C / C++ / MFC Discussion Boards

David Crow1-Jul-09 5:26

1-Jul-09 5:26

Caslen wrote:
If it is my problem is there anyway to detect programatically whether a file is already open somewhere else?

Open it exclusively. All other attempts will fail.

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Re: File Sharing (not)

Caslen1-Jul-09 5:33

Caslen

1-Jul-09 5:33

CFile::shareExclusive <-- Just what I need, thanks for the pointer.

I think shareDenyWrite would be better though allowing subsequent users read only access is that correct? Does it display a message indicating read only?

Re: File Sharing (not)

Stuart Dootson1-Jul-09 6:12

Stuart Dootson

1-Jul-09 6:12

Caslen wrote:
Does it display a message indicating read only?

What is 'it'?

Anyway - don't do that, because you still have the problem of other users reading the file while you're writing to it (because file writes aren't atomic operations) and potentially getting an inconsistent view of the file. That's why you get 'single writer, multiple reader' locks for use with in-memory resources - the resource is locked exclusive while the writer's active, but otherwise, multiple people can read the resource concurrently.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: File Sharing (not)

Caslen1-Jul-09 6:18

Caslen

1-Jul-09 6:18

Stuart Dootson wrote:
What is 'it'?

If a user tries to open an already open file is a message displayed but obviously that is up to the programmer to display the message. I've been rooting through the code (not mine) and it uses IStorage objects opened with the STGM_SHARE_EXCLUSIVE flag set. Is there any condition where this might not prevent a second copy from being opened?

Re: File Sharing (not)

Stuart Dootson1-Jul-09 7:05

Stuart Dootson

1-Jul-09 7:05

Sorry, don't know - IStorage isn't something I've used

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: File Sharing (not)

David Crow1-Jul-09 7:18

David Crow

1-Jul-09 7:18

Caslen wrote:
I've been rooting through the code (not mine) and it uses IStorage objects opened with the STGM_SHARE_EXCLUSIVE flag set. Is there any condition where this might not prevent a second copy from being opened?

Yes. It prevents others from subsequently opening the object in any mode.

Re: File Sharing (not)

Caslen1-Jul-09 21:54

Caslen

1-Jul-09 21:54

I'm unsure of how the file is prevented from opening and particularly in my case where it clearly is allowed to be opened in some (but not all) cases.

On site there are several versions of software in use - it is possible that an older version does not use the STGM_SHARE_EXCLUSIVE flag. If this older version first opened the data file would the new version with the flag still be able to open it?

What about the opposite situation where the new verion opens the data file first - would the older version be 'aware' that the file is already open if it doesn't recognise the STGM_SHARE_EXCLUSIVE flag?

Thanks for your help on this.

Re: File Sharing (not)

David Crow2-Jul-09 3:55

David Crow

2-Jul-09 3:55

The file system keeps track of what files are open and with what locking/sharing attributes. When you use an API to open a file, it will ask the file system if that is currently allowable. If it's not, the API will return a value indicating such.

Re: File Sharing (not)

Caslen2-Jul-09 5:15

Caslen

2-Jul-09 5:15

Ok thats beginning to make more sense, the older version of software is probably opening the file, not marking it as open so the newer version can still open it, the newer version is modifying the data file and saving it before the older version then saves an unmodified data file. This ties in with the customers complaint that he is losing changes he's making to his files.

A couple more questions (sorry!) and probably drifting out of scope here but...

1. Would the file system itself be smart enough to know that a file has been changed since it was opened? (ie if another PC modifies the file between the first PC opening it and closing it)

2. On a typical file system would it be possible to automatically mark a file as already open?

Thanks

Steve

Re: File Sharing (not)

David Crow2-Jul-09 5:18

David Crow

2-Jul-09 5:18

Caslen wrote:
1. Would the file system itself be smart enough to know that a file has been changed since it was opened? (ie if another PC modifies the file between the first PC opening it and closing it)

No.

Caslen wrote:
2. On a typical file system would it be possible to automatically mark a file as already open?

What do you mean by "automatically?"

Re: File Sharing (not)

Caslen2-Jul-09 5:30

Caslen

2-Jul-09 5:30

When the file system receives a request to open a file it marks the file as open and refuses access to further requests to open it until the first user closes his copy. This could cause problems - what if the first user never closes the file?

Re: File Sharing (not)

David Crow2-Jul-09 5:33

David Crow

2-Jul-09 5:33

Caslen wrote:
what if the first user never closes the file?

Then subsequent requests will fail.

Class Template in Visual C++

emira671-Jul-09 4:32

emira67

1-Jul-09 4:32

Hello,

I formed class template that represent two dimensional array :

template<class T>
class Array2D {
protected:  

public:
      T *data;

        const unsigned rows, cols, size;
        Array2D(unsigned r, unsigned c) : rows(r), cols(c), size(r*c) {

      data = new T[size];
        }
        ~Array2D() { delete data; }
        void setValue(unsigned row, unsigned col, T value) { 
                data[(row*cols)+col] = value;
        }
        T getValue(unsigned row, unsigned col) const {
                return data[(row*cols)+col];
        }
};

And one dimensional data array is present:

array<double>^ input={20,4,6,15,7,2,1,8,9};

I have function it's inputs are class template and one dimensional data array.I set one dimensional array values to class template :

void function(Array2d<double> &x,array< double>^ input,int width,int,height)
{


double temp;
temp1=0;

double temp2;

int i,j;

// assign input array values to two dimensional array
for(i=0;i<width;i++)
for(j=0;j<height;j++)
{
{ temp2=input[temp1];
  x.setvalue(i,j,temp2);
  temp1=temp1+1;
}
}

}

After all I declared 3x3 class template:

Array2D<double>A(3,3);

I sent it to function:

function(A,input,3,3);

And I tried to print Array2D values:

double temp;
for(i=0;i<3;i++)
for(j=0;j<3;j++)
{
{temp=A.getValue(i,j)

Console:Write("{0}",temp);}}

I executed this applicaiton in CLR Application in Visual Studio 2008 amd it worked .But I want to implement this code on Windows Form Application,and it gave error like these on Form Application:

error C2065: 'Array2D' : undeclared identifier
error C2065: 'A' : undeclared identifier

How can I overcome this error or where should I locate class template?

Best Regards...

Re: Class Template in Visual C++

led mike1-Jul-09 4:40

led mike

1-Jul-09 4:40

emira67 wrote:
error C2065: 'Array2D' : undeclared identifier
error C2065: 'A' : undeclared identifier

If you don't know how to resolve those compiler errors then you are attempting something that is beyond your current C++ programming capacity. You need to go back to basics and learn more about them before you move on to more advanced subjects.

Also I do not recommend moving on to using C++/CLI (managed or mixed mode) until you have a firm grasp of C++.

Re: Class Template in Visual C++

David Crow1-Jul-09 4:47

David Crow

1-Jul-09 4:47

emira67 wrote:
How can I overcome this error...

You might want to ask in the proper forum. Those that are in the know may not see it otherwise.

Re: Class Template in Visual C++

Stuart Dootson1-Jul-09 4:58

Stuart Dootson

1-Jul-09 4:58

Remember what I told you before[^]?!

emira67 wrote:
In fact I declared this items!!!

But obviously not somewhere that the code that used the items was able to see them.

emira67 wrote:
Could you help me please?

If you posted some more detail (the filename that you put the template class & function declaration in, the code that uses the matrix and function), then possibly. However, your code is syntactically and semantically correct - you've just organised it so that the code that uses those things can't see them. Check through your code to understand why!

Guess what - it still applies.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

dll function call in vc++2008 clr bse apllication

PIYUSH19661-Jul-09 4:08

PIYUSH1966

1-Jul-09 4:08

I am new for vc++, i am doing project on vc++2008 clr base windows form application. not able to use inpout.dll in my project please help. if possible give example. thanks

Re: dll function call in vc++2008 clr bse apllication

led mike1-Jul-09 4:35

led mike

1-Jul-09 4:35

PIYUSH1966 wrote:
not able to use inpout.dll in my project

Do you mean inpout32.dll[^]?

PIYUSH1966 wrote:
if possible give example

You mean like the free for download example from the site where you get the DLL?

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Hadi Dayvary1-Jul-09 3:49

Hadi Dayvary

1-Jul-09 3:49

Hi I have written a downloader program with MFC classes : CInternetSession/CHttpConnection/CHttpFile
It works just fine,
But now I want to change it so it can download from sharing web sites like RAPIDSHARE
I tried these ways to send the username & password to the web site:

1. pInternetSession->GetHttpConnection(sServer, nPort, sUser, sPassword);
2. pInternetSession->GetHttpConnection(sUser + _T(":") + sPassword + _T("@") + sServer, nPort);
3. pFile->AddRequestHeaders(Base64Coder(_T("Authorization: Basic ") + sUser + _T(":") + sPassword));

But none of them worked!!! (I have searched a lot but I did not find any other way yet!)

Any other idea!

Regrads
Hadi

www.logicsims.ir

MFC CSocket class!

Hadi Dayvary1-Jul-09 3:47

Hadi Dayvary

1-Jul-09 3:47

Hi I have a client/server project with MFC class CSocket.
Everything is ok except that SOMETIMES client sends a request(a structure) to the server but the server DOES NOT take it!
I put a lot of TRACE and message boxes and I'm sure all my codes is ok (more than 20 times runs ok, but after that it just hangs!)
I also tested the MFC sample : chatsrvr/chatter program, if you type some chars and press enter quickly, after 5 or 10 lines the server will not get any more data!!!
Is there any bug or trick or something out there!?
Regrads
Hadi

www.logicsims.ir

Re: MFC CSocket class!

led mike1-Jul-09 4:28

led mike

1-Jul-09 4:28

Hadi Dayvary wrote:
Is there any bug or trick or something out there!?

There are so many bugs it's incredible. However almost every one of them is a bug in the code written by people like me and you.

The trick to Server development is to learn multi-threading, it's not easy. The trick to Server Socket development is to learn the first trick and then learn Socket development, which again is not that easy.

Re: MFC CSocket class!

Hadi Dayvary1-Jul-09 5:16

Hadi Dayvary

1-Jul-09 5:16

My code is completly multithread,
As I said I have tested some other example (like the one in MSDN) and they have this problem too.

www.logicsims.ir

Re: MFC CSocket class!

led mike1-Jul-09 5:39

led mike

1-Jul-09 5:39

Ok, good luck.

Re: MFC CSocket class! [modified]

Moak18-Jul-09 4:36

Moak

18-Jul-09 4:36

Consider using CAsyncSocket if it has to be MFC based, do not use CSocket. Also see http://tangentsoft.net/wskfaq/articles/csocket.html[^] and for some more low-level background Beej's Guide to Network Programming[^]

/M

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modified on Saturday, July 18, 2009 10:42 AM

Re: MFC CSocket class!

Hadi Dayvary18-Jul-09 5:14

Hadi Dayvary

18-Jul-09 5:14

Thank you so much

www.logicsims.ir

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