Convert Byte Array to Corresponding Numeric Value

Category:

Dates and Math

Type:

Snippets

Difficulty:

Advanced

Author:

Imran Zaheer

Version Compatibility:

More information:

This function transforms a byte array to a numeric value in the same manner an application would transform bytes in memory to values. See comments for explanation and example.

Instructions: Copy the declarations and code below and paste directly into your VB project.

Declarations:
' (None)

Code:

Function BytesToNumEx(ByteArray() As Byte, StartRec As Long, _
   EndRec As Long, UnSigned As Boolean) As Double
' ###################################################
' Author                : Imran Zaheer
' Contact               : imraanz@mail.com
' Date                  : January 2000
' Function BytesToNumEx : Convertes the specified byte array
'                         into the corresponding Integer or Long
'                         or any signed/unsigned
'                        ;(non-float) data type.
'
' * BYTES : LIKE NUMBERS(Integer/Long etc.) STORED IN A
' * BINARY FILE

' Parameters :
'  (All parameters are reuuired: No Optional)
'     ByteArray() : byte array containg a number in byte format
'  StartRec    : specify the starting array record within the
                 ' array
'     EndRec      : specify the end array record within the array
'     UnSigned    : when False process bytes for both -ve and
'                   +ve values.
'                   when true only process the bytes for +ve
'                   values.
'
' Note: If both "StartRec" and "EndRec" Parameters are zero,
'       then the complete array will be processed.
'
' Example Calls :
'      dim myArray(1 To 4) as byte
'      dim myVar1 as Integer
'      dim myVar2 as Long
'
'      myArray(1) = 255
'      myArray(2) = 127
'      myVar1 = BytesToNumEx(myArray(), 1, 2, False)
'  after execution of above statement myVar1 will be 32767
'
'      myArray(1) = 0
'      myArray(2) = 0
'      myArray(3) = 0
'      myArray(4) = 128
'      myVar2 = BytesToNumEx(myArray(), 1, 4, False)
'  after execution of above statement myVar2 will be -2147483648
'
'
'####################################################
On Error GoTo ErrorHandler
Dim i As Integer
Dim lng256 As Double
Dim lngReturn As Double
    
    lng256 = 1
    lngReturn = 0
    
    If EndRec < 1 Then
        EndRec = UBound(ByteArray)
    End If
    
    If StartRec > EndRec Or StartRec < 0 Then
        MsgBox _
         "Start record can not be greater then End record...!", _
          vbInformation
        BytesToNumEx = -1
        Exit Function
    End If
    
    lngReturn = lngReturn + (ByteArray(StartRec))
    For i = (StartRec + 1) To EndRec
        lng256 = lng256 * 256
        If i < EndRec Then
            lngReturn = lngReturn + (ByteArray(i) * lng256)
        Else
           ' if -ve

If ByteArray(i) > 127 And UnSigned = False Then
             lngReturn = (lngReturn + ((ByteArray(i) - 256) _
                  * lng256))
            Else
                lngReturn = lngReturn + (ByteArray(i) * lng256)
            End If
        End If
    Next i
    
    BytesToNumEx = lngReturn
ErrorHandler:
End Function