How To Convert Between Signed and Unsigned Numbers

Summary

Visual Basic for Applications only supports signed 2- and 4-byte Integers, while other languages, such as C, support both signed and unsigned Integers. This article provides conversion functions between signed and unsigned 4-byte Integers and between signed and unsigned 2-byte Integers.

More Information

In VBA, the range of Integer values is from -32768 to +32767, and for Long values from -2147483648 to 2147483647. When making API calls or calling a DLL written in C, you may be requested to pass in or receive unsigned values in the range of 0 to 65535 or 0 to 4294967296. The conversion functions provided below convert an unsigned Integer to a Long and also from an unsigned Long to a Double for purposes of input and display or other calculations.


The four functions are:
UnsignedToLong
LongToUnsigned
UnsignedToInteger
IntegerToUnsigned

UnsignedToLong


The function takes a Double containing a value in the range of an unsigned Long and returns a Long that you can pass to an API that requires an unsigned Long.

LongToUnsigned


The function takes an unsigned Long from an API and converts it to a Double for display or arithmetic purposes.

UnsignedToInteger


The function takes a Long containing a value in the range of an unsigned Integer and returns an Integer that you can pass to an API that requires an unsigned Integer.

IntegerToUnsigned


The function takes an unsigned Integer from and API and converts it to a Long for display or arithmetic purposes.


   Declare Function MyAPI Lib "xxx" (Value As Long) As Long
Dim uResult As Long
uResult = MyAPI(UnsignedToLong(3300000000))
Debug.Print "Return Code: " & LongToUnsigned(uResult)

In the above example, the MyAPI API accepts an unsigned Long as a parameter and returns an unsigned Long as a result code. Because VBA only understands signed Longs, the DECLARE statement uses signed Longs. The UnsignedToLong
function converts a number outside the range of signed Long (but within the
range of an unsigned Long) into a signed Long for purposes of calling the API. The LongToUnsigned function performs the opposite conversion.


Without these functions, the input argument would have to have been specified as a signed Long, in this case -994967296, and the return value would have to be displayed as a signed value, possibly also as a negative number and non-intuitive.

Step by Step Example

  1. Create a new VBA project.
  2. Add the following code to a Module:
          Option Explicit

    Private Const OFFSET_4 = 4294967296#
    Private Const MAXINT_4 = 2147483647
    Private Const OFFSET_2 = 65536
    Private Const MAXINT_2 = 32767

    Function UnsignedToLong(Value As Double) As Long
    If Value < 0 Or Value >= OFFSET_4 Then Error 6 ' Overflow
    If Value <= MAXINT_4 Then
    UnsignedToLong = Value
    Else
    UnsignedToLong = Value - OFFSET_4
    End If
    End Function

    Function LongToUnsigned(Value As Long) As Double
    If Value < 0 Then
    LongToUnsigned = Value + OFFSET_4
    Else
    LongToUnsigned = Value
    End If
    End Function

    Function UnsignedToInteger(Value As Long) As Integer
    If Value < 0 Or Value >= OFFSET_2 Then Error 6 ' Overflow
    If Value <= MAXINT_2 Then
    UnsignedToInteger = Value
    Else
    UnsignedToInteger = Value - OFFSET_2
    End If
    End Function

    Function IntegerToUnsigned(Value As Integer) As Long
    If Value < 0 Then
    IntegerToUnsigned = Value + OFFSET_2
    Else
    IntegerToUnsigned = Value
    End If
    End Function
  3. Visual Basic only: Run the project and pause it.
  4. Type the following in the Immediate/Debug Window:
          ?UnsignedToLong(3300000000)
    ?LongToUnsigned(-55)
    ?UnsignedToInteger(45000)
    ?IntegerToUnsigned(-3000)
  5. You will get the following results:
    -994967296
    4294967241
    -20536
    62536

References

For additional information, please see the following article in the Microsoft Knowledge Base:
112673 How To Pass & Return Unsigned Integers to DLLs from VB
Propiedades

Id. de artículo: 189323 - Última revisión: 03/23/2009 - Revisión: 1

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