Re: Thread synchronization - C / C++ / MFC Discussion Boards

David Crow6-Jul-04 7:15

6-Jul-04 7:15

dNimrod#X wrote:
I was asking if it is possible to know (in a simple way) what the state of INS/OVR is without having to recur to a (main) Keyboard Listener, which in turn would set Global flags on/off.

I take it there is not.

But there is. Try:

if (GetKeyState(VK_INSERT) == 0x01)
    AfxMessageBox("Key is down");
else
    AfxMessageBox("Key is up");

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: Knowing Insert/Overwrite is on/off

0v3rloader6-Jul-04 7:48

0v3rloader

6-Jul-04 7:48

No, you are not understanding my question. Allow me to rephrase:

I need to know whether Text Insert is on or not, meaning if text should be appended (inserted) or overwritten at the current cursor position.

I don't want to know whether a certain key is being pressed or not -- that is out of the scope of the question.

Up till now, the only possible solution I have thought of would be to add a keyboard listener at the application level, which would in turn set 1 boolean variable on/off. Something like: bOverstrike = true/false

To avoid all this, I was wondering if there is either a MFC or a Win32 API function which automatically deals with text overwrite/insert.

Do you [or does anyone] know about such a feature?

David Nimrod

Re: Knowing Insert/Overwrite is on/off

David Crow6-Jul-04 8:04

David Crow

6-Jul-04 8:04

dNimrod#X wrote:
I need to know whether Text Insert is on or not, meaning if text should be appended (inserted) or overwritten at the current cursor position.

Which is exactly the solution I provided you.

dNimrod#X wrote:
I don't want to know whether a certain key is being pressed or not -- that is out of the scope of the question.

Actually, that is the root of the question - whether the INS key is on or off.

dNimrod#X wrote:
Up till now, the only possible solution I have thought of would be to add a keyboard listener at the application level, which would in turn set 1 boolean variable on/off. Something like: bOverstrike = true/false

Implementing a keyboard hook or checking the status when it is needed, the net result is the same - a global variable being set.

"When I was born I was so surprised that I didn't talk for a year and a half." - Gracie Allen

Re: problems with forcibly closing the .exe

#realJSOP6-Jul-04 3:19

#realJSOP

6-Jul-04 3:19

The task manager does not promise cleanup when you end the process from the Processes tab. In fact, it wafrns you that some DLL's may not shut down, etc, etc.

The only reason someone would want to "End Process" on your app is because your app crashed and locked up. The only fix for that is writing better code so that the user doesn't have to use the "End Process" button.

------- sig starts

"I've heard some drivers saying, 'We're going too fast here...'. If you're not here to race, go the hell home - don't come here and grumble about going too fast. Why don't you tie a kerosene rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt

"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

blocking pipe write

A T I F6-Jul-04 2:37

A T I F

6-Jul-04 2:37

I am trying to have a overlapped blocking pipe write so that I can have either data sent signal or a timeout signal... The code I have written is as follows

<br />
	DWORD dwMode = PIPE_READMODE_MESSAGE | PIPE_WAIT;<br />
	BOOL bSuccess = ::SetNamedPipeHandleState(m_hPipe, &dwMode, NULL, NULL);<br />

and my pipe write function have code

<br />
	OVERLAPPED op = {0};<br />
	op.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);<br />
<br />
	bSuccess = ::WriteFile(m_hPipe, lpBufferPos, dwToWrite,<br />
								&dwNumberOfBytesWritten, &op);<br />
		<br />
		if(bSuccess)<br />
		{<br />
                      return TRUE;<br />
		}<br />
		else<br />
		{<br />
			m_dwLastError = ::GetLastError();<br />
			if(m_dwLastError == ERROR_IO_PENDING)<br />
			{<br />
				switch(WaitForSingleObject(op.hEvent, m_dwTimeOut))<br />
				{<br />
				case WAIT_OBJECT_0:<br />
					return TRUE;<br />
					break;<br />
				case WAIT_TIMEOUT:<br />
					m_dwLastError = ::GetLastError();<br />
					return FALSE;<br />
				case WAIT_FAILED:<br />
					m_dwLastError = ::GetLastError();<br />
					return FALSE;<br />
					break;<br />
				}<br />
			}<br />
			else<br />
			{<br />
                                return FALSE;<br />
			}<br />
		}  <br />
	}<br />

The problem that I am facing is that all my Write to pipe function calls keeps returning with TRUE code and the corresponding first Read call in the child process remains locked at the WaitForSingleObject call and then after some write pipe operation in the parent process Read returns with "More data is available" error.

Can anyone direct me what I am doing wrong.

Re: blocking pipe write

A T I F6-Jul-04 2:43

A T I F

6-Jul-04 2:43

PS> what I need is a blocking write with a timeout so that if no read is performed for a specified time the thread unlocks.

Thread synchronization

Kamis6-Jul-04 2:32

Kamis

6-Jul-04 2:32

Hi there! The thing I would like to know is how to lock and unlock a single variable, such as int or double? All these semaphores and events must be declared within a class, but how can I do it with simple types?

Re: Thread synchronization

Antony M Kancidrowski6-Jul-04 3:43

Antony M Kancidrowski

6-Jul-04 3:43

You still have to use at least a Critical Section to lock against while accessing the simple type.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

Re: Thread synchronization

Kamis6-Jul-04 8:30

Kamis

6-Jul-04 8:30

Hmm, I've found InterlockedExchange and I guess that's what I need. By the way, what will happen if I read variable's value in one thread and write to it from another thread using InterlockedExchange, something like this:

bool yes_no; //Common variable

void Thread1Func()
{
bool tmp;
tmp=yes_no;
}

void Thread2Func()
{
InterlockedExchange((LPLONG)&yes_no,true);
}

So, if thread 1 get's to yes_no first is it going to work correctly?

Re: Thread synchronization

Antony M Kancidrowski6-Jul-04 10:34

Antony M Kancidrowski

6-Jul-04 10:34

Assuming that Thread 1 has to wait until Thread 2 has updated the data then no it is not guaranteed to work.

Have you thought about using events?

Wait for the event in Thread 1 (before the read of the variable) then signal the event in Thread 2 after the variable update.

This will ensure the data is current when Thread 1 comes to read it.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

operator new with function free()

xcavin6-Jul-04 0:48

xcavin

6-Jul-04 0:48

Can i delete an object using free(); which was allocated using operator new ?

Re: operator new with function free()

Michael P Butler6-Jul-04 0:53

Michael P Butler

6-Jul-04 0:53

xcavin wrote:
Can i delete an object using free(); which was allocated using operator new ?

I think the first question is why you would want to. Mixing C and C++ memory allocation isn't exactly the best way of writing solid code.

Michael

CP Blog [^]

Re: operator new with function free()

xcavin6-Jul-04 1:19

xcavin

6-Jul-04 1:19

Michael P Butler wrote:
the first question is why you would want to.

I never want to do that. But this was asked to me in an interview. I replied the object's destructor will not be called when free() is used. Smile | :)

I just wanted to know if there is any other views on this issue.

Re: operator new with function free()

Antony M Kancidrowski6-Jul-04 3:34

Antony M Kancidrowski

6-Jul-04 3:34

This is correct, the class destructor isn't called if you attempted to use free(), and therefore your answer is NO! Big Grin | :-D

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fruity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

Question about quering INF file keys?

Behzad Ebrahimi6-Jul-04 0:46

Behzad Ebrahimi

6-Jul-04 0:46

I opend an INF file by SetupOpenInfFile.
To query values and fields of keys I used SetupGetLineText and SetupGetStringField.
I know entry section name. So I can enumarate all other section and key values.
But how can I get a key name by its index number in known section? Confused | :confused:

We know that INF file structure is same as:
[Section1]
Key1=value1
key2=value2
...

Accessing a variable from another class

sugumar6-Jul-04 0:43

sugumar

6-Jul-04 0:43

I have 2 class - CUserDlg,CMenuDlg. I collect a string value from CUserDlg and pass/use this value to/in CMenuDlg.

I define the variable as Public in CUserDlg and Collect value for it.
Public : CString szName;
UserDlg.Cpp:
szName = "Hai";
CDialog::EndDialog(0);
CMenuDlg dlg;
dlg.DoModal();

and close CUserDlg screen and calls CMenuDlg screen.

I define CUserDlg object in MenuDlg header file.
CUserDlg* UserData;

And when I access UserData->szName in CMenuDlg.Cpp file, i get only NULL value.
Pls help me out.

Re: Accessing a variable from another class

Michael P Butler6-Jul-04 1:04

Michael P Butler

6-Jul-04 1:04

sugumar wrote:
I define CUserDlg object in MenuDlg header file.
CUserDlg* UserData;

And when I access UserData->szName in CMenuDlg.Cpp file, i get only NULL value.

Where do you assign the original CUserDlg pointer to the UserData pointer. I usually pass the pointer via the constructor, but your code doesn't appear to do that.

Roughly,

UserDlg.cpp

CUserDlg::OnOK()<br />
{<br />
  CMenuDlg dlg(this)<br />
  dlg.DoModal()<br />
}

CMenuDlg.h

// forward declare<br />
class CUserDlg;<br />
<br />
class CMenuDlg : public CDialog<br />
{<br />
public:<br />
   CMenuDlg(CUserDlg* pUserDlg, CWnd* pParent = NULL);   // standard constructor altered<br />
<br />
private:<br />
  CUserDlg* m_pUserDlg;<br />
}

CMenuDlg.cpp

#include "UserDlg.h"<br />
<br />
CMenuDlg::CMenuDlg(CUserDlg* pUserDlg, CWnd* pParent)<br />
{<br />
  m_pUserDlg = pUserDlg;<br />
}

Then when you want to access szName

void CMenuDlg::SomeFunc()<br />
{<br />
  // sample use<br />
  CString temp = m_pUserDlg->szName;<br />
}

Michael

CP Blog [^]

Re: Accessing a variable from another class

sugumar6-Jul-04 1:20

sugumar

6-Jul-04 1:20

thanks for your immediate response and which also solves my problem.Tnahk You Michael

Re: delete and free

#realJSOP6-Jul-04 0:13

#realJSOP

6-Jul-04 0:13

Did you try it to see if you could?

------- sig starts

"I've heard some drivers saying, 'We're going too fast here...'. If you're not here to race, go the hell home - don't come here and grumble about going too fast. Why don't you tie a kerosene rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt

"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

Re: delete and free

Roger Stoltz6-Jul-04 0:56

Roger Stoltz

6-Jul-04 0:56

As you might know 'new' and 'delete' are C++ keywords for memory allocation and deallocation.
But these small words do more than just memory management.
'new' will call the constructor for the object being created and 'delete' will call the destructor for the object being destroyed. This means that if you create a dynamic object with 'new' and free the memory for that object using 'free', your destructor will not get called and resources allocated by your object will not be freed.
Technically I suppose you could use 'free' given that your class doesn't have to free up any memory in its destructor, but then you have another problem.
When building for Debug some extra bytes will get allocated using 'new' to be able to discover memory leaks and so forth. If you don't use 'delete' at least this memory checking won't work and there is a great risk that the application will crash.

In short:
ALWAYS use 'delete' when you have allocated memory using 'new'.
Using 'free' when deallocating memory allocated using 'new' might work under VERY special circumstances but trying to use this technique would be begging for problems in my opinion.

--
Roger

Re: delete and free

xcavin6-Jul-04 1:25

xcavin

6-Jul-04 1:25

Thanks. My 5 marks.
Espically for that Debug build problem.

Help from VB programmers

#realJSOP5-Jul-04 23:34

#realJSOP

5-Jul-04 23:34

I posted the following in the VB forum but nobody seems to be interested (or has the ability to help).

------------------------------------

I've written a DLL in VC6 (C++), and I think it's going to be used by a VB programmer. Knowing this ahead of time, I return variants from all exported functions.

I've tested the DLL with a C++ program, but I don't have VB installed and don't care to install it, so I'm looking for some help from someone that already has VB installed and knows how to use the language.

1) What do I need give the VB programmer in terms of info about the exported functions in the DLL?

2) Can someone here download and try the DLL in a VB program? If so, go here to download the DLL (includes the C++ test program source):

http://www.paddedwall.org/john/programmer/code/d3dlltest.zip

The DLL is designed to find different versions of the racing sim I play on the PC. It does this by looking for specific registry entries. For all but maybe one other person here, the DLL should reveal that none of the sims are installed.

[EDIT]
This DLL is not a COM DLL. It is not an ActiveX DLL. It will never be either of the those. Don't bring it up. Don't suggest it. Don't argue the point, because I'm truly not the least bit interested. I will not treat suggestions along those lines with sensitivity, caring, or kind remindeers. I'm not asking for opinions, different ways to do something, or anything like that. I am asking for facts in response to the questions I posted in this message. You have been warned.
[/EDIT]

------- sig starts

"I've heard some drivers saying, 'We're going too fast here...'. If you're not here to race, go the hell home - don't come here and grumble about going too fast. Why don't you tie a kerosene rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt

"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

Re: Help from VB programmers

Duncan Edwards Jones6-Jul-04 0:15

Duncan Edwards Jones

6-Jul-04 0:15

1) What do I need give the VB programmer in terms of info about the exported functions in the DLL?

The header file should be enough. Note that your exports will need to be in CDECL (assuming your dll is a non-ActiveX one...)

'--8<------------------------
Ex Datis:
Duncan Jones
Merrion Computing Ltd

Re: Help from VB programmers

#realJSOP6-Jul-04 0:56

#realJSOP

6-Jul-04 0:56

The DLL is NOT an activeX(crement) DLL.

I used a def file for exports and did the following for each exported function:

VARIANT PASCAL EXPORT FunctionName()

VB doesn't use header files (that I know of) so that reference kinda confuses me.

As far as I can tell, the PASCAL macro expands out to "__stdcall".

What I need is for someone to try using the DLL from a VB program. All of the exported functions are tested in the sample app enclosed in the RAR file.

------- sig starts

"I've heard some drivers saying, 'We're going too fast here...'. If you're not here to race, go the hell home - don't come here and grumble about going too fast. Why don't you tie a kerosene rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt

"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001

Re: Help from VB programmers

Duncan Edwards Jones6-Jul-04 1:47

Duncan Edwards Jones

6-Jul-04 1:47

VB doesn't use header files (that I know of) so that reference kinda confuses me.

No - but you can convert the C++ function def from the header file into a VB import declaration.

e.g.:-

<br />
/* dbgHelp.h */<br />
BOOL SymGetSearchPath(<br />
  HANDLE hProcess,<br />
  PSTR SearchPath,<br />
  DWORD SearchPathLength);<br />

becomes

<br />
Public Declare Function SymGetSearchPath Lib "dbghelp.dll" ( _<br />
        ByVal hProcess As Long, _<br />
        ByVal SearchPath As String, _<br />
        ByVal SearchPathLength As String) As Long<br />

'--8<------------------------
Ex Datis:
Duncan Jones
Merrion Computing Ltd

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