GetLastWin32Error questions

[active]

GetLastWin32Error exposes the Win32 GetLastError API method from
Kernel32.DLL. This method exists because it is not safe to make a direct
platform invoke call to GetLastError to obtain this information. If you want
to access this error code, you must call GetLastWin32Error rather than
writing your own platform invoke definition for GetLastError and calling it.
The common language runtime can make internal calls to APIs that overwrite
the operating system maintained GetLastError.

You can only use this method to obtain error codes if you apply the
System.Runtime.InteropServices.DllImportAttribute to the method signature
and set the SetLastError field to true. The process for this varies
depending upon the source language used: C# and C++ are false by default,
but the Declare statement in Visual Basic is true. For additional
information about the GetLastError and SetLastError Win32 API methods, see
the MSDN Library.

What does the last paragraph mean?

Especially the "...only...if you apply the ..." part

What Declare are they taking about?

I'd like to messagebox only if there is an error.

How can I test for success/failure?

Thanks a lot

[Michael Phillips, Jr.]

What does the last paragraph mean?

>
Especially the "...only...if you apply the ..." part

What Declare are they taking about?

System.Runtime.InteropServices.DllImportAttribute to the method signature
and set the SetLastError field to true.

Below is an example of what the last paragraph is talking about:

<DllImport("ole32.dll", EntryPoint:="CLSIDFromString", _
SetLastError:=True, CharSet:=CharSet.Auto, _
CallingConvention:=CallingConvention.StdCall)_
Public Shared Function CLSIDFromString( _
<MarshalAs(UnmanagedType.LPWStr)ByVal pwcsName As String, _
ByRef pclsid As Guid) As Integer
End Function

" active" <ac**********@a-znet.comwrote in message
news:O2*************@TK2MSFTNGP05.phx.gbl...

GetLastWin32Error exposes the Win32 GetLastError API method from
Kernel32.DLL. This method exists because it is not safe to make a direct
platform invoke call to GetLastError to obtain this information. If you
want to access this error code, you must call GetLastWin32Error rather
than writing your own platform invoke definition for GetLastError and
calling it. The common language runtime can make internal calls to APIs
that overwrite the operating system maintained GetLastError.

You can only use this method to obtain error codes if you apply the
System.Runtime.InteropServices.DllImportAttribute to the method signature
and set the SetLastError field to true. The process for this varies
depending upon the source language used: C# and C++ are false by default,
but the Declare statement in Visual Basic is true. For additional
information about the GetLastError and SetLastError Win32 API methods, see
the MSDN Library.

What does the last paragraph mean?

Especially the "...only...if you apply the ..." part

What Declare are they taking about?

I'd like to messagebox only if there is an error.

How can I test for success/failure?

Thanks a lot

[active]

I think I've got it.
Since I'm using Declares I need not do it.
But if I do a DllImport in C# I must do it if I want to use
GetLastWin32Error after calling that sub.
Right?

But what about sending to a messagebox only if there is an error.

How can I test for success/failure?

Is not zero always an error and zero return success?
As always, thanks for the help!


"Michael Phillips, Jr." <mp*********@nospam.jun0.c0mwrote in message
news:%2****************@TK2MSFTNGP05.phx.gbl...

>What does the last paragraph mean?

Especially the "...only...if you apply the ..." part

What Declare are they taking about?

>System.Runtime.InteropServices.DllImportAttribu te to the method signature
and set the SetLastError field to true.

Below is an example of what the last paragraph is talking about:

<DllImport("ole32.dll", EntryPoint:="CLSIDFromString", _
SetLastError:=True, CharSet:=CharSet.Auto, _
CallingConvention:=CallingConvention.StdCall)_
Public Shared Function CLSIDFromString( _
<MarshalAs(UnmanagedType.LPWStr)ByVal pwcsName As String, _
ByRef pclsid As Guid) As Integer
End Function

" active" <ac**********@a-znet.comwrote in message
news:O2*************@TK2MSFTNGP05.phx.gbl...

>GetLastWin32Error exposes the Win32 GetLastError API method from
Kernel32.DLL. This method exists because it is not safe to make a direct
platform invoke call to GetLastError to obtain this information. If you
want to access this error code, you must call GetLastWin32Error rather
than writing your own platform invoke definition for GetLastError and
calling it. The common language runtime can make internal calls to APIs
that overwrite the operating system maintained GetLastError.

You can only use this method to obtain error codes if you apply the
System.Runtime.InteropServices.DllImportAttribu te to the method signature
and set the SetLastError field to true. The process for this varies
depending upon the source language used: C# and C++ are false by default,
but the Declare statement in Visual Basic is true. For additional
information about the GetLastError and SetLastError Win32 API methods,
see the MSDN Library.

What does the last paragraph mean?

Especially the "...only...if you apply the ..." part

What Declare are they taking about?

I'd like to messagebox only if there is an error.

How can I test for success/failure?

Thanks a lot

[Armin Zingler]

" active" <ac**********@a-znet.comschrieb

GetLastWin32Error exposes the Win32 GetLastError API method from
Kernel32.DLL. This method exists because it is not safe to make a
direct platform invoke call to GetLastError to obtain this
information. If you want to access this error code, you must call
GetLastWin32Error rather than writing your own platform invoke
definition for GetLastError and calling it. The common language
runtime can make internal calls to APIs that overwrite the operating
system maintained GetLastError.

You can only use this method to obtain error codes if you apply the
System.Runtime.InteropServices.DllImportAttribute to the method
signature and set the SetLastError field to true. The process for
this varies depending upon the source language used: C# and C++ are
false by default, but the Declare statement in Visual Basic is true.
For additional
information about the GetLastError and SetLastError Win32 API
methods, see the MSDN Library.

What does the last paragraph mean?

Especially the "...only...if you apply the ..." part

What Declare are they taking about?

Declare Sub bla Lib "kernel32.dll" ()
The paragraph says that calling GetLastWin32Error only makse sense if the
API function called is declared using the DllImportAttribute while
specifying SetLastError=True. It depends on the language how this can be
done. In VB, you have two ways to declare an external function:

- Using the DllImport attribute
- Using the Declare statement (as shown above)

It says that, using the Declare statment, the SetLastError field is set to
True by default, so you don't have to (or can't) explicitly set it to true.

I'd like to messagebox only if there is an error.

How can I test for success/failure?

If you used the Declare statement for declaring the function called, simply
call GetLastWin32Error afterwards. Nothing else has to be done.

If you used the DllImportAtribte for declaring the function, you must set
SetLastError = True in the declaration:

<DllImportAttribute("kernel32.dll", setlasterror:=True)_
Shared Sub bla()
End Sub
Armin

[active]

>The functions themselves return success or failure.

I was thinking that if I called GetLastWin32Error when there was no error
the return might indicate that fact.

thanks

[active]

>>

>You can only use this method to obtain error codes if you apply the
System.Runtime.InteropServices.DllImportAttribu te to the method
signature and set the SetLastError field to true. The process for
this varies depending upon the source language used: C# and C++ are
false by default, but the Declare statement in Visual Basic is true.
For additional
information about the GetLastError and SetLastError Win32 API
methods, see the MSDN Library.

What does the last paragraph mean?

Especially the "...only...if you apply the ..." part

What Declare are they taking about?

Declare Sub bla Lib "kernel32.dll" ()

>>
What Declare are they taking about?

Declare Sub bla Lib "kernel32.dll" ()

I was trying to turn the "SetLastError field to true" into a statement about
GetLastWin32Error. Not too bright!
How about your example above.
"kernel32.dll" is just an example?
GetLastWin32Error applies to other dll's, right?
Thanks

[active]

So it's not VB vs c#, it's vb's Declare vs vb or C# DllImportAttribute
thanks

>
If you used the Declare statement for declaring the function called,
simply
call GetLastWin32Error afterwards. Nothing else has to be done.

If you used the DllImportAtribte for declaring the function, you must set
SetLastError = True in the declaration:

<DllImportAttribute("kernel32.dll", setlasterror:=True)_
Shared Sub bla()
End Sub
Armin

[Armin Zingler]

" active" <ac**********@a-znet.comschrieb

>
What Declare are they taking about?

Declare Sub bla Lib "kernel32.dll" ()

I was trying to turn the "SetLastError field to true" into a
statement about GetLastWin32Error. Not too bright!

Sorry, I don't understand.

How about your example above.
"kernel32.dll" is just an example?
GetLastWin32Error applies to other dll's, right?

Right.
Armin

[Herfried K. Wagner [MVP]]

" active" <ac**********@a-znet.comschrieb:

How about your example above.
"kernel32.dll" is just an example?
GetLastWin32Error applies to other dll's, right?

Yes, to all DLLs setting Win32 error codes, such as the system DLLs
"kernel32.dll", "gdi32.dll", ...

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[active]

thanks

"Armin Zingler" <az*******@freenet.dewrote in message
news:u8**************@TK2MSFTNGP05.phx.gbl...

>" active" <ac**********@a-znet.comschrieb

>
What Declare are they taking about?

Declare Sub bla Lib "kernel32.dll" ()

I was trying to turn the "SetLastError field to true" into a
statement about GetLastWin32Error. Not too bright!

Sorry, I don't understand.

>How about your example above.
"kernel32.dll" is just an example?
GetLastWin32Error applies to other dll's, right?

Right.
Armin

[active]

thanks

"Herfried K. Wagner [MVP]" <hi***************@gmx.atwrote in message
news:%2****************@TK2MSFTNGP02.phx.gbl...

>" active" <ac**********@a-znet.comschrieb:

>How about your example above.
"kernel32.dll" is just an example?
GetLastWin32Error applies to other dll's, right?

Yes, to all DLLs setting Win32 error codes, such as the system DLLs
"kernel32.dll", "gdi32.dll", ...

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>