Upgrade Recommendation: Adjust Data Types for Win32 APIs
Many APIs can be used exactly as they were in Visual Basic 6.0, with the caveat that you have to adjust your data types accordingly. The Visual Basic 6.0 Long data type is now the Visual Basic 2008 Integer data type, and the Visual Basic 6.0 Integer data type is now the Visual Basic 2008 Short data type. During the upgrade, these changes are made for you, and simple APIs work exactly the same as they did in Visual Basic 6.0. For example:
Private Declare Function GetVersion Lib "kernel32" () As Long
Function GetVer()
Dim Ver As Long
Ver = GetVersion()
MsgBox ("System Version is " & Ver)
End Function
changes to:
Private Declare Function GetVersion Lib "kernel32" () As Integer
Function GetVer()
Dim Ver As Integer
Ver = GetVersion()
MsgBox("System Version is " & Ver)
End Function
In addition to numeric data type upgrades, Visual Basic 6.0 has a fixed-length string data type which is not supported in Visual Basic 2008, and which is upgraded to a fixed-length string wrapper class. In many cases in Visual Basic 6.0 you can perform the same action using a normal string. For example:
Private Declare Function GetUserName Lib "advapi32.dll" Alias _
"GetUserNameA" (ByVal lpBuffer As String, ByRef nSize As Long) As Long
Function GetUser()
Dim Ret As Long
Dim UserName As String
Dim Buffer As String * 25
Ret = GetUserName(Buffer, 25)
UserName = Left$(Buffer, InStr(Buffer, Chr(0)) - 1)
MsgBox (UserName)
End Function
can be better written using a normal string explicitly set to length 25 instead of a fixed-length string:
Dim Buffer As String
Buffer = String$(25, " ")
This is upgraded to Visual Basic 2008 as follows:
Declare Function GetUserName Lib "advapi32.dll" Alias _
"GetUserNameA" (ByVal lpBuffer As String, ByRef nSize As Integer) As Integer
Function GetUser()
Dim Ret As Integer
Dim UserName As String
Dim Buffer As String
Buffer = New String(CChar(" "), 25)
Ret = GetUserName(Buffer, 25)
UserName = Left(Buffer, InStr(Buffer, Chr(0)) - 1)
MsgBox(UserName)
End Function
In some cases, Visual Basic 2008 better handles passing strings to APIs, since you can optionally declare how you want strings to be passed using the ANSI and UNICODE keywords.
There are three cases where you may need to make some changes. The first is passing user-defined types that contain fixed-length strings or byte arrays to APIs. In Visual Basic 2008 you may need to change your code, adding the MarshallAs attribute (from the System.Runtime.InteropServices namespace) to each fixed-length string or byte array in the user-defined type. The second case is using the As Any variable type in a Declare statement. This is not supported in Visual Basic 2008. Variables of type As Any were often used to pass a variable that was either a string or Null; you can replace this Visual Basic 6.0 usage by declaring two forms of the API, one with longs, one with strings. For example, the GetPrivateProfileString API has a parameter lpKeyName of type As Any:
Private Declare Function GetPrivateProfileString Lib "kernel32" Alias _
"GetPrivateProfileStringA" (ByVal lpApplicationName As String, ByVal _
lpKeyName As Any, ByVal lpDefault As String, ByVal lpReturnedString _
As String, ByVal nSize As Long, ByVal lpFileName As String) As Long
You can remove the "As Any" by replacing the Declare with two versions, one that accepts a long, and one that accepts a string:
Private Declare Function GetPrivateProfileStringKey Lib "kernel32" Alias _
"GetPrivateProfileStringA" (ByVal lpApplicationName As String, ByVal _
lpKeyName As String, ByVal lpDefault As String, ByVal lpReturnedString _
As String, ByVal nSize As Integer, ByVal lpFileName As String) As Integer
Private Declare Function GetPrivateProfileStringNullKey Lib "kernel32" _
Alias "GetPrivateProfileStringA" (ByVal lpApplicationName As String, _
ByVal lpKeyName As Integer, ByVal lpDefault As String, ByVal _
lpReturnedString As String, ByVal nSize As Long, ByVal lpFileName _
As String) As Integer
When you wish to pass the value Null to the API, you use the GetPrivateProfileStringNullKey version. Doing it this way means that the function upgrades to Visual Basic 2008.
The final area where you may need to make some changes is if you are using APIs that perform thread creation, derive from Windows classes, perform message queue hooking, and so on. Some of these functions will cause a run-time error in Visual Basic 2008. Many of these APIs have equivalents in Visual Basic 2008 or the .NET Framework. You will have to fix these on a case-by-case basis.