C / C++ / MFC Discussion Boards

BadKarma31-May-06 0:05

31-May-06 0:05

The pointer points to an address on the stack (local declared variable)
this address still exist after the function returns. When you immediatly
use the pointer to get its value there is no problem.
But if there are serveral function calls happend in between or a large object
is created on stack the data at the specific address will be lost. When
your stack size is decreased you could also get an access violation.

codito ergo sum

Re: Why this is not failing in VC6

Sarath C30-May-06 23:57

Sarath C

30-May-06 23:57

U will get some consideration in a debug build that is the allocated space and pointer accessing etc. it wont fail in some cases ( but it should fail in such scenarios).

Just try the same code in release build. it wont definitely behave like debug build.

In release build too the application error is not occuring because the mapped address in its process address space.

Sa^Rath

"D on't blindly follow rules you read somewhere without verifying that it makes sense for your situation!"

Re: Why this is not failing in VC6

NiceNaidu31-May-06 0:01

NiceNaidu

31-May-06 0:01

SaRath C wrote:
In release build too the application error is not occuring because the mapped address in its process address space

yes..u r absolutely right. It is giving some other value in release build.

Now i understood the reason.

Thanks buddies.

Appu..
"If you judge people, you have no time to love them."

Re: Why this is not failing in VC6

Sarath C31-May-06 0:02

Sarath C

31-May-06 0:02

After this statement

NiceNaiduprintf("Value of *pPointer: %d\n", *pPointer);

do this

BOOL b = IsBadReadPtr(pPointer,sizeof(int));

check the value of b... it will be false because of the invalid pointer.

Sa^Rath

"D on't blindly follow rules you read somewhere without verifying that it makes sense for your situation!"

Re: Why this is not failing in VC6

Michael Dunn31-May-06 2:06

Michael Dunn

31-May-06 2:06

The local variable nNumber is allocated on the thread's stack. When SomeFunction() returns, its stack variables are not erased (or "deleted"), the stack pointer is just moved back to a higher address. The stack data will still be there in memory until some later code reuses that area of memory for its stack.

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

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Why "new" operator is "thread_safe" ?

Ajax9530-May-06 23:17

Ajax95

30-May-06 23:17

I'm currently reading some articals about Singleton.
It mentioned the following data structure is for single thread only
Class Singleton
{
public:
static Singleton * GetInstance()
{
static Singleton instance;
return &instance;
}
protected:
Singleton();
~Singleton();
}
Instead of using local static variable; using new operator to create an object will be thread-safe.
Class Singleton
{
private:
Singleton * m_pInstance;
public:
static Singleton * GetInstance()
{
if (! m_pInstance)
m_pInstance = new Singleton();
return m_pInstance;
}
protected:
Singleton();
~Singleton();
}

I can't see the real difference between these two implementation. Why the one with new operator is thread-safe?

Thanks

Re: Why "new" operator is "thread_safe" ?

BadKarma30-May-06 23:40

BadKarma

30-May-06 23:40

you are correct, the second sample is NOT threadsafe. Its worse there can also be a memory leak

You should protect the creation with a critical section.
But beware, it is not because the creation of your singleton is threadsafe that the data the singleton wraps will be threadsafe.

codito ergo sum

Re: Why "new" operator is "thread_safe" ?

Nemanja Trifunovic31-May-06 1:28

Nemanja Trifunovic

31-May-06 1:28

None of them are thread-safe, and actually chances are you would experience a threading problem with the second version sooner than with the first one.

My programming blahblahblah blog. If you ever find anything useful here, please let me know to remove it.

C++ and ADO problem

antonaras30-May-06 22:58

antonaras

30-May-06 22:58

Hi again

I hava a problem again executing an sql statment(INSERT) in my program
can anyone help me find whats wrong?

hr = S_OK;<br />
	CoInitialize(NULL);<br />
<br />
	try<br />
	{<br />
		_ConnectionPtr m_pConn;<br />
		HRESULT hr =m_pConn.CreateInstance(__uuidof(Connection));<br />
		if (FAILED( hr ))<br />
			cout<<"Can't create an intance of ADO.Connection"<<endl;<br />
 <br />
		if (FAILED( m_pConn->Open(_bstr_t("Provider=Microsoft.Jet.OLEDB.4.0;Data Source =ADOTestDB.MDB"),<br />
			_bstr_t( "" ),<br />
			_bstr_t( "" ), <br />
			adModeUnknown )))<br />
			<br />
			cout<<"Can't open datasource"<<endl;<br />
<br />
<br />
<br />
<br />
		_bstr_t strDepId="12";<br />
		_bstr_t strName="Art";<br />
		_bstr_t strOfficeNo="256";<br />
		_bstr_t strTel="22491303";<br />
		_bstr_t strDepHead="Dr.Antonis Marcou";<br />
<br />
		_bstr_t strSQL("Insert into Dept(DeptID,Name,OfficeNo,Phone,DeptHead) Values(");<br />
		strSQL += strDepId + strName + strOfficeNo + strTel + strDepHead ;<br />
<br />
		printf("%s\n",(LPCSTR)strSQL);//The program works up to here then   it gives me an error:0x<br />
	<br />
		m_pConn->Execute(strSQL,NULL,adExecuteNoRecords);<br />
<br />
		printf("Data Added Successfully\n",(LPCSTR)strSQL);<br />
<br />
		m_pConn->Close();<br />
		<br />
	}catch( _com_error &ce )<br />
	{<br />
		printf("Error:%s\n",ce.Description);<br />
<br />
	}<br />
<br />
	CoUninitialize();

I wrote the program almost the same way as the sample code but still is not working

the fiels in the db are
DeptID: number
Name: Text
OfficeNo: number
Phone: text
DeptHead: text

Any ideas?
thanks a lot for all the help you gave me so far

Re: C++ and ADO problem

NiceNaidu30-May-06 23:05

NiceNaidu

30-May-06 23:05

I Think, u r going wrong in framing the Insert Statement.

antonaras wrote:
printf("%s\n",(LPCSTR)strSQL);

What is the output of the above line ???

Appu..
"If you judge people, you have no time to love them."

Re: C++ and ADO problem

antonaras30-May-06 23:09

antonaras

30-May-06 23:09

Thanks for the reply NiceNaidu
this is the output that i get:

Insert into Dept(DeptID,Name,OfficeNo,Phone,DeptHead) Values(12Art25622491303Dr.
Antonis Marcou
Error:ΘX↔
Press any key to continue

Re: C++ and ADO problem

antonaras31-May-06 0:04

antonaras

31-May-06 0:04

Hey NiceNaidu
i got it you where right there was a problem with framing the values of the inser statment thanks for helping me out

Re: C++ and ADO problem

NiceNaidu31-May-06 0:12

NiceNaidu

31-May-06 0:12

Ok fine..keep going

Appu..
"If you judge people, you have no time to love them."

Re: C++ and ADO problem

echozeng31-May-06 5:24

echozeng

31-May-06 5:24

i think the program will throw a exception,you can look at the exception for finding out the error informtion.

Set Windows login authentication option programmatically

QuickDeveloper30-May-06 22:20

QuickDeveloper

30-May-06 22:20

hi
i want to set an option in Windows XP & 2000 that user must enter a username & password to login into a computer.(i.e i want to make authentication compulsory )

how to achieve this programmatically??

thanx in advance

"Every morning I go through Forbes list of 40 richest people in the world. If my name is not in there, I go to work..!!!"

Re: Set Windows login authentication option programmatically

Ștefan-Mihai MOGA30-May-06 22:43

Ștefan-Mihai MOGA

30-May-06 22:43

QuickDeveloper wrote:
i want to set an option in Windows XP & 2000 that user must enter a username & password to login into a computer.

I think that's the default behavour in Windows 2000/XP. So, what's the real problem? See you ...

Re: Set Windows login authentication option programmatically [modified]

_anil_30-May-06 22:44

_anil_

30-May-06 22:44

Open your registry and find the key below.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
Create a new string value called "ForceAutoLogon" and set it to 0.

All the above steps you can do programatically Big Grin | :-D

If you want the user should press Ctrl+Alt+Del then
in [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]

Create a new DWORD value, or modify the existing value called 'DisableCAD' to 0

-- modified at 4:44 Wednesday 31st May, 2006
NOTE: Before trying all the above save your registry. Modifying the registry can cause serious problems that may require you to reinstall your operating system
Regards
Anil

Re: Set Windows login authentication option programmatically [modified]

narayanagvs30-May-06 23:30

narayanagvs

30-May-06 23:30

Open your registry and find the key below.
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon]
Create a new string value called "ForceAutoLogon" and set it to 0.

Ofcourse the above steps can be done programmatically but how will the windows detect ForceAutoLogon key when logging in .
Can that be done programmatically????

Re: Set Windows login authentication option programmatically [modified]

_anil_30-May-06 23:44

_anil_

30-May-06 23:44

ForceAutoLogon is a predefined registry key for Windows.
It always check for it at start up. If not present in your registry then it will take default value. So no need to do anything programmatically or manually after setting the key. Big Grin | :-D

Regards
Anil

Re: Set Windows login authentication option programmatically [modified]

narayanagvs31-May-06 0:26

narayanagvs

31-May-06 0:26

Hi Anil,

thanx for ur suggestion

I have another question ..

I need to set AccountLock policies (accountlockout threshold & duration)in
controlpanel\administrative tools\local security policy\Account policy\Account Lockout policy)

Are there any registry keys to set these accountlockout threshold and
accountlockout duration??Could u suggest me on how to do this programmatically.

Thanx

Re: Set Windows login authentication option programmatically [modified]

_anil_31-May-06 1:06

_anil_

31-May-06 1:06

ForceUnlockLogon
LockoutThreshold
LockoutDuration

are the registry key name which can help you. But the actual location I don't know. You can google it or search your registry. I have Window 2000 professional and no administrative tools in control panel. Frown | :-(