and_DataCtr_2012_R2_64Bit_English.ISO")
    Debug.Print "Test files: " & Join(aTestFiles, " | ")
    Debug.Print "BlockSizes: " & Join(aBlockSizes, " | ")
    For Each oTestFile In aTestFiles
        Debug.Print oTestFile
        For Each oBlockSize In aBlockSizes
            BLOCKSIZE = Evaluate(oBlockSize)
            tStart = Now
            sHash = GetFileHash(CStr(oTestFile), BLOCKSIZE, HashTypeMD5)
            tFinish = Now
            Debug.Print sHash, uFileSize, Format(tFinish - tStart, "hh:mm:ss"), oBlockSize & " (" & BLOCKSIZE & ")"
        Next
    Next
End Sub

Private Function GetFileHash(ByVal sFile As String, ByVal uBlockSize As Double, ByVal sHashType As String) As String
    Dim oFSO As Object ' "Scripting.FileSystemObject"
    Dim oCSP As Object ' One of the "CryptoServiceProvider"
    Dim oRnd As Random ' "Random" Class by Microsoft, must be in the same file
    Dim uBytesRead As Double, uBytesToRead As Double, bDone As Boolean
    Dim aBlock() As Byte, aBytes As Variant ' Arrays to store bytes
    Dim aHash() As Byte, sHash As String, i As Long
    'Dim uFileSize As Double ' Un-Comment if GetFileHash() is to be used individually
    
    Set oRnd = New Random ' Class by Microsoft: Random
    Set oFSO = CreateObject("Scripting.FileSystemObject")
    Set oCSP = CreateObject("System.Security.Cryptography." & sHashType & "CryptoServiceProvider")
    
    If oFSO Is Nothing Or oRnd Is Nothing Or oCSP Is Nothing Then
        MsgBox "One or more required objects cannot be created"
        GoTo CleanUp
    End If
    
    uFileSize = oFSO.GetFile(sFile).Size ' FILELEN() has 2GB max!
    uBytesRead = 0
    bDone = False
    sHash = String(oCSP.HashSize / 4, "0") ' Each hexadecimal has 4 bits
    
    Application.ScreenUpdating = False
    ' Process the file in chunks of uBlockSize or less
    If uFileSize = 0 Then
        ReDim aBlock(0)
        oCSP.TransformFinalBlock aBlock, 0, 0
        bDone = True
    Else
        With oRnd
            .OpenFile sFile
            Do
                If uBytesRead + uBlockSize < uFileSize Then
                    uBytesToRead = uBlockSize
                Else
                    uBytesToRead = uFileSize - uBytesRead
                    bDone = True
                End If
                ' Read in some bytes
                aBytes = .ReadBytes(uBytesToRead)
                aBlock = aBytes
                If bDone Then
                    oCSP.TransformFinalBlock aBlock, 0, uBytesToRead
                    uBytesRead = uBytesRead + uBytesToRead
                Else
                    uBytesRead = uBytesRead + oCSP.TransformBlock(aBlock, 0, uBytesToRead, aBlock, 0)
                End If
                DoEvents
            Loop Until bDone
            .CloseFile
        End With
    End If
    If bDone Then
        ' convert Hash byte array to an hexadecimal string
        aHash = oCSP.hash
        For i = 0 To UBound(aHash)
            Mid$(sHash, i * 2 + (aHash(i) > 15) + 2) = Hex(aHash(i))
        Next
    End If
    Application.ScreenUpdating = True
    ' Clean up
    oCSP.Clear
CleanUp:
    Set oFSO = Nothing
    Set oRnd = Nothing
    Set oCSP = Nothing
    GetFileHash = sHash
End Function

The output is pretty interesting, my test files indicates that BLOCKSIZE = 131071 (2^17-1) gives overall best performance with 32bit Office 2010 on Windows 7 x64, next best is 2^16-1 (65535). Note 2^27-1 yields Out of memory.

File Size (bytes) File Name
146,800,640 clonezilla-live-2.2.2-37-amd64.iso
798,210,048 HPIP201.2014_0902.29.iso
2,073,016,320 SW_DVD5_Windows_Vista_Business_W32_32BIT_English.ISO
4,380,387,328 Win10_1607_English_x64.iso
5,400,115,200 SW_DVD9_Windows_Svr_Std_and_DataCtr_2012_R2_64Bit_English.ISO

# Calculating all Files Hash from a root Folder

Another variation from the code above gives you more performance when you want to get hash codes of all files from a root folder including all sub folders.

# Example of Worksheet:

SampleWorksheet

# Code

Option Explicit

Private Const HashTypeMD5 As String = "MD5" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.md5cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA1 As String = "SHA1" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha1cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA256 As String = "SHA256" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha256cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA384 As String = "SHA384" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha384cryptoserviceprovider(v=vs.110).aspx
Private Const HashTypeSHA512 As String = "SHA512" ' https://msdn.microsoft.com/en-us/library/system.security.cryptography.sha512cryptoserviceprovider(v=vs.110).aspx

Private Const BLOCKSIZE As Double = 131071 ' 2^17-1

Private oFSO As Object
Private oCSP As Object
Private oRnd As Random ' Requires the Class from Microsoft https://support.microsoft.com/en-us/kb/189981
Private sHashType As String
Private sRootFDR As String
Private oRng As Range
Private uFileCount As Double

Sub AllFileHashes() ' Active-X button calls this
    Dim oWS As Worksheet
    ' | A: FileHash | B: FileSize | C: FileName | D: FilaName and Path | E: File Last Modification Time | F: Time required to calculate has code (seconds)
    With ThisWorkbook
        ' Clear All old entries on all worksheets
        For Each oWS In .Worksheets
            Set oRng = Intersect(oWS.UsedRange, oWS.UsedRange.Offset(2))
            If Not oRng Is Nothing Then oRng.ClearContents
        Next
        With .Worksheets(1)
            sHashType = Trim(.Range("A1").Value) ' Range(A1)
            sRootFDR = Trim(.Range("C1").Value) ' Range(C1) Column B for file size
            If Len(sHashType) = 0 Or Len(sRootFDR) = 0 Then Exit Sub
            Set oRng = .Range("A3") ' First entry on First Page
        End With
    End With
    
    uFileCount = 0
    If oRnd Is Nothing Then Set oRnd = New Random ' Class by Microsoft: Random
    If oFSO Is Nothing Then Set oFSO = CreateObject("Scripting.FileSystemObject") ' Just to get correct FileSize
    If oCSP Is Nothing Then Set oCSP = CreateObject("System.Security.Cryptography." & sHashType & "CryptoServiceProvider")
    
    ProcessFolder oFSO.GetFolder(sRootFDR)
    
    Application.StatusBar = False
    Application.ScreenUpdating = True
    oCSP.Clear
    Set oCSP = Nothing
    Set oRng = Nothing
    Set oFSO = Nothing
    Set oRnd = Nothing
    Debug.Print "Total file count: " & uFileCount
End Sub

Private Sub ProcessFolder(ByRef oFDR As Object)
    Dim oFile As Object, oSubFDR As Object, sHash As String, dStart As Date, dFinish As Date
    Application.ScreenUpdating = False
    For Each oFile In oFDR.Files
        uFileCount = uFileCount + 1
        Application.StatusBar = uFileCount & ": " & Right(oFile.Path, 255 - Len(uFileCount) - 2)
        oCSP.Initialize ' Reinitialize the CryptoServiceProvider
        dStart = Now
        sHash = GetFileHash(oFile, BLOCKSIZE, sHashType)
        dFinish = Now
        With oRng
            .Value = sHash
            .Offset(0, 1).Value = oFile.Size ' File Size in bytes
            .Offset(0, 2).Value = oFile.Name ' File name with extension
            .Offset(0, 3).Value = oFile.Path ' Full File name and Path
            .Offset(0, 4).Value = FileDateTime(oFile.Path) ' Last modification timestamp of file
            .Offset(0, 5).Value = dFinish - dStart ' Time required to calculate hash code
        End With
        If oRng.Row = Rows.Count Then
            ' Max rows reached, start on Next sheet
            If oRng.Worksheet.Index + 1 > ThisWorkbook.Worksheets.Count Then
                MsgBox "All rows in all worksheets have been used, please create more sheets"
                End
            End If
            Set oRng = ThisWorkbook.Sheets(oRng.Worksheet.Index + 1).Range("A3")
            oRng.Worksheet.Activate
        Else
            ' Move to next row otherwise
            Set oRng = oRng.Offset(1)
        End If
    Next
    'Application.StatusBar = False
    Application.ScreenUpdating = True
    oRng.Activate
    For Each oSubFDR In oFDR.SubFolders
        ProcessFolder oSubFDR
    Next
End Sub
    
Private Function GetFileHash(ByVal sFile As String, ByVal uBlockSize As Double, ByVal sHashType As String) As String
    Dim uBytesRead As Double, uBytesToRead As Double, bDone As Boolean
    Dim aBlock() As Byte, aBytes As Variant ' Arrays to store bytes
    Dim aHash() As Byte, sHash As String, i As Long, oTmp As Variant
    Dim uFileSize As Double ' Un-Comment if GetFileHash() is to be used individually
    
    If oRnd Is Nothing Then Set oRnd = New Random ' Class by Microsoft: Random
    If oFSO Is Nothing Then Set oFSO = CreateObject("Scripting.FileSystemObject") ' Just to get correct FileSize
    If oCSP Is Nothing Then Set oCSP = CreateObject("System.Security.Cryptography." & sHashType & "CryptoServiceProvider")
    
    If oFSO Is Nothing Or oRnd Is Nothing Or oCSP Is Nothing Then
        MsgBox "One or more required objects cannot be created"
        Exit Function
    End If
    
    uFileSize = oFSO.GetFile(sFile).Size ' FILELEN() has 2GB max
    uBytesRead = 0
    bDone = False
    sHash = String(oCSP.HashSize / 4, "0") ' Each hexadecimal is 4 bits
    
    ' Process the file in chunks of uBlockSize or less
    If uFileSize = 0 Then
        ReDim aBlock(0)
        oCSP.TransformFinalBlock aBlock, 0, 0
        bDone = True
    Else
        With oRnd
            On Error GoTo CannotOpenFile
            .OpenFile sFile
            Do
                If uBytesRead + uBlockSize < uFileSize Then
                    uBytesToRead = uBlockSize
                Else
                    uBytesToRead = uFileSize - uBytesRead
                    bDone = True
                End If
                ' Read in some bytes
                aBytes = .ReadBytes(uBytesToRead)
                aBlock = aBytes
                If bDone Then
                    oCSP.TransformFinalBlock aBlock, 0, uBytesToRead
                    uBytesRead = uBytesRead + uBytesToRead
                Else
                    uBytesRead = uBytesRead + oCSP.TransformBlock(aBlock, 0, uBytesToRead, aBlock, 0)
                End If
                DoEvents
            Loop Until bDone
            .CloseFile
CannotOpenFile:
            If Err.Number <> 0 Then ' Change the hash code to the Error description
                oTmp = Split(Err.Description, vbCrLf)
                sHash = oTmp(1) & ":" & oTmp(2)
            End If
        End With
    End If
    If bDone Then
        ' convert Hash byte array to an hexadecimal string
        aHash = oCSP.hash
        For i = 0 To UBound(aHash)
            Mid$(sHash, i * 2 + (aHash(i) > 15) + 2) = Hex(aHash(i))
        Next
    End If
    GetFileHash = sHash
End Function

# Remarks

# METHODS FOR THE CLASS BY MICROSOFT

Method Name Description
IsOpen Returns a boolean to indicate whether the file is open.
OpenFile(sFileName As String) Opens the file specified by the sFileName argument.
CloseFile Closes the currently open file.
ReadBytes(ByteCount As Long) Reads ByteCount bytes and returns them in a Variant byte array and moves the pointer.
WriteBytes(DataBytes() As Byte) Writes the contents of the byte array to the current position in the file and moves the pointer.
Flush Forces Windows to flush the write cache.
SeekAbsolute(HighPos As Long, LowPos As Long) Moves the file pointer to the designated position from the beginning of the file. Though VBA treats the DWORDS as signed values, the API treats them as unsigned. Make the high-order argument non-zero to exceed 4GB. The low-order DWORD will be negative for values between 2GB and 4GB.
SeekRelative(Offset As Long) Moves the file pointer up to +/- 2GB from the current location. You can rewrite this method to allow for offsets greater than 2GB by converting a 64-bit signed offset into two 32-bit values.

# PROPERTIES OF THE CLASS BY MICROSOFT

Property Description
FileHandle The file handle for the currently open file. This is not compatible with VBA file handles.
FileName The name of the currently open file.
AutoFlush Sets/indicates whether WriteBytes will automatically call the Flush method.

# NORMAL MODULE

Function Notes
GetFileHash(sFile As String, uBlockSize As Double, sHashType As String) Simply throw in the full path to be hashed, Blocksize to use (number of bytes), and the type of Hash to use - one of the private constants: HashTypeMD5, HashTypeSHA1, HashTypeSHA256, HashTypeSHA384, HashTypeSHA512. This was designed to be as generic as possible.

You should un/comment the uFileSize As Double accordingly. I have tested MD5 and SHA1.