Re: computer name length issue - C / C++ / MFC Discussion Boards

George_George16-Dec-08 2:08

16-Dec-08 2:08

Thanks CPallini!

My question is whether there is a macro which represents the max machine name length -- I need such macro to define buffer length to retrieve machine name using this API. Any comments?

If there is not such a built-in macro, I am not sure whether use 255? 1024 or something else is better?

regards,
George

Re: computer name length issue

Randor 16-Dec-08 2:02

Randor

16-Dec-08 2:02

George_George wrote:
Any macro used to represent computer name max length

I don't know if there is a #define available for this DNS limit. But RFC-2181 Section 11. - Name syntax
[^] states that the maximum length of the entire DNS record is 255 bytes/octets with each section limited to 64 bytes including the separator which would be 63 usable characters. You should be safe declaring a buffer 64 characters which would include the NULL terminator.

George_George wrote:
MAX_COMPUTERNAME_LENGTH is too small and just 15 characters.

Thats because its the NetBios name limit, a Microsoft invention which has nothing to do with the DNS hostname.

One last note.. if you want to support international domain names[^] you should declare your buffer as wchar_t. The same maximum length restrictions apply.

Best Wishes,
-David Delaune

Re: computer name length issue

George_George16-Dec-08 2:10

George_George

16-Dec-08 2:10

Thanks for your advice, David!

Let us looking forward to finding whether someone here has good knowledge whether there is such a built-in macro? Smile | :)

regards,
George

Re: computer name length issue

Randor 16-Dec-08 2:34

Randor

16-Dec-08 2:34

Found them in the Platform SDK file:

#include <Windns.h>

You will find:

//
//  DNS Names limited to 255, 63 in any one label
//

#define DNS_MAX_NAME_LENGTH             (255)
#define DNS_MAX_LABEL_LENGTH            (63)

#define DNS_MAX_NAME_BUFFER_LENGTH      (256)
#define DNS_MAX_LABEL_BUFFER_LENGTH     (64)

Best Wishes,
-David Delaune

Re: computer name length issue

George_George17-Dec-08 2:05

George_George

17-Dec-08 2:05

Cool, David!

I think I should use 64. Smile | :)

regards,
George

Re: computer name length issue

Luc Pattyn16-Dec-08 2:45

Luc Pattyn

16-Dec-08 2:45

Hi George,

the answer is no; there is no macro/constant giving max length.
However there is a Win32 function that gives you the max length, it is called GetComputerNameEx; just give it a buffer=NULL and a size variable whose value is set to zero. Upon return, read that very same size value, then allocate a sufficiently large buffer, and call GetComputerNameEx again.

BTW: this is a common pattern in Win32: first ask for size, then allocate, then ask for data using the same function.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Fixturized forever. Confused | :confused:

Re: computer name length issue

George_George17-Dec-08 1:55

George_George

17-Dec-08 1:55

Thanks Luc,

I am just surprised there is no such macro defined on Windows as built-in macro. Smile | :)

regards,
George

Re: computer name length issue

Luc Pattyn17-Dec-08 2:27

Luc Pattyn

17-Dec-08 2:27

Some parameters just aren't constant, e.g. they depend on installation choices, available hardware, etc. In these cases you need to actually run some code to determine maximum sizes. Not sure why it would be dynamic in this case, but that is the author's decision after all.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

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Re: computer name length issue

George_George17-Dec-08 2:30

George_George

17-Dec-08 2:30

Macro exists. Here it is.

http://www.codeproject.com/script/Forums/View.aspx?fid=1647&msg=2846296[^]

regards,
George

Re: computer name length issue

Luc Pattyn17-Dec-08 2:34

Luc Pattyn

17-Dec-08 2:34

OK.
does it match the return value when size zero was given?

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Fixturized forever. Confused | :confused:

Re: computer name length issue

George_George17-Dec-08 2:43

George_George

17-Dec-08 2:43

What do you mean match return value? Return value is BOOL. Smile | :)

http://msdn.microsoft.com/en-us/library/ms724301(VS.85).aspx[^]

regards,
George

Re: computer name length issue

Mark Salsbery16-Dec-08 5:37

Mark Salsbery

16-Dec-08 5:37

Your answer is in the link YOU provided

"The length of the name may be greater than MAX_COMPUTERNAME_LENGTH
characters because DNS allows longer names. To ensure that this buffer
is large enough, set this parameter to NULL and use the required buffer
size returned in the lpnSize parameter."

As many others have mentioned, that's the proper way to use the API.

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: computer name length issue

George_George17-Dec-08 1:59

George_George

17-Dec-08 1:59

Thanks Mark!

You mean call this API twice? I showed my understanding of your points in the following pseudo code. Any comments? Does it what you mean?

int size;

GetComputerNameEx(
  __in     COMPUTER_NAME_FORMAT NameType,
   NULL,
  &size
);

buffer = new char[size+1];

GetComputerNameEx(
  __in     COMPUTER_NAME_FORMAT NameType,
   buffer,
  &size
);

regards,
George

Re: computer name length issue

Mark Salsbery17-Dec-08 5:00

Mark Salsbery

17-Dec-08 5:00

George_George wrote:
You mean call this API twice?

Yes.

You may want to increment the size variable before the second call...

int size = 0;

GetComputerNameEx(
  __in     COMPUTER_NAME_FORMAT NameType,
   NULL,
  &size
);

size++;
buffer = new char[size];

GetComputerNameEx(
  __in     COMPUTER_NAME_FORMAT NameType,
   buffer,
  &size
);

Many APIs were designed to be called that way.

If you absolutely must use a static buffer length, in my experience,
a buffer size of 260 (MAX_PATH) has always been large enough.
Doing it as shown above is the safe, correct way, however.

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

Re: computer name length issue

George_George17-Dec-08 19:36

George_George

17-Dec-08 19:36

Thanks Mark,

Here is a better solution. Using built-in macro. Any comments?

http://www.codeproject.com/script/Forums/View.aspx?fid=1647&msg=2846296[^]

regards,
George

VLCPlugin2 - Snapshot

kutti16-Dec-08 0:44

kutti

16-Dec-08 0:44

Hi,

I am using VLC plugin 2 Active X control in vc++ sample application.

I can able to see live video, using CVLCPlaylist.add() method call.
How to take snapshot?
Any help ?

Re: VLCPlugin2 - Snapshot

Eytukan16-Dec-08 6:29

Eytukan

16-Dec-08 6:29

printscreen button Roll eyes | :rolleyes:

OK,. what country just started work for the day ? The ASP.NET forum is flooded with retarded questions. -Christian Graus

Best wishes to Rexx[^]

Re: VLCPlugin2 - Snapshot

kutti16-Dec-08 17:27

kutti

16-Dec-08 17:27

Hi,
Thanks for your reply.

how to set the snapshot path?
is there any default path for snapshot?

I tried your suggestion for taking snapshot.
But it is not working.
Is there any possibility to use CVLCVideo::takeSnapshot() ?

Inheritance in C

Chandrasekharan P15-Dec-08 23:39

Chandrasekharan P

15-Dec-08 23:39

I dont know if this is the right forum to post this query

i wanted to know if we can achieve inheritance and encapsulation in C.

Re: Inheritance in C

Stuart Dootson15-Dec-08 23:50

Stuart Dootson

15-Dec-08 23:50

With some effort, you can mimic inheritance.

Use of structs effectively gets you encapsulation.

Re: Inheritance in C

Chandrasekharan P15-Dec-08 23:54

Chandrasekharan P

15-Dec-08 23:54

a little more explanation will be of great help.

Re: Inheritance in C

David Crow16-Dec-08 2:40

David Crow

16-Dec-08 2:40

struct base<br />
{<br />
};<br />
<br />
struct derived : public base<br />
{<br />
};

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

Re: Inheritance in C

C^hris L^osinger16-Dec-08 6:37

C^hris L^osinger

16-Dec-08 6:37

? struct derived : public base

that is not C

image processing toolkits | batch image processing

Re: Inheritance in C

David Crow16-Dec-08 8:25

David Crow

16-Dec-08 8:25

I see that I failed to see that the OP wanted a solution in C. D'Oh! | :doh:

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

Re: Inheritance in C

CPallini16-Dec-08 0:03

CPallini

16-Dec-08 0:03

Why don't you use C++, instead?

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

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