What is the fastest way to tell if one file is equal to another?

[VaxoP]

Anyone know?
Id assume the first check would be to just see if the filesizes are the same, and if they are.. then what? Should I do a CRC32 checksum? Or just load the data of the files into 2 strings and see if they are the same? What is the fastest way to do so?

[CVMichael]

If you load in a string, since a string is unicode, you take twice the memory of the file, and since you open 2 files, you take quite a lot of memory....

You should load in a byte array, like this:

Option Explicit

Private Sub Form_Load()
    Dim File1() As Byte
    Dim File2() As Byte
    Dim K As Long
    
    Open "C:\File1.txt" For Binary Access Read As #1
    Open "C:\File2.txt" For Binary Access Read As #2
        ReDim File1(LOF(1) - 1)
        ReDim File2(LOF(2) - 1)
        
        Get #1, , File1
        Get #2, , File2
    Close #1, #2
    
    For K = 0 To UBound(File1)
        If File1(K) <> File2(K) Then Exit For
    Next K
    
    If K = UBound(File1) + 1 Then
        MsgBox "Files contain the same data", vbInformation
    Else
        MsgBox "Files are not the same at position: " & K, vbInformation
    End If
End Sub

And if the files are very big, then it would be better to load chunks at a time instead of the whole file (if you don't know how to do that I can write a short example for you)

[Code Doc]

CVMichael aid, "And if the files are very big, then it would be better to load chunks at a time instead of the whole file (if you don't know how to do that I can write a short example for you)."
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I tried your code using a matched pair of 3.3 Mb Rtf files. I'm not sure what your definition of "very big" is, but the code ran with these two files in about a millisecond or so on my 1.7 GHz machine. I didn't use a timer control to check it, but my eyes don't blink much faster.