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sweety1988 wrote: what is the best answer to tell if I asked for my experience in the last project
The truth
I know the language. I've read a book. - _Madmatt
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Now there's a novel concept.
"WPF has many lovers. It's a veritable porn star!" - Josh Smith As Braveheart once said, "You can take our freedom but you'll never take our Hobnobs!" - Martin Hughes.
My blog | My articles | MoXAML PowerToys | Onyx
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You're going to get any questions they feel like asking. There is no predicting, no standard set of questions. Either you know this stuff or you don't.
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- any questions about things you have real experience with: tell a convincing story, not too technical, make your experience stand.
- be honest about experience you don't have. They will find out if your not honest. Tell them that you are a fast learner and that you will learn it quickly - even if you hesitate yourself on that.
- realize that someone who has all the experience they ask for probabilly don't wants the job because it has no challenge anymore for him.
- answer any non-technical question in a non-technical way. Reply to direct technical questions in a technical way. Be to the point and ask if your answer is enough.
- only speak about negative aspects of your current job in a general way: they don't want to know the nasty details.
- Know the company, try to understand what they want to achieve with you, participate on that. Realize that their goals mostly will not be: technical goals but bussiness goals.
- Try to find out who is the most important of the people you speak. Make sure he/she has a possitive impression of you, but don't forget the others.
And last the best tip i ever had:
Sit, speak and be there like you would be if you already had the job.
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Is there any .Net framework classes which deal in file associations ? I am looking for the .Net equivalent of the Win32 shell functions "AssocQueryString" and "FindExecutable".
Edward Diener
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Edward Diener wrote: Is there any .Net framework classes which deal in file associations
No.
Edward Diener wrote: I am looking for the .Net equivalent of the Win32 shell functions "AssocQueryString" and "FindExecutable".
There are no managed code versions of these functions.
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Hi,
I want to use a simple function in a C++ DLL. The declaration in the header file for that function is:
#define API_SPEC __declspec(dllexport)
void API_SPEC API_getApiVersion (std::wstring *version)
That function receive a pointer to a UNICODE string and will put the release ID of that API in that string. (correct me if i'm wrong!)
I use VB.Net to call that DLL and read the content of that string. Here is my code:
Public Class Form1
<DllImport("C:\Api.dll", EntryPoint:="?API_getApiVersion@@YAXPAV?$basic_string@GU?$char_traits@G@std@@V?$allocator@G@2@@std@@@Z", CallingConvention:=CallingConvention.ThisCall, CharSet:=CharSet.Unicode)> _
Public Shared Sub test(ByVal version As String)
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim theVersion As String = New String(" "c, 20)
Call test(theVersion )
MessageBox.Show(theVersion)
End Sub
End Class
When I run that code I get:"AccessViolationException was unhandled."
My question: what is wrong with my code? I even try to use a stringbuilder instead of string type but I got the same error.
Thanks for your help!
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Hi,
I don't have the full answer, however here are some pointers:
1.
IMO for writable strings you must use a StringBuilder, give it sufficient capacity, pass it on, then convert it to a string using ToString()
2.
your entypoint seems very bizarre, and way too long. I suggest you check it, perhaps using DUMPBIN/EXPORT
3.
I have an unfinished article[^]dealing with P/Invoke, maybe that can help you.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that. [The QA section does it automatically now, I hope we soon get it on regular forums as well]
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Thanks Luc, I will have a look to your article.
I took the entrypoint name using DUMPBIN /EXPORT.
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Following on from Luc's comment, your exported function name is in C++ format, it should be C. Change your header file to put extern "C" { in front of the definition and } after it, and you should get exported as written.
MVP 2010 - are they mad?
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Richard, do you mean that because the DLL has been written in C++ it can't be exported to DotNet? 
That I lost a week trying to find a solution when there is not that way? 
Unfortunately, because the DLL is from a third party, I can't recompile to change the export statement.
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TremaHD wrote: do you mean that because the DLL has been written in C++ it can't be exported to DotNet?
Not quite, it's just that the usual method is to export class/method names in clear "C" format rather than C++. I think you should still be able to use it, but you probably need the documentation that should come with it. If it's a third party DLL then you should approach the supplier/writer first.
[edit]Also I do not think that you can pass a .NET String reference as a std::wstring pointer.[/edit]
MVP 2010 - are they mad?
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Thanks Richard and Luc for your replies, really appreciated!
Richard, for the string type I agree with you, that's why I tried a Stringbuilder type instead, but no more result.
About the documentation, I though that the header file of the API was enough (.h file). I also have a .lib file but I think that is for C++ so not useful for me with Dot Net. What else could have been useful?
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Your original post shows the following extract from the header file:
#define API_SPEC __declspec(dllexport)
void API_SPEC API_getApiVersion (std::wstring *version)
Since you cannot directly convert a VB.NET String to a C++ std::wstring* I think the only solution is to write a C++ interface that can take a pointer to a StringBuilder object. This code could then call the API passing a pointer to a std::wstring which it will copy to the StringBuilder before returning to the VB.NET code.
Comments, Luc?
MVP 2010 - are they mad?
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Hello all,
I think the solution here is to use the COM interoperability provided by dotNET. Note that I have not yet tried this myself, but I believe you have to use MarshallAs to ensure that VB.NET, in this case, converts the string before the call to a LPWSTR and after the call converts it back to a VB string.
Whether you have to use a stringbuilder or a string here I'm not sure, but my best guess is that you can use a normal string.
Here's a msdn link that might help, though it's not entirely clear to me:
http://msdn.microsoft.com/en-us/library/s9ts558h(VS.71).aspx
I'm not currently in a position to access VB.NET (or any other .NET language for that matter), so I'm sorry I can't give you the complete code.
Maybe one of the other repliers can help you out more.
Good Luck,
MicroVirus
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The link provide good information and I tried but what I got is a Debug Assertion Failed box on the expression: _CrtIsValidHeapPointer(pUserData) 
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MicroVirus wrote: I think the solution here is to use the COM interoperability provided by dotNET.
He is already using that. The problem is that the C++ library function expects as input parameter a std::wstring* and I don't think there is any marshalling for such a class, so there has to be a user written intermediate function that accepts a char/byte[] and converts to and from the string class.MVP 2010 - are they mad?
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Ouch right... I obviously overlooked that :S
In that case you're absolutely right and a wrapper needs to be written. Easiest way is to do that in (unmanaged) C++. I'd suggest taking the Windows API path on this one and write a function that takes a LPWSTR and size of the buffer, and returns the result of the function you are trying to access in this buffer.
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As I recommended a few days ago!
<i>MVP 2010 - are they mad?</i>
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AFAIK all extern 'C' does is tell the C++ compiler not to mangle the method names, which makes it easier to get the P/Invoke entrypoint right. Real C++ code can be P/Invoked without problems.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that. [The QA section does it automatically now, I hope we soon get it on regular forums as well]
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Any comments on my latest, above?
MVP 2010 - are they mad?
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Hi Richard,
AFAIK and assuming std::wstring is just Unicode, the DllImport attribute needs a Charset.Unicode (or the Declare statement needs a Unicode keyword), as ANSI is the default marshaling for strings.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that. [The QA section does it automatically now, I hope we soon get it on regular forums as well]
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Hi Luc,
I haven't done a lot of work in this area but std::wstring is a C++ class that holds a Unicode string. I'm not sure whether the marshalling can handle it directly, so I may try some experiments to see what I can discover.
MVP 2010 - are they mad?
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Hi guys,
After reading Luc's article (by the way, very interesting) and reading your posts, I tried to change the string type to Stringbuilder type. Because the C++ DLL sub has an OUT parameter, I modified the declaration to pass my variable byRef instead of ByVal:
<DllImport("C:\Api.dll", EntryPoint:="?API_getApiVersion@@YAXPAV?$basic_string@GU?$char_traits@G@std@@V?$allocator@G@2@@std@@@Z", CallingConvention:=CallingConvention.ThisCall, CharSet:=CharSet.Unicode)> _
Public Shared Sub test(ByRef version As StringBuilder)
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim theVersion As StringBuilder = New Stringbuilder(20)
Call test(theVersion )
MessageBox.Show(theVersion.tostring)
End Sub
End Class
What is happening now is that when the line 'Call test(theVersion)' is executed, the application quit without any warning or error, even if I put a breakpoint at the 'Messagebox.show' line. Am I right to pass my variable byRef instead of byVal. Of course, I tried to change it to use byVal and what i get is an empty string in return.
When you look at the declaration line in the C++ code there is that #DECLARE API_SPEC line and that API_SPEC is also at the beginning of the method API_getApiVersion. Most of the time the DECLARE statement for __declspec(dllexport) use the C or C++ keyword to specify the language type. Here I have a keyword that is use at the beginning of the method definition. What is the purpose of that declare then?
Thanks again.
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Hi,
yes ByRef seems right.
I'm still not happy with your entrypoint, "char_traits" and "allocator" don't belong there AFAIK.
I just now noticed ThisCall, which probably is wrong.
suggestion: if you have the source to the DLL, and can build it again, you could add a method that does what you need, with whatever API you choose. That one could have extern 'C' (hence no mangling), an explicit calling convention, and fill or return a regular string.
Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles]
I only read code that is properly formatted, adding PRE tags is the easiest way to obtain that. [The QA section does it automatically now, I hope we soon get it on regular forums as well]
modified on Friday, February 5, 2010 9:08 AM
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