How to generate md5-hashes for large files with VBA?

Question

I have the following functions to generate md5-hashes for files. The functions work great for small files, but crashes and generate Run-time error 7 - Out of memory<

Answer 1

It looks like you reached the memory limit. A better way would be to compute the MD5 of the file by block:

Public Function ComputeMD5(filepath As String) As String
  Dim buffer() As Byte, svc As Object, hFile%, blockSize&, i&
  blockSize = 2 ^ 16

  ' open the file '

  If Len(Dir(filepath)) Then Else Err.Raise 5, , "file not found" & vbCr & filepath

  hFile = FreeFile
  Open filepath For Binary Access Read As hFile

  ' allocate buffer '

  If LOF(hFile) < blockSize Then blockSize = ((LOF(hFile) + 1024) \ 1024) * 1024
  ReDim buffer(0 To blockSize - 1)

  ' compute hash '

  Set svc = CreateObject("System.Security.Cryptography.MD5CryptoServiceProvider")

  For i = 1 To LOF(hFile) \ blockSize
    Get hFile, , buffer
    svc.TransformBlock buffer, 0, blockSize, buffer, 0
  Next

  Get hFile, , buffer
  svc.TransformFinalBlock buffer, 0, LOF(hFile) Mod blockSize
  buffer = svc.Hash

  ' cleanup '

  svc.Clear
  Close hFile

  ' convert to an hexa string '

  ComputeMD5 = String$(32, "0")

  For i = 0 To 15
     Mid$(ComputeMD5, i + i + 2 + (buffer(i) > 15)) = Hex(buffer(i))
  Next

End Function