C / C++ / MFC

13-Apr-06 19:53

Hi all.
I have this code:

//an object, create as<br />
MObject* object = new MObject();<br />
object->value=10;<br />
//try to delete to delete memory of this object<br />
delete object;<br />
//and then check it<br />
<br />
//this object is not NULL<br />
if (object!=NULL){<br />
//its memory is deleted, so below command is error, how to catch this error by<br />
//try{}catch("what is here"){}, or have other way to catch this error?<br />
    int j=object->value;<br />
........<br />
}

Please help me.
Thanks

Shuang. Wu13-Apr-06 20:10

Shuang. Wu

13-Apr-06 20:10

try{
int j = object->value;
}
catch(...){
// handling here
}

<font=sans-serif>|-|3llo Wo|2ld

pjmvn13-Apr-06 20:14

13-Apr-06 20:14

Shuang. Wu wrote:
try{
int j = object->value;
}
catch(...){
// handling here
}

Thanks, but this does not work.
I using VC++ 2005.

Shuang. Wu13-Apr-06 20:46

Shuang. Wu

13-Apr-06 20:46

well, the code
int j = object->value;
could lead an unexpected result. sometimes exceptions like AV(Access Violation) could be thrown out, but not always.

<font=sans-serif>|-|3llo Wo|2ld

Stephen Hewitt14-Apr-06 21:31

Stephen Hewitt

14-Apr-06 21:31

In general catch(...) is bad form. A general rule of exception handling is that you should only catch what you expect to be thrown.

Steve

Steve Echols13-Apr-06 20:34

13-Apr-06 20:34

Deleting an object doesn't invalidate the pointer to the object.

You need to do:

delete object;
object=null;

I'm not sure how to check if deleting of the object actually worked...anyone...anyone..

- S
50 cups of coffee and you know it's on!

pjmvn13-Apr-06 20:49

13-Apr-06 20:49

Steve Echols wrote:
You need to do:

delete object;
object=null;

Thanks, but if i do this code. The program does bot call:
int j=object->value;
and the error does not occur. Smile | :)

Above is a simple example, my problem is very complicate and i can not set NULL to object.
Thanks again.

-- modified at 2:55 Friday 14th April, 2006

Steve Echols13-Apr-06 21:00

13-Apr-06 21:00

Maybe I'm misunderstanding your problem...

If you delete an object, you can no longer access that object.

I.e. if you do:

delete object;

You are not allowed to access any member of the object, since it is "gone" (i.e. object->value will return something you don't expect).

If you do:

delete object;
object=null;

And then try to access object->value, you will most likely get an access violation (which is correct).

This is correct:
[By correct, I mean the code works, but don't do it this way, since you know you just deleted the object.]

delete object;
object=null;

if (!object)
{
// the object is deleted, you can't access it
}
else
{
int j = object->value;
}

Does that make sense?

- S
50 cups of coffee and you know it's on!

-- modified at 3:06 Friday 14th April, 2006

pjmvn13-Apr-06 21:21

13-Apr-06 21:21

Steve Echols wrote:
This is correct:

delete object;
object=null;

if (!object)
{
// the object is deleted, you can't access it
}
else
{
int j = object->value;
}

Yes, if i do that my problem will be fixed.
But this code is a simple problem. my problem complicate than that, and i don't permission to set object = NULL; i just have permission to access it and check it for existing or deleted.
So if you know how to check it for existing(not deleted) please give me that code.
try{}catch("what is here"){} or other way?
Thanks again.

Steve Echols13-Apr-06 21:27

Re: Service/Socket/Threads/

13-Apr-06 21:27

From the code from your first post, you have permission to delete the object, but not set it to null? That's strange. I'd have to see some more code to see what's going on....

- S
50 cups of coffee and you know it's on!

Service/Socket/Threads/

syntaxed13-Apr-06 19:42

syntaxed

13-Apr-06 19:42

im developing a udp based client/service app that requires to be windows service apps.

serverService: a service that sends/recv the data to/from client.
i used WaitforSingleObject as a timer for serverService in a while(1) loop, that signals the event and serverService sends data to the clientService. the loop starts whenever the ServiceMain() is called from the SCM.

clientservice: a service that sends/recv data from server
similarly, i used WaitForSingleObject as a timer for my clientservice app, which sends the data to serverService very well.

but fortunately, both the services are unable to receive anything. even the OnReceive() Event is not getting triggered.

while i run the exact code using a Dialog-based app, both apps(client/server) runs fine and to the desired expectations.

Findings:
Therefore, just recognized after a fairly fine debugging that the neither serverService nor clientService was receiving any thing from each other, altho both services are sending the data.

it seems that, because both the services are in while loop therefore they can only do the tasks called from within the while loop.

Workaround:
so i guess i wud have to start another while(1) loop for both the services... that shud check and read the port for any prospective incoming message.

Results:
well, i did the above mentioned workaround, like while(1) ReceiveFrom(...), but once again, fortunately, it did not work.

Conclusion:
CAsyncSocket requires a message pump. Any ideas where shud i put my message_pump, the loop, so that i may get the exact message for the OnReceive to be called. Any snippets, links, articles?

Anybody has used the sockets in service??? Send() is S_OK, but How to Receive()??

Any ideas for the simple problem?

Best regards,
JT!

syntaxed13-Apr-06 23:20

syntaxed

13-Apr-06 23:20

Anyone?

Best regards,
JT!

Re: Service/Socket/Threads/

Robert M Greene14-Apr-06 9:21

Robert M Greene

14-Apr-06 9:21

Windows services don't have message loops or perform hidden windows (usually). I did create a service one time that had a peekmessage loop and a hidden window bag in the good old days.

The best alternative is to use a different socket class that doesn;t depend on theses items.
I seem to remember using
http://www.codeproject.com/internet/casyncsocketex.asp[^]

in a service once. Check it out and see if it works for you or not.

.............................
There's nothing like the sound of incoming rifle and mortar rounds to cure the blues. No matter how down you are, you take an active and immediate interest in life.

Fiat justitia, et ruat cælum

Lines

sataoa13-Apr-06 18:56

sataoa

13-Apr-06 18:56

Hello,
Using the MoveTo And LineTo function i can able to draw the line but now i want to draw the horizontal or vertical line then what should i do?

Laxman Auti13-Apr-06 19:01

Laxman Auti

13-Apr-06 19:01

Whenever you draw horizontal line change the x co-ordinate only and when user push left button down then save the y-coordinate and use it for drawing

same case for vertical lines change the y-co-ordinate and persist x co-ordinate

good luck

Knock out "T" from CAN'T
You 'CAN' if you think you 'CAN'
Cool | :cool:

sataoa13-Apr-06 19:42

sataoa

13-Apr-06 19:42

Thaks for this valuabe suggestion. Please tell me how give the dimesion to that peritcular entity such as line or rectagle.Hope for ur positive response toward me as am just started to learn MFC.

Steve Echols13-Apr-06 21:16

13-Apr-06 21:16

MoveTo updates the current position. LineTo will draw a line from the current position to the specified point, and update the current position to the new point

To draw a rectangle, I believe you can do:

MoveTo(0, 0); // initial position
LineTo(5, 0); // draw top
LineTo(5, 5); // draw right
LineTo(0, 5); // draw bottom
LineTo(0, 0); // draw left

Does that help?

- S
50 cups of coffee and you know it's on!