C / C++ / MFC Discussion Boards

The program reads and writes hard disk in a thread heavily, how to make it work when idle?

followait1-Jan-09 18:07

1-Jan-09 18:07

The program do a lot of hard disk reading and writing,
so other application became very slow,
any way to make it work when the hard disk is not busy?

Re: The program reads and writes hard disk in a thread heavily, how to make it work when idle?

Jijo.Raj1-Jan-09 23:57

Jijo.Raj

1-Jan-09 23:57

My suggestion is to use Memory Mapped Files[^]. It will definitely improve the file access performance. You can use CMemMapFile[^] class for making your task easier.

Just try it and check whether the MemoryMapped files improves the performance in your case. Good Luck!

Regards,
Jijo.

_____________________________________________________

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Multithreading

hrishiS1-Jan-09 18:00

hrishiS

1-Jan-09 18:00

Hi Experts,
I am learning threading concept in vc++. I have gone through the basics.
I would like to clear my doubts for the following.

1. when do we used
. a. afxBeginthread
. b. beginThread
. c. createThread

2. to communicate between different threads

3. thread synchronisation.

Could u please advice me any link (or if I can get any documents) from where I can learn the same ( specially for point 2 and 3 )

Thank You So much in advance
Himangshu
Bangalore

Re: Multithreading

Hamid_RT1-Jan-09 18:09

Hamid_RT

1-Jan-09 18:09

See C++ Multithreading Tutorial[^].

Of one Essence is the human race
thus has Creation put the base
One Limb impacted is sufficient
For all Others to feel the Mace
(Saadi )

Re: Multithreading

hrishiS1-Jan-09 18:18

hrishiS

1-Jan-09 18:18

thax a lot for ur reply hamid....I will go through it and post here again

Re: Multithreading

hrishiS1-Jan-09 18:30

hrishiS

1-Jan-09 18:30

Hi hamid,

Its a perfect docs. But, I guess it gives the details of threads and synchronisation mechanism...Can u pls advice anything from where I will get the details of communication between thread?

Thx
Himangshu

Re: Multithreading

Roger Stoltz1-Jan-09 22:17

Roger Stoltz

1-Jan-09 22:17

You'll find everything you need to know here[^].

"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown

Buffer?

dec821-Jan-09 16:46

dec82

1-Jan-09 16:46

char buffer[] = "This is a test of the memset function";

Could help me to explain this declaration: why char, but buffer is assigned to a string?
Thanks

Re: Buffer?

«_Superman_»1-Jan-09 17:54

«_Superman_»

1-Jan-09 17:54

the [] indicates an array.
So it is an array of characters.
Which means string.

« Superman »

Re: Buffer?

Hamid_RT1-Jan-09 18:17

Hamid_RT

1-Jan-09 18:17

c++ arrays are declare with [] and data type like this when you use of this code this char array can be use as a string and you initialization without any size.

Of one Essence is the human race
thus has Creation put the base
One Limb impacted is sufficient
For all Others to feel the Mace
(Saadi )

Re: Buffer?

Michael Dunn2-Jan-09 13:17

Michael Dunn

2-Jan-09 13:17

Because in C, a "string" is just an array of char that ends with a '\0' character. There are some instances (this being one of them) when a string literal and an array of char are compatible types.

--Mike--
Visual C++ MVP Cool | :cool:

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Vista magnification API

Hans Dietrich1-Jan-09 13:46

Hans Dietrich

1-Jan-09 13:46

Does anyone have a sample program (+ source code) that uses the Vista magnification APIs? Or a link to such a sample program? I'm looking for a working sample program, not the docs for the API.

Best wishes,
Hans

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Emergence! 0xC0000005: Access Violation again [modified]

whiteclouds1-Jan-09 12:57

whiteclouds

1-Jan-09 12:57

Hi, thomas!
Thanks for your reply.
I think I had found the reason. After I delete some variables that aren't be used any more, the exception is missing. But another exception is occur same as this when I use the code following:

time_t  ltime;      // local time
struct tm *gmt; // Greenwich Mean Time
png_time ttime; // png format
time (&ltime);  // get the local time---EXCEPTION 0xC0000005 OCCUR HERE!
gmt = gmtime (&ltime);  // convert to gmt
png_convert_from_struct_tm (&ttime, gmt);  // convert to png format
        png_set_tIME (png_ptr, info_ptr, &ttime);

I trace this exception into MFC and I found when a function named _mlock was invoked in the __tzset function, the exception occur. The related code like this:

_mlock( _TIME_LOCK );

I don't know the reason and hope you or others can give me some suggestion. Thank you!
By the way: if the title of this message offend someone, I'm very sorry because this event is an emergency really. Mad | :mad:

Regards!

whiteclouds

modified on Thursday, January 1, 2009 8:20 PM

Re: Emergence! 0xC0000005: Access Violation again

Luc Pattyn1-Jan-09 13:11

Luc Pattyn

1-Jan-09 13:11

Hi,

0xC0000005 is an access or privilege violation, which means you can't access something;
quite often it indicates an invalid pointer, such as NULL. It could also mean you don't
have the required privileges to do something.

suggestion: look at your source code, and all the variables that appear in the line that fails.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Love, happiness and fewer bugs for 2009!

Re: Emergence! 0xC0000005: Access Violation again

whiteclouds1-Jan-09 14:20

whiteclouds

1-Jan-09 14:20

Hi
I can't get your meaning. I check my code again. The address of the variable ltime is valid. All things looks like in order. But the error always occur. Frown | :(

Help!

Regards!

whiteclouds

Re: Emergence! 0xC0000005: Access Violation again

Luc Pattyn1-Jan-09 14:48

Luc Pattyn

1-Jan-09 14:48

Maybe this is relevant[^]?

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Love, happiness and fewer bugs for 2009!

Re: Emergence! 0xC0000005: Access Violation again

whiteclouds3-Jan-09 14:54

whiteclouds

3-Jan-09 14:54

I think I had resolved this problem. My solution is to instead the time_t with SYSTEMTIME structure. Then everything looks right. Otherwise I don't know the detail of it. I think maybe this structure was obsoleted. Smile | :)

Re: Emergence! 0xC0000005: Access Violation again

Luc Pattyn3-Jan-09 15:50

Luc Pattyn

3-Jan-09 15:50

Glad you got it working.
Thanks for sharing this.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

Love, happiness and fewer bugs for 2009!

Menu Items

BobInNJ1-Jan-09 11:09

BobInNJ

1-Jan-09 11:09

I am developing an application using C++ and MFC. Please consider the following code from a Windows RC (Resource Script) file:

<br />
<br />
IDR_MAINFRAME MENU<br />
BEGIN<br />
    POPUP "&File" {<br />
        MENUITEM "&New",                CALC_FILE_NEW<br />
        MENUITEM "Calculate"            CALCULATE<br />
        MENUITEM "Abort Calculation"    ABORT_CALCULATION,GRAYED<br />
        MENUITEM "&Exit",               CALC_FILE_EXIT<br />
    }<br />
    .<br />
    .<br />
    .<br />

I would expect the third menu selection to be grayed out. That is, the user should not be able to select it. However, this is not what happens. I would like to know why?

Thanks

Bob

Re: Menu Items

Richard Andrew x641-Jan-09 11:27

Richard Andrew x64

1-Jan-09 11:27

I think you also have to specify that it's disabled as well.

Re: Menu Items

BobInNJ1-Jan-09 12:31

BobInNJ

1-Jan-09 12:31

Richard,

Thanks for the response. However, I do not think DISABLED is a valid option for creating the menu item. When I tried it, it would not going through the resource compiler. The line I tried
was:

<br />
        MENUITEM "Abort Calculation"    ABORT_CALCULATION,GRAYED,DISABLED<br />

Was that what you meant?

Bob

Re: Menu Items

Richard Andrew x641-Jan-09 12:35

Richard Andrew x64

1-Jan-09 12:35

You're right. I checked the docs, and the word I was thinking of is "INACTIVE", not "disabled".

However, it says that GRAYED should do what you are looking for.

Can you say what behavior you are observing when you use just GRAYED?

Re: Menu Items

BobInNJ1-Jan-09 12:40

BobInNJ

1-Jan-09 12:40

Richard,

What I would like is the menu option to be set in such a way that the user cannot select it. In addition, when the menu is displayed, it should be displayed in such a way that it looks disabled to the user.

Thanks

Bob

Re: Menu Items

Richard Andrew x641-Jan-09 12:39

Richard Andrew x64

1-Jan-09 12:39

I see that you are missing commas in a couple of locations in your MENUITEM list.

Perhaps that is the cause of the malfunction?

You're missing commas on the Calculate and Abort Calculation menu items.

Re: Menu Items

BobInNJ1-Jan-09 12:56

BobInNJ

1-Jan-09 12:56

Richard,

Thanks for the response. I tried adding those missing commas as you suggested but it did not solve my problem.

Bob

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