Check result of call into Windows API

28 Jul 2006 3:44 PM

Lee

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 Silver
// Information Concepts Inc.
//
// Converting data into information since 1981

31 Jul 2006 6:47 PM

Greg Young

Try user32 instead of user32.dll in your dllimport (it should work like a
charm).

>   <DllImport("user32", _
>              EntryPoint:="MessageBeep", _
>              SetLastError:=True, _
>              CallingConvention:=CallingConvention.StdCall)> _
>   Public Function MessageBeep(ByVal wType As Int32) As Boolean
>   End Function

Also you might want to take a look at this
http://www.codeproject.com/vb/net/apiexception.asp as it seems to be
discussing exactly what you are trying to do.

Cheers,

Greg Young
MVP - C#
http://codebetter.com/blogs/gregyoung

Show quote

"Lee" <lsil***@information-concepts.com> wrote in message
news:1154101496.739529.253460@m79g2000cwm.googlegroups.com...
> 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 Silver
> // Information Concepts Inc.
> //
> // Converting data into information since 1981
>

31 Jul 2006 9:00 PM

Lee

Greg:

Thanks for the response.

I found the answer(s) I needed in the .VB newsgroup...

It looks like MessageBeep will always succeed -- or at least not fail
for an invalid parameter.

I modified my test to use GetTempFileName specifying an invalid path
and the error detection worked just as it should.

--
// Lee Silver
// Information Concepts Inc.
//
// Converting Data into Information since 1981

Greg Young wrote:

Show quote

> Try user32 instead of user32.dll in your dllimport (it should work like a
> charm).
>
> >   <DllImport("user32", _
> >              EntryPoint:="MessageBeep", _
> >              SetLastError:=True, _
> >              CallingConvention:=CallingConvention.StdCall)> _
> >   Public Function MessageBeep(ByVal wType As Int32) As Boolean
> >   End Function
>
> Also you might want to take a look at this
> http://www.codeproject.com/vb/net/apiexception.asp as it seems to be
> discussing exactly what you are trying to do.
>
> Cheers,
>
> Greg Young
> MVP - C#
> http://codebetter.com/blogs/gregyoung
>