Testing for a string of zero bytes

[simonc]

I am reading a series of bytes (around 2000) from a binary file and want the
quickest way to test if all the bytes have a value zero. Would this be by a
string comparison? I'm sure reading the bytes into a byte array and testing
each one individually is NOT the best way. Incidentally I have to repeat this
operation several hundred thousand times so any gain in speed will be
significant.

Grateful for advice.

 

[Mike H]

Hi,

If InStr(mystring, "1") Then
MsgBox "contains ones"
Else
MsgBox "all zeroes"
End If

Mike

 

[Peter T]

You mean you are looking for a string that consists purely of vbNullChar's ?

I'm sure reading the bytes into a byte array and testing
each one individually is NOT the best way

Think I'd do exactly that, looping a byte array is one of the fastest things
you can do in VBA
This does 2000 * 30 * 2 = 120k loops in a blink

Sub test()
Dim bNotAllZero As Boolean
Dim i As Long, j As Long
Dim s As String
Dim ba() As Byte

s = String(30, vbNullChar)
s = s & "a" ' uncomment for testing

ba = s

For j = 1 To 2000
For i = 0 To UBound(ba)
If ba(i) > 0 Then
bNotAllZero = True
Exit For
End If
Next
Next
MsgBox bNotAllZero & vbCr & _
(j - 1) * (i) & " loops"

End Sub

Regards,
Peter T

 

[Peter T]

Maybe a simple string comparison is faster. But it depends what you want to
do overall (eg other checking of the bytes), chances of a non-nullchar near
the beginning, etc. Try both methods with your actual data

Sub test2()
Dim bNotAllZero As Boolean
Dim i As Long, j As Long
Dim s As String, s2 As String
Dim ba() As Byte

s = String(2000, vbNullChar)
s2 = String(Len(s), vbnullcar)

's = s & "a" ' uncomment for testing

For i = 1 To 2000
bNotAllZero = s <> s2
Next

MsgBox bNotAllZero
End Sub

Note I increased the length to 2000 as you say that's what you are dealing
with.

Regards,
Peter T

 

[RB Smissaert]

It all depends a bit how you have these bytes.
Are they in a string variable, in an array or are they still in a file?
Post the relevant code.

RBS