> (I also posted this query in Microsoft.Public.DotNet.Framework
> yesterday, but since I have received no responses, I am posting it here
> too.)
>
> Using Windows XP with all updates applied and Visual Studio 2.0.
>
> I am trying to develop some common error-handling of Windows API
> invocations that fail and am using MessageBeep as the API to test with.
>
> Given 1) the following Imports statement:
>
>    Imports System.Runtime.InteropServices
>
> 2) the following declaration of MessageBeep:
>
>    <DllImport("user32.dll", _
>               EntryPoint:="MessageBeep", _
>               SetLastError:=True, _
>               CallingConvention:=CallingConvention.StdCall)> _
>    Public Function MessageBeep(ByVal wType As Int32) As Boolean
>    End Function
>
> 3) the following code to test passing an invalid value to MessageBeep
>
>          Dim MBResult As Boolean
>          Dim MBErrorCode As Integer
>
>          MBResult = MessageBeep(-2)
>
>          If MBResult Then
>             MBErrorCode = Marshal.GetLastWin32Error
>          End If
>
> When I set a break-point after the assignment to MBErrorCode, I see
> that it has a value of 127 -- "The specified procedure could not be
> found". I was expecting a value of 87 -- "The parameter is incorrect".
>
> Note that when I pass MessageBeep a value of 0 -- a presumably valid
> value -- I get the same result.

> Lee wrote:
> > (I also posted this query in Microsoft.Public.DotNet.Framework
> > yesterday, but since I have received no responses, I am posting it here
> > too.)
> >
> > Using Windows XP with all updates applied and Visual Studio 2.0.
> >
> > I am trying to develop some common error-handling of Windows API
> > invocations that fail and am using MessageBeep as the API to test with.
> >
> > Given 1) the following Imports statement:
> >
> >    Imports System.Runtime.InteropServices
> >
> > 2) the following declaration of MessageBeep:
> >
> >    <DllImport("user32.dll", _
> >               EntryPoint:="MessageBeep", _
> >               SetLastError:=True, _
> >               CallingConvention:=CallingConvention.StdCall)> _
> >    Public Function MessageBeep(ByVal wType As Int32) As Boolean
> >    End Function
> >
> > 3) the following code to test passing an invalid value to MessageBeep
> >
> >          Dim MBResult As Boolean
> >          Dim MBErrorCode As Integer
> >
> >          MBResult = MessageBeep(-2)
> >
> >          If MBResult Then
> >             MBErrorCode = Marshal.GetLastWin32Error
> >          End If
> >
> > When I set a break-point after the assignment to MBErrorCode, I see
> > that it has a value of 127 -- "The specified procedure could not be
> > found". I was expecting a value of 87 -- "The parameter is incorrect".
> >
> > Note that when I pass MessageBeep a value of 0 -- a presumably valid
> > value -- I get the same result.
>
> Lee - MessageBeep is probably not a good choice for this.  From the
> remarks section of the MSDN help:
>
> [quote]
> If it cannot play the specified alert sound, MessageBeep attempts to
> play the system default sound.
> [/quote]
>
> What that means is that this function won't really fail for an invalid
> value - it will simply play the system default sound.  And that is what
> it does on my system, it plays the sound even with an invalid value and
> the function returns true.
>
> --
> Tom Shelton [MVP]

> Tom:
>
> Thanks for the feed-back.
>
> I guess I mis-interpreted the docs and thought that an invalid value
> would cause MessageBeep to fail.
>
> I'll try a different API function and post my results here.
>
> --
> // Lee Silver
> // Information Concepts Inc.
> //
> // Converting Data into Information since 1981
>
>
> Tom Shelton wrote:
> > Lee wrote:
> > > (I also posted this query in Microsoft.Public.DotNet.Framework
> > > yesterday, but since I have received no responses, I am posting it here
> > > too.)
> > >
> > > Using Windows XP with all updates applied and Visual Studio 2.0.
> > >
> > > I am trying to develop some common error-handling of Windows API
> > > invocations that fail and am using MessageBeep as the API to test with.
> > >
> > > Given 1) the following Imports statement:
> > >
> > >    Imports System.Runtime.InteropServices
> > >
> > > 2) the following declaration of MessageBeep:
> > >
> > >    <DllImport("user32.dll", _
> > >               EntryPoint:="MessageBeep", _
> > >               SetLastError:=True, _
> > >               CallingConvention:=CallingConvention.StdCall)> _
> > >    Public Function MessageBeep(ByVal wType As Int32) As Boolean
> > >    End Function
> > >
> > > 3) the following code to test passing an invalid value to MessageBeep
> > >
> > >          Dim MBResult As Boolean
> > >          Dim MBErrorCode As Integer
> > >
> > >          MBResult = MessageBeep(-2)
> > >
> > >          If MBResult Then
> > >             MBErrorCode = Marshal.GetLastWin32Error
> > >          End If
> > >
> > > When I set a break-point after the assignment to MBErrorCode, I see
> > > that it has a value of 127 -- "The specified procedure could not be
> > > found". I was expecting a value of 87 -- "The parameter is incorrect".
> > >
> > > Note that when I pass MessageBeep a value of 0 -- a presumably valid
> > > value -- I get the same result.
> >
> > Lee - MessageBeep is probably not a good choice for this.  From the
> > remarks section of the MSDN help:
> >
> > [quote]
> > If it cannot play the specified alert sound, MessageBeep attempts to
> > play the system default sound.
> > [/quote]
> >
> > What that means is that this function won't really fail for an invalid
> > value - it will simply play the system default sound.  And that is what
> > it does on my system, it plays the sound even with an invalid value and
> > the function returns true.
> >
> > --
> > Tom Shelton [MVP]

> Per Tom's suggestion I changed my test to use the GetTempFileName and
> got the same result. My changes were as follows:
>
> 1)
>
>    <DllImport("kernel32.dll", _
>               EntryPoint:="GetTempFileNameA", _
>               CharSet:=CharSet.Ansi, _
>               ExactSpelling:=True, _
>               CallingConvention:=CallingConvention.StdCall)> _
>    Public Function GetTempFileName(ByVal Path As String, _
>                                    ByVal PrefixString As String, _
>                                    ByVal Unique As Integer, _
>                                    ByVal TempFileName As
> Text.StringBuilder) As Integer
>    End Function
>
> and 2)
>
>          Dim GTFName As New Text.StringBuilder(255)
>          Dim GTFResult As Integer
>          Dim GTFErrorCode As Integer
>
>          GTFResult = GetTempFileName("x:\temp" & Chr(0), _
>                                      "zzzz" & Chr(0), _
>                                      0, _
>                                      GTFName)
>          If GTFResult = 0 Then
>             GTFErrorCode = Marshal.GetLastWin32Error
>          End If
>
>
> GTFResult is 0 (failure) after the call to GetTempFileName, and
> GTFErrorCode is 127. Note that I am forcing an error because "x:\temp"
> does not exist (I have no X drive), but the error-code seems to be
> wrong.
>

> Looking at this and your last example, I realize what the problem is...
>  You aren't adding the SetLastError:=True to your DllImport attribute.
> Without that, the api error code is not saved.
>
> Now for a couple of api suggestions...
>
> 1) You don't need to null terminate your strings (the Chr(0)), the
> marshaller will take care of that for you.  That was true in VB6 as
> well as .NET.  It won't hurt anything really, but it is just extra
> overhead that doesn't need to happen.
>
> 2) Don't hard code to the A/W versions of your calls.  The runtime
> marshaller can work that out for you as well.  In other words, your
> declare would look like:
>
>     <DllImport("kernel32", CharSet:=CharSet.Auto, SetLastError:=True)>
> _
>     Private Function GetTempFileName( _
>         ByVal lpPathName As String, _
>         ByVal lpPrefixString As String, _
>         ByVal uUnique As Integer, _
>         ByVal lpTempFileName As StringBuilder) As Integer
>
>     End Function
>
> The runtime will call the W function on systems were it is available,
> avoiding the extra string conversions required for the A function on NT
> boxes.
>
> 3)  Why don't you just use the VB declare syntax?
> Private Declare Auto Function GetTempFileName Lib "kernel" (.....) As
> Integer
> That will set all the necessary attribute fields (like SetLastError).
>
> Don't take any of the above as critizism, just friendly advice.  Anyway
> here is my code for your example:
>
> Option Explicit On
> Option Strict On
>
> Imports System
> Imports System.Text
> Imports System.ComponentModel
> Imports System.Runtime.InteropServices
>
> Module Module1
>
>     <DllImport("kernel32", CharSet:=CharSet.Auto, SetLastError:=True)>
> _
>     Private Function GetTempFileName( _
>         ByVal lpPathName As String, _
>         ByVal lpPrefixString As String, _
>         ByVal uUnique As Integer, _
>         ByVal lpTempFileName As StringBuilder) As Integer
>     End Function
>
>     'Private Declare Auto Function GetTempFileName Lib "kernel32" ( _
>     '    ByVal lpPathName As String, _
>     '    ByVal lpPrefixString As String, _
>     '    ByVal uUnique As Integer, _
>     '    ByVal lpTempFileName As StringBuilder) As Integer
>
>     Sub Main()
>         Dim tempFile As New StringBuilder(260)
>
>         If GetTempFileName("x:\temp", "zzzz", 0, tempFile) = 0 Then
>
>             Dim exception As New
> Win32Exception(Marshal.GetLastWin32Error())
>             Console.WriteLine( _
>                "The error code was {0} and the message was {1}", _
>                 exception.ErrorCode, exception.Message)
>
>         End If
>     End Sub
> End Module
>
> --
> Tom Shelton [MVP]