[RESOLVED] byval confusion

[shantanu@india]

Hi all,
I am learning to use API's but feel a bit confused with the way "ByVal" is used in the function Declare statement.By definition of a function if "ByVal" is used then the original argument is not affected.Here's my examle:

Option Explicit

Private Declare Function GetWindowsDirectory Lib "kernel32" Alias "GetWindowsDirectoryA" (ByVal lpBuffer As String, ByVal nSize As Long) As Long


Private Sub Command1_Click()
Dim retstr  As String * 255
Dim retval  As Long

retstr = "hello world"
retval = GetWindowsDirectory(retstr, 255)

Label1.Caption = retstr
End Sub

This obviously generates the output "C"\WINDOWS" as expected.

My question is why should the string variable 'retstr' contain anything other than "hello world" since the argument is being passed as "ByVal"?

[DigiRev]

When passing a string by value to an API function, VB automatically passes the pointer to that string as if it were passed by reference.

[shantanu@india]

Thanks ...that clears my confusion.