C / C++ / MFC Discussion Boards

Re: How to verify a pointer is valid? [modified]

Stephen Hewitt13-Jun-06 18:09

13-Jun-06 18:09

Using IsBadWritePtr and friends will not solve the OP's problem. IsBadWritePtr can return FALSE even after an object as been deleted as heap blocks can be marked as free but the memory still be allocated. On top of this the CRT can add another level of caching. In short, if IsBadWritePtr returns TRUE you know something is wrong and it's not safe to use the memory, but if returns FALSE it does not necessarily mean all is well.

Steve

Re: How to verify a pointer is valid? [modified]

Nibu babu thomas13-Jun-06 17:55

Nibu babu thomas

13-Jun-06 17:55

flyingxu wrote:
But now I want to use the pointer of pSave, can I verify if pSave is valid or not before I use it?
try/catch?
or any method else?

Look up _set_new_handler, _set_new_mode, _query_new_handler, AfxSetNewHandler (this is not documented).

The above functions transfers control to your error-handling mechanism if the new operator fails to allocate memory.

These functions (except for _set_new_mode and _query_new_handler) take a function pointer as an argument and returns the old one. The _query_new_handler function returns the address of the current new handler.

Make sure you set the old one back before exiting.

PNH old_handler = _set_new_handler( my_handler );
// Code that requires my_handler
_set_new_handler( old_handler )
// Code that requires old_handler

Nibu thomas
A Developer

Programming tips[^] My site[^]

Re: How to verify a pointer is valid?

grigsoft13-Jun-06 18:09

grigsoft

13-Jun-06 18:09

Of course, it is offtopic, but I would say that requirement to verify if pointer is good or not is a result of bad objects intraction design. There never should be invalid pointers, because you will forget to verify it once - either now or when you will have to modify your code one year later.

Igor Green
http://www.grigsoft.com/ - files and folders comparison tools

Re: How to verify a pointer is valid?

Ganesh_T13-Jun-06 18:37

Ganesh_T

13-Jun-06 18:37

Check this link[^]

Cheers
"Peace of mind through Technology"

Re: How to verify a pointer is valid?

Laxman Auti13-Jun-06 18:49

Laxman Auti

13-Jun-06 18:49

flyingxu wrote:
But now I want to use the pointer of pSave, can I verify if pSave is valid or not before I use it?
try/catch?

Use ASSERT in Debug mode B'coz it works in Debug mode only.

Knock out 't' from can't,
You can if you think you can
Cool | :cool:

Re: How to verify a pointer is valid?

Tim Paaschen13-Jun-06 19:35

Tim Paaschen

13-Jun-06 19:35

You may use a smart pointer that implements reference counting, e.g. boost::shared_ptr<csomeobject>, instead of raw pointer.

graphical error

anmol m13-Jun-06 17:12

anmol m

13-Jun-06 17:12

hi there can anyone out there help me with "egavga.bgi" error

Adi

Re: graphical error

Ganesh_T13-Jun-06 18:40

Ganesh_T

13-Jun-06 18:40

egavga.bgi is an Device driver file...
I think this is missing .

You have to download it and place it in valid location

Cheers
"Peace of mind through Technology"

Re: graphical error

Laxman Auti13-Jun-06 18:45

Laxman Auti

13-Jun-06 18:45

anmol m wrote:
hi there can anyone out there help me with "egavga.bgi" error

This error mostly seen in Turbo C++ Editers while doing graphics related work.
Set the BGI library path properly to work.

Knock out 't' from can't,
You can if you think you can
Cool | :cool:

Re: graphical error

khan++13-Jun-06 18:46

khan++

13-Jun-06 18:46

Exactly what error is being reported?
At runtime, your DOS program using the BGI needs this graphics driver file, unless you have embedded it into the executable.
More details are needed to correctly interpret the error.

this is this.

Re: graphical error

anmol m15-Jun-06 7:11

anmol m

15-Jun-06 7:11

thanks mate, i was compi. a matrix calculator and on running error comes saying that graphics not initiliased use initgraph.
pl. if you have a prog which i can give for my board exami.pl mail it code to me
once again tanks
anmol m

f*** fear drink beer

Re: graphical error

khan++15-Jun-06 21:12

khan++

15-Jun-06 21:12

I do not have the Turbo C compiler here at the moment.
You will find lots of examples even with the Turbo C IDE. Go into the examples directory, and there is a lot of help.
Here is an example. You can search in google for initgraph:
http://www.cs.colorado.edu/~main/cs1300/doc/bgi/initgraph.html[^]

Just make sure that you copy the file egavga.bgi to the folder where you are working. Also there is a setting in the IDE which chooses if graphics are to be allowed or not (I do not remember it right now). Look somewhere in the options.

this is this.

A newb needs help.

zach713-Jun-06 16:01

zach7

13-Jun-06 16:01

I really need help. I dont know the first thing about C++ and C++ is such a huge language. Im so lost. Where should I start. I went to the beginners section of C++ tutorials and I looked at the bits and bytes tutorial and it was really confusing.

Re: A newb needs help.

Mark F.13-Jun-06 17:15

Mark F.

13-Jun-06 17:15

Most of the beginner stuff here assumes that you have a reasonable grasp of programming basics already. Once you understand the concepts moving from one language to another is more or less syntax. IMO Smile | :)

I suggest that you go to the local library, local book store, and online and do a little reading on the basic fundamentals of C++. You will also need an editor/compiler IDE (Integrated Development Environment) software program in order to write, compile, and your run programs.

I live in a college town and was able to get second-hand programming books from local stores cheap. I even bought my first copy of MS Visual Studio (Learning Edition) there too.

Here are some online resources to get you started:
http://cplus.about.com/od/beginnerctutorial/[^]
http://devcentral.iftech.com/articles/C++/default.php[^]
http://msdn.microsoft.com/visualc/[^]
http://www.freeprogrammingresources.com/cppbooks.html[^]

And of course at this site.

Mark Wink | ;)

Re: A newb needs help.

Ganesh_T13-Jun-06 18:46

Ganesh_T

13-Jun-06 18:46

REad th books such as:

Robert Lafore....is good one and can be easily available in the local book store.

Or Search for the tutorials google..
http://codersource.net/codersource_cppprogramming.html

Cheers
"Peace of mind through Technology"

Re: A newb needs help.

Laxman Auti13-Jun-06 18:53

Laxman Auti

13-Jun-06 18:53

zach7 wrote:
I really need help. I dont know the first thing about C++ and C++ is such a huge language. Im so lost. Where should I start. I went to the beginners section of C++ tutorials and I looked at the bits and bytes tutorial and it was really confusing.

http://www.cplusplus.com/doc/tutorial/[^]
Here is the good atritcals on C++

Knock out 't' from can't,
You can if you think you can
Cool | :cool:

popup menu in a listbox [modified]

locoone13-Jun-06 15:48

locoone

13-Jun-06 15:48

how do i show the menu in a listbox i have the menu resource i want to use a right click to show the menu i have the right click function but i dont know how to call the menu.
im using MFC/Visual C++ 6.0

and i have this bit of code
enum FindOptionsEnum
{
FIND_SIZE = (1L << 0),
FIND_DATEMODIFIED = (1L << 1),
FIND_DATECREATED = (1L << 2),
FIND_DATEACCESSED = (1L << 3),
FIND_ATTRIBUTES = (1L << 4),
FIND_TEXT = (1L << 5),
};
but when i try to #include "vfw.h"
the compiler gives a error on that code anyone know why?

error C2059: syntax error : 'constant'
error C2143: syntax error : missing ';' before '}'
error C2143: syntax error : missing ';' before '}'
all 3 errors goto that code
-- modified at 21:55 Tuesday 13th June, 2006

Re: popup menu in a listbox

Sarath C13-Jun-06 17:38

Sarath C

13-Jun-06 17:38

map the right click message of the control
and use a CMenu object to create popup menu

MSDN has the sample code

here it is

// The code fragment below shows how to create a new menu for the
// application window using CreateMenu() and CreatePopupMenu().
// Then, the created menu will replace the current menu of the
// application. The old menu will be destroyed with DestroyMenu().
// NOTE: The code fragment below is done in a CFrameWnd-derived class.

// Create a new menu for the application window.
VERIFY(m_NewMenu.CreateMenu());

// Create a "File" popup menu and insert this popup menu to the
// new menu of the application window. The "File" menu has only
// one menu item, i.e. "Exit".
VERIFY(m_FileMenu.CreatePopupMenu());
m_FileMenu.AppendMenu(MF_STRING, ID_APP_EXIT, (LPCTSTR)"E&xit");
m_NewMenu.AppendMenu(MF_POPUP, (UINT) m_FileMenu.m_hMenu, "&File");

// Remove and destroy old menu
SetMenu(NULL);
CMenu* old_menu = CMenu::FromHandle(m_hMenuDefault);
old_menu->DestroyMenu();

// Add new menu.
SetMenu(&m_NewMenu);

// Assign default menu
m_hMenuDefault = m_NewMenu.m_hMenu;

Sa^Rath.

"Don't Do Different things... Do Things Differently..."

Understanding State Pattern in C++

Re: popup menu in a listbox

Hamid_RT13-Jun-06 19:41

Hamid_RT

13-Jun-06 19:41

if you need to right click for menu do you see WM_CONTEXTMENU

whitesky

Re: popup menu in a listbox

Hamid_RT13-Jun-06 20:09

Hamid_RT

13-Jun-06 20:09

did you saw vfw.h you use from FIND_SIZE and ... that are in these file

whitesky

Re: popup menu in a listbox

Hamid_RT14-Jun-06 19:12

Hamid_RT

14-Jun-06 19:12

if you want to show menu only in listbox use from a if
if(pWnd->m_hWnd==m_List.m_hWnd) then menu functions

whitesky

Find a certain text string on the IE's current loaded webpage

Joseph Lee13-Jun-06 15:13

Joseph Lee

13-Jun-06 15:13

Hi,
I wanna make a simple application that finds a certain text string periodically on the Internet Explorer's current loaded webpage. If it finds text that I predefined, it will pop-up message box and that's all.
This webpage is updated quite often by server without user's input.

Could you suggest any briliant idea to make this simple & fast? Wink | ;)

Re: Find a certain text string on the IE's current loaded webpage

Ganesh_T13-Jun-06 18:55

Ganesh_T

13-Jun-06 18:55

PLease see the IHtmlDocument2 interface in the MSDN you can find all the methods which are exposed by this interface.

Cheers
"Peace of mind through Technology"

Re: Find a certain text string on the IE's current loaded webpage

Laxman Auti13-Jun-06 18:55

Laxman Auti

13-Jun-06 18:55

Joseph Lee wrote:
Could you suggest any briliant idea to make this simple & fast?

You may required to write plugin for IE which keep track of webpages.

Knock out 't' from can't,
You can if you think you can
Cool | :cool:

openGL,memory leak with glDrawPixels

leon913-Jun-06 14:16

leon9

13-Jun-06 14:16

Hello everyone,

Im displaying a captured image onto the the screen. I use the following code to display the image.

<br />
void draw()<br />
{<br />
   if(m_imageData == NULL)<br />
	return;<br />
   glPixelStorei(GL_UNPACK_ALIGNMENT,1);<br />
   glRasterPos2i(m_xOffset,m_yOffset);<br />
   glDrawPixels(m_width,m_height,GL_RGBA,GL_UNSIGNED_BYTE,m_imageData);<br />
   glFlush();<br />
}<br />

the fuction draws the image ok but the glDrawPixels function creates a memory leak. Does anyone know a work around glDrawPixels or a way to track the memory leak (don't know if it's possible on my end since it's a openGL function).

Thank's everyone

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