Re: How to check null or corrupted char pointer value - C / C++ / MFC Discussion Boards

How to check null or corrupted char pointer value

KASR18-Jan-09 0:11

8-Jan-09 0:11

const char *pVar;
we can check (pVar == NULL) for null values.
How to check when the pVar contains bad pointer(not NULL)?

Re: How to check null or corrupted char pointer value

Abhijit A8-Jan-09 0:34

Abhijit A

8-Jan-09 0:34

to check bad ponter for string use

use BOOL IsBadStringPtr(LPCTSTR lpString,WORD uuMaxLen)

for example:
const char *pVar;

if(IsBadStringPtr((LPCTSTR)pVAr,1)==TRUE)
//pVar contains bad pointer or memory is not allocated to pVar
else
//pVar contains memory allocated with it

abhi

Re: How to check null or corrupted char pointer value [modified]

CPallini8-Jan-09 0:38

CPallini

8-Jan-09 0:38

Simply put: you cannot. That's the reason to set pVar=NULL ~~just before~~ immediately after freeing its associated memory.
However it depends on your definition of 'bad pointer' (IMHO a variable wrongly pointing a valid memory area is also 'bad'...).
Smile | :)

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]

modified on Thursday, January 8, 2009 6:48 AM

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 0:47

KASR1

8-Jan-09 0:47

Actually the pVar is assigned NULL and passed to a DLL.
The DLL assigned pVar to bad pointer.

Re: How to check null or corrupted char pointer value

Cedric Moonen8-Jan-09 0:50

Cedric Moonen

8-Jan-09 0:50

KASR1 wrote:
Actually the pVar is assigned NULL and passed to a DLL.
The DLL assigned pVar to bad pointer.

Can you post the code of what the dll is doing ?

Cédric Moonen
Software developer

Charting control [v1.5]
OpenGL game tutorial in C++

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:02

KASR1

8-Jan-09 1:02

please see reply to pallini.

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:27

KASR1

8-Jan-09 1:27

Prototype:
typedef HRESULT (STDAPICALLTYPE * LPFPTRANSLATE) (char* psz1, char* &psz2);

second parameter i am getting bad pointer.

Re: How to check null or corrupted char pointer value

CPallini8-Jan-09 0:52

CPallini

8-Jan-09 0:52

I fixed my (obviuosly Blush | :O

) wrong reply.
What is pVar expected to be by the DLL (i.e. what is the prototype of the DLL's function)?

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 0:58

KASR1

8-Jan-09 0:58

Its a third party DLL.(we don't have code)

Prototype:
typedef HRESULT (STDAPICALLTYPE * LPFPTRANSLATE) (char* psz1, char* &psz2);

second parameter i am getting bad pointer.

Re: How to check null or corrupted char pointer value

toxcct8-Jan-09 1:06

toxcct

8-Jan-09 1:06

How do you know it is a "bad" pointer ?

[VisualCalc][Binary Guide][CommDialogs] | [Forums Guidelines]

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:14

KASR1

8-Jan-09 1:14

Program crashes when accessing value from second parameter passed ie., psz2

Re: How to check null or corrupted char pointer value

toxcct8-Jan-09 1:16

toxcct

8-Jan-09 1:16

KASR1 wrote:
Program crashes when accessing value from second parameter passed

...with a particuliar error message by any chance ?

[VisualCalc][Binary Guide][CommDialogs] | [Forums Guidelines]

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:25

KASR1

8-Jan-09 1:25

Throws 'access denied' error message.

Re: How to check null or corrupted char pointer value

Randor 8-Jan-09 1:34

Randor

8-Jan-09 1:34

The segfault pretty much tells you that its a bad pointer. If you want to have a look at the properties of the memory address being passed you can do something like:

MEMORY_BASIC_INFORMATION mbi;
VirtualQueryEx(GetCurrentProcess(),pVar,&mbi,sizeof(mbi));

The member mbi.Protect will be probably be PAGE_NOACCESS. But of course you already have this knowledge.

Best Wishes,
-David Delaune

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:59

KASR1

8-Jan-09 1:59

Yes it works fine.
Thanks a lot.

Re: How to check null or corrupted char pointer value

CPallini8-Jan-09 1:34

CPallini

8-Jan-09 1:34

Are you calling it this way (assuming 'translate' as the name of the function pointer)?

char * psz1 = "Hello";
char * psz2;
HRESULT hr = translate( psz1, psz2);

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:41

KASR1

8-Jan-09 1:41

yes. small change as below

char * psz1 = "Hello";
char * psz2 = NULL;
HRESULT hr = translate( psz1, psz2);

Re: How to check null or corrupted char pointer value

CPallini8-Jan-09 1:50

CPallini

8-Jan-09 1:50

Well, psz2 initialization shouldn't matter.
Have you any documentation of the library?
(Maybe the function has some weird pre-requisite, like psz2 pointing to a client-allocated buffer...I know it doesn't make sense, but several real pieces of code actually does not make sense).

Smile | :)

Re: How to check null or corrupted char pointer value

KASR18-Jan-09 1:57

KASR1

8-Jan-09 1:57

Thanks for replying soon.

The below logic given by Randor seems working.

MEMORY_BASIC_INFORMATION mbi;
VirtualQueryEx(GetCurrentProcess(),pVar,&mbi,sizeof(mbi));
if (mbi.Protect == PAGE_NOACCESS)
{
   // bad pointer
}

Re: How to check null or corrupted char pointer value

CPallini8-Jan-09 2:06

CPallini

8-Jan-09 2:06

I'm glad about, but doesn't the HRESULT return value give some info about the translate operation?

Re: How to check null or corrupted char pointer value

Randor 8-Jan-09 2:19

Randor

8-Jan-09 2:19

Well, technically it could be other values. For example you may recieve a ramdom garbage pointer which resolves to a loaded PE image. A better implementation for checking a variable pointer would be:

MEMORY_BASIC_INFORMATION mbi;
VirtualQueryEx(GetCurrentProcess(),pVar,&mbi,sizeof(mbi));
if (mbi.Protect == PAGE_READWRITE && mbi.State = MEM_COMMIT && mbi.Type == MEM_PRIVATE)
{
	// bad string pointer
}

This ensures:

1.) You can read and write to the address.
2.) The address is allocated and committed memory.
3.) The address is within the private region.

At this point the chance of being a good pointer has become substantially higher.

Best Wishes,
-David Delaune

INetFwMgr

barneyb817-Jan-09 23:11

barneyb81

7-Jan-09 23:11

I'm trying to obtain the Windows Firewall status, which is simple enough using the get_FirewallEnabled method on INetFwProfile. The problem is that this only retrieves the local policy, which could have been overridden by the group policy and so is sometimes wrong.

Does anyone know if there's a way of retrieving the group policy? There's a get_CurrentProfileType on INetFwMgr, but this just seems to return NET_FW_PROFILE_STANDARD regardless of the policy. There's a NEW_FW_POLICY_TYPE enum, but it's not used in any methods that I can find.

Thanks!

Re: INetFwMgr

Hamid_RT7-Jan-09 23:48

Hamid_RT

7-Jan-09 23:48

MSDN has examples for work with Firewall did you see
Using Windows Firewall API[^]?

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: INetFwMgr

barneyb817-Jan-09 23:55

barneyb81

7-Jan-09 23:55

Thanks. I'd read through this documentation, and can't find any way of obtaining the group policy (or indeed even of telling whether or not the local policy is being overridden). Given the existence of the NET_FW_POLICY_TYPE enum, I'd like to think it's possible, but I'm starting to think maybe it's not...

protocol using vc++

hrishiS7-Jan-09 22:09

hrishiS

7-Jan-09 22:09

hello Experts,
I would like to know the basics of how to use SIP protocol using vc++.This is not regards to any project. Just for my self learning.

Thanks,
Himangshu

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.