How to make WinHttpCrackUrl work in 64-bit - windows

Question

I have Visual Basic for Applications code that uses WinHttp and works flawlessly with 32-bit Office 2010 running on 32-bit Windows XP. The same code fails to run properly on 64-bit Office 2013 on 64-bit Windows 8, even though it compiles fine.
The problem is that WinHttpCrackUrl() returns an error 87 "The parameter is incorrect" on Windows 8.
I have double-checked and triple-checked that all pointers are declared as LongPtr in the code where appropriate. What am I doing wrong?
Here is the code that runs fine on 32-bit Excel/Windows, but fails to run on 64-bit Excel/Windows:
Private Type URL_COMPONENTS
dwStructSize As Long
lpszScheme As LongPtr
dwSchemeLength As Long
nScheme As Long
lpszHostName As LongPtr
dwHostNameLength As Long
nPort As Long
lpszUserName As LongPtr
dwUserNameLength As Long
lpszPassword As LongPtr
dwPasswordLength As Long
lpszUrlPath As LongPtr
dwUrlPathLength As Long
lpszExtraInfo As LongPtr
dwExtraInfoLength As Long
End Type
Private Declare PtrSafe Function WinHttpCrackUrl Lib "WinHTTP" ( _
ByVal pwszUrl As LongPtr, _
ByVal dwUrlLength As Long, _
ByVal dwFlags As Long, _
ByRef lpUrlComponents As URL_COMPONENTS) As Long
Sub Test()
Dim result as Long
Dim URLComp As URL_COMPONENTS
Dim mURL as String
mURL = "http://www.stackoverflow.com" & vbNullChar
With URLComp
.dwStructSize = Len(URLComp)
.dwHostNameLength = -1
.dwSchemeLength = -1
.dwUrlPathLength = -1
End With
result = WinHttpCrackUrl(StrPtr(mURL), 0, 0, URLComp)
' Prints 1 on 32-bit Excel/Windows (indicating success)
' Prints 0 on 64-bit Excel/Windows (indicating failure)
Debug.Print result
' Prints 87 on 64-bit Excel/Windows ("The parameter is incorrect.")
Debug.Print err.LastDllError
End Sub

Answer 1

The struct is aligned in the C++ code, but VBA structs are packed. In 32 bit, for your struct, it does not matter since all members have alignment 4. But in 64 bit the pointers need 8 byte alignment and the struct has some extra padding. Put it in like this:
Private Type URL_COMPONENTS
dwStructSize As Long
padding1 As Long
lpszScheme As LongPtr
dwSchemeLength As Long
nScheme As Long
lpszHostName As LongPtr
dwHostNameLength As Long
nPort As Long
lpszUserName As LongPtr
dwUserNameLength As Long
padding2 As Long
lpszPassword As LongPtr
dwPasswordLength As Long
padding3 As Long
lpszUrlPath As LongPtr
dwUrlPathLength As Long
padding4 As Long
lpszExtraInfo As LongPtr
dwExtraInfoLength As Long
padding5 As Long
End Type
I guess you'll want some conditional compilation to switch better 32 and 64 bit versions but I must confess to having no idea how to do that with VBA.