Re: delete pointer. - C / C++ / MFC Discussion Boards

Re: delete pointer.

Cedric Moonen13-Jun-06 22:10

Cedric Moonen

13-Jun-06 22:10

That's a very clear description of the problem Unsure | :~

The solution is: you did something wrong.

Cédric Moonen
Software developer

Charting control

Re: delete pointer.

see me13-Jun-06 22:21

see me

13-Jun-06 22:21

Thats a very precious information for me.
Thank you..

yours faithfully
ajeeshcv

Re: delete pointer.

Cedric Moonen13-Jun-06 21:54

Cedric Moonen

13-Jun-06 21:54

What is the exact error ?

Maybe your pointer points to an invalid address. You probably left it uninitialized and then try to delete it.

Cédric Moonen
Software developer

Charting control

Re: dlete pointer. [modified]

Viorel.13-Jun-06 21:48

Viorel.

13-Jun-06 21:48

Possible causes:

un-initialized pointer, like int * p; delete p;
pointer does not point to an object created with new: int x; int * p = &x; delete p;
multiple execution of delete: int * p = new int; delete p; delete p;
pointed zone was altered by other code: int * p = new int; memset(p-100, 0, 1000); delete p;

int * p = NULL; delete p;

Re: delete pointer.

see me13-Jun-06 22:05

see me

13-Jun-06 22:05

In my case the above mentioned 4 cases will not be satisfied.
Actual reason is any other.:->

And also as per ur comments
int * p = NULL; delete p;

how the datas will be deleted from the location which is pointed by p initialy.
since u r saying to delete the pointer after asigning the pointer to null. Confused | :confused:

yours faithfully
ajeeshcv

Re: delete pointer.

toxcct13-Jun-06 22:12

toxcct

13-Jun-06 22:12

Ajeesh c v wrote:
int * p = NULL; delete p;

how the datas will be deleted from the location which is pointed by p initialy.
since u r saying to delete the pointer after asigning the pointer to null.

he doesn't say it is the things to do...

the cases enumerated are possible causes for a crash when deleting a pointer Dead | X|

TOXCCT >>> GEII power

[VisualCalc 3.0 updated ][Flags Beginner's Guide new! ]

Re: delete pointer.

Cedric Moonen13-Jun-06 22:13

Cedric Moonen

13-Jun-06 22:13

Ajeesh c v wrote:
how the datas will be deleted from the location which is pointed by p initialy.
since u r saying to delete the pointer after asigning the pointer to null.

That's probably your problem. When you do this:

int* pTest;
if (pTest)
   delete pTest;

You will have an excpetion because you try to delete memory that is unitianalized (you can only delete memory that has been allocated with new). So, to be sure not to delete this 'unexistant' memory, assign NULL to the pointer. This is safe.

Cédric Moonen
Software developer

Charting control

Re: delete pointer.

Viorel.13-Jun-06 22:16

Viorel.

13-Jun-06 22:16

According to documentation (http://msdn2.microsoft.com/en-us/library/h6227113.aspx[^]), “You can [...] use delete on a pointer with the value 0”.

Therefore instead of

if( p != NULL )
{
    delete p;
    p = NULL;
}

you can use

delete p;
p = NULL;

However, this does not belong to original topic. I think you should put a breakpoint at the line where your block of memory is allocated and the pointer is assigned. Then investigate the pointer’s value and the content of the memory block. Then stop on the line where the pointer is deleted. Check if the pointer contains right address value. Try to use step-be-step execution during deletion. Perhaps the pointer points to an object having destructor, and the problem is within this function.

Re: dlete pointer.

John R. Shaw13-Jun-06 21:50

John R. Shaw

13-Jun-06 21:50

You need to be more specific, what do you mean by delete a pointer? I assume memory pointer, but these days it is hard to say. What compiler of language are you using?

INTP
"Program testing can be used to show the presence of bugs, but never to show their absence."Edsger Dijkstra

Re: dlete pointer.

Hamid_RT13-Jun-06 22:10

Hamid_RT

13-Jun-06 22:10

Can you show how to use pointer and how to declare pointer

whitesky

Re: delete pointer.

see me13-Jun-06 22:27

see me

13-Jun-06 22:27

The pointer is of a dialog.

Initialization:
CMyDialog* pMyDialog;
pMyDialog = new CMyDialog;

pMyDialog->EndDialog(0);

if(pMyDialog)
{
delete pMyDialog;
pMyDialog = 0;
}

yours faithfully
ajeeshcv

Re: delete pointer.

Hamid_RT13-Jun-06 22:51

Hamid_RT

13-Jun-06 22:51

im not sure your problem is this but
how to create dialog? and if you run your code i think you get a error in pMyDialog->EndDialog(0);
now try this and send me if you have a error

<br />
CMyDialog* pMyDialog;<br />
pMyDialog = new CMyDialog;<br />
pMyDialog->Create(IDD_TEST);//id from dialog<br />
pMyDialog->EndDialog(0);<br />
delete pMyDialog ;<br />
pMyDialog = 0;<br />

whitesky

how to know the values for event masks

thathvamsi13-Jun-06 21:12

thathvamsi

13-Jun-06 21:12

Hey ...
I am new inthis area. I am interested in knowing the values for the event masks used in GetCommMask and SetCommMask functions. ie., EV_BREAK = 0x????
How do i know which event is activated or received?
Any help/guide??

Re: how to know the values for event masks

Viorel.13-Jun-06 21:19

Viorel.

13-Jun-06 21:19

You can see these values in WinBase.h file, which is in a subfolder of Visual Studio.

Re: how to know the values for event masks

thathvamsi13-Jun-06 22:37

thathvamsi

13-Jun-06 22:37

hey... thanks for that. this winbase.h file explains lot of my other doubts.

Re: how to know the values for event masks

Hamid_RT13-Jun-06 22:20

Hamid_RT

13-Jun-06 22:20

See Here[^] maybe it is some helpful to you

whitesky

Re: how to know the values for event masks

thathvamsi13-Jun-06 22:36

thathvamsi

13-Jun-06 22:36

Thanks very much for the link. it s very helpful.

Open vc8 project using vc7.1 [modified]

chybin13-Jun-06 20:55

chybin

13-Jun-06 20:55

How to open vc8 project using vc7.1?

-- modified at 2:55 Wednesday 14th June, 2006

Error when using libavcodec dll in vc++

RahulOP13-Jun-06 20:50

RahulOP

13-Jun-06 20:50

Hi,

In continuance with my earlier posts,I can now link this dll and am also able to call some of its functions without any problems.

AVCodecContext *avctx;<br />
AVCodec *codec;<br />
avctx = new AVCodecContext;<br />
codec = new AVCodec;<br />
HMODULE hDll = LoadLibrary("avcodec.dll");<br />
if(hDll== NULL)<br />
{<br />
CString str;<br />
int a = GetLastError();<br />
str.Format("%d",a);<br />
AfxMessageBox(str);<br />
AfxMessageBox("first");<br />
AfxMessageBox("Failed loading1");<br />
}<br />
<br />
typedef void (avcodec_init)();<br />
avcodec_init* p = (avcodec_init*)GetProcAddress(hDll, "avcodec_init");<br />
if(p==NULL)<br />
AfxMessageBox("Failed loading2");<br />
p();<br />
//FreeLibrary(hDll);<br />
<br />
HMODULE hDll1a = LoadLibrary("avcodec.dll");<br />
typedef void (avcodec_register_all)();<br />
avcodec_register_all* p1a = (avcodec_register_all*)GetProcAddress(hDll1a, "avcodec_register_all");<br />
if(p1a==NULL)<br />
AfxMessageBox("Failed loading3");<br />
p1a();<br />
if(p1a==NULL)<br />
AfxMessageBox("Failed loading1.1");<br />
<br />
<br />
HMODULE hDll3 = LoadLibrary("avcodec.dll");<br />
typedef void (avcodec_find_encoder)(int CODECID);<br />
avcodec_find_encoder* p3 = (avcodec_find_encoder*)GetProcAddress(hDll3, "avcodec_find_encoder");<br />
if(p3==NULL)<br />
AfxMessageBox("Failed loading3");<br />
p3(CODEC_ID_MP2);<br />
if(p3==NULL)<br />
AfxMessageBox("Failed loading3");<br />
<br />
<br />
codec=(AVCodec *)p3;<br />
<br />
HMODULE hDll4 = LoadLibrary("avcodec.dll");<br />
//(hDll should not be NULL here)<br />
typedef void (avcodec_alloc_context)();<br />
avcodec_alloc_context* p4 = (avcodec_alloc_context*)GetProcAddress(hDll4, "avcodec_alloc_context");<br />
if(p4==NULL)<br />
AfxMessageBox("Failed loading4");<br />
p4();<br />
if(p4==NULL)<br />
AfxMessageBox("Failed loading4");<br />
<br />
<br />
avctx=(AVCodecContext *)p4;<br />
if(avctx==NULL){<br />
CString str;<br />
int a = GetLastError();<br />
str.Format("%d",a);<br />
AfxMessageBox(str);}<br />
avctx->bit_rate=64000;<br />

The last line throws the error and AfxMessageBox simply displays the number 2. The HELP section has no entry for 2.
Somebody please help!!

Re: Error when using libavcodec dll in vc++

Cedric Moonen13-Jun-06 20:59

Cedric Moonen

13-Jun-06 20:59

First thing, it is unnecessary to call LoadLibrary multiple times. Once you get the handle, you can load as many functions as you want with the same handle. So remove the redundant LoadLibrary.

RahulOP wrote:
avctx=(AVCodecContext *)p4;
if(avctx==NULL){
CString str;
int a = GetLastError();
str.Format("%d",a);
AfxMessageBox(str);}
avctx->bit_rate=64000;

And what are you trying to do here ? You are casting a function pointer into a pointer of type AVCodecContext*. That's logical that you will have some problems. You try to get a return from the function ? Then you need to put the exact function prototype in the typedef (with the return and the arguments of the function). Then, you can simply call it like another function and get the returned value.

Cédric Moonen
Software developer

Charting control

Re: Error when using libavcodec dll in vc++

RahulOP13-Jun-06 21:09

RahulOP

13-Jun-06 21:09

Cedric Moonen wrote:
And what are you trying to do here ? You are casting a function pointer into a pointer of type AVCodecContext*. That's logical that you will have some problems. You try to get a return from the function ? Then you need to put the exact function prototype in the typedef (with the return and the arguments of the function). Then, you can simply call it like another function and get the returned value.

AVCodecContext is defined in avcodec.h as struct.

I am sorry but I havent understood what you've written. Its gone so over my head, if I were to look up, it'd be a tiny speck Frown | :-(

Re: Error when using libavcodec dll in vc++

Cedric Moonen13-Jun-06 21:24

Cedric Moonen

13-Jun-06 21:24

RahulOP wrote:
AVCodecContext is defined in avcodec.h as struct.

Yes, basically, what you have is a pointer to a function (p4) and you try to cast this pointer to a structure AVCodecContext. Which is of course totally impossible. Why are you trying to do such a thing ? I guess it is because the function you get from the dll must return a strcture of this type, right ?

So, what you need to do, is declaring your prototype this way. Instead of:

typedef void (avcodec_alloc_context)();

write:

typedef AVCodecContext* (avcodec_alloc_context)();

Then, once you get the function from your dll (p4), simply call the function like you would do for a standard function:

AVCodecContext *avctx = p4();

The function will be called and it will return your pointer.

I guess you want to do that but I'm not sure. Could you confirm this please ?

Important: your typedefs must match exactly the prototype of the function inside your dll !! So, if your func returns an int, the typedef needs to return an int also.

BTW, where is this dll coming from ? Don't you have a header file and a lib file supplied with it ? This will be much easier for you.

Another thing: I see that on the top of the code snippet, you create a new VCodecContext structure (using new) but later, you assign a new value to this pointer. So, the memory is never released and you get a memory leak.

Cédric Moonen
Software developer

Charting control

Re: Error when using libavcodec dll in vc++

RahulOP13-Jun-06 21:41

RahulOP

13-Jun-06 21:41

I am using FFMPEG. Rather I built FFMPEG using MSYS and am using the dlls I got from there. Yes I got the lib files as well and trying to do the same avocdec_init(); directly gave me a lot of linker errors LNK 2019 and LNK2001.

You can see the avcodec.h file here
http://svn.mplayerhq.hu/ffmpeg/trunk/libavcodec/

There's also an apiexample.c which is what I am trying to work off from.

I was under the impression that I am supposed to use the new when I initialise.
Thank you for your help so far Smile | :)

Re: Error when using libavcodec dll in vc++

Cedric Moonen13-Jun-06 21:50

Cedric Moonen

13-Jun-06 21:50

You didn't answer my question: are you trying to do what I asked ? So, you have a function that returns a strcture (or a pointer to the struct) and you want to get it ? What is the exact prototype of the function "avcodec_alloc_context" ?

RahulOP wrote:
gave me a lot of linker errors LNK 2019 and LNK2001

Did you link properly to the lib file ? So, did you add the lib in the project settings ? Instead of taking a complicated way, why don't you simply try to correct the initial errors ?

If this dll is supplied with a lib file and a header file, then you can simply implicitely load the dll (not using LoadLibrary and GetProcAddress, but simply add the header file to your project and link to the library), this is much more easier to manage.

Cédric Moonen
Software developer

Charting control

Re: Error when using libavcodec dll in vc++

Eytukan13-Jun-06 22:11

Eytukan

13-Jun-06 22:11

I think he's shooting in the dark!

<marquee scrollamount="1" scrolldelay="1" direction="up" height="10" step="1">--[ Jig | [Dance]

]--

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