C / C++ / MFC

1-Jan-07 2:45

if a class is to overload both the prefix and postfix operators, the sigs usually look like this:

const Counter& operator++ (); // prefix
const Counter operator++ (int); // postfix

my question is why is the prefix returning a reference while the latter returns by value?

thank you.

I am a SysAdmin, I battle my own daemons.

Re: prefix vs postfix

Nemanja Trifunovic1-Jan-07 5:22

Nemanja Trifunovic

1-Jan-07 5:22

See here[^]

Programming Blog
utf8-cpp

IOCP And WSANOBUFS Error

Polity4h1-Jan-07 2:32

1-Jan-07 2:32

Hi,
I'm writing a server application using UDP and the I/O Completion port. I red some articles and i know the things about it.
My application scans a list of servers, requests some information, unpacks the information and stores the information, this is a process in loop. However, after a while i get the 10055 Error or better said WSANOBUFS. Now i red that that means that there cant be made any more locks ( source[^] ) I cant quit seem to find where the error takes place, there might be a sort of loop in locking where the the unlock never hits, but i dont know where that would be then. Is there any way to detect a possible deadlock? or do you know something else that might be wrong? Thanks already

-Koen

Mark Salsbery1-Jan-07 8:52

Mark Salsbery

1-Jan-07 8:52

Where are you getting the WSAENOBUFS error? On a send, receive, connect?

If on a send, have you disabled send buffering for the socket?

Are you using IOCP for sends, recvs, connects? All overlapped operations?

Polity4h1-Jan-07 11:01

1-Jan-07 11:01

int res = WSARecvFrom(m_sSocket, &m_wsaBuf, 1, reinterpret_cast<LPDWORD>(&buflen), &temp, reinterpret_cast<sockaddr*>(&m_objAddress), &sockaddr_len, &m_objOverlapped, NULL);

There i get the error 10055, Sending goes just fine.
Since im using UDP im not connecting. Next to that, i dont use overlapped operations everywhere, i got a mysql class wich just sends a status update every 10 seconds, and a remote manager class wich uses TCP. both the mysql and the rmanager are using normal winsock so without overlapped operations.

<br />
					m_sSocket = socket(AF_INET, SOCK_DGRAM, 0);<br />
					m_objAddress.sin_family = AF_INET;<br />
					m_objLocalAddress.sin_family = AF_INET; <br />
					m_objLocalAddress.sin_addr.s_addr = htonl(INADDR_ANY);<br />
					m_objLocalAddress.sin_port = 0;    <br />
					m_hIOCP = hIOCP;<br />
					if (bind(m_sSocket, reinterpret_cast<sockaddr*>(&m_objLocalAddress),  sizeof(m_objLocalAddress))==SOCKET_ERROR){<br />
						TRACE("Error binding localaddress with the socket, Error: %i\n", WSAGetLastError());<br />
					}<br />
					if (CreateIoCompletionPort(reinterpret_cast<HANDLE>(m_sSocket), hIOCP, reinterpret_cast<DWORD>(const_cast<CVirtualSession*>(this)), 0)==NULL){ //Error binding?<br />
						TRACE("Error binding Session to the main object, Error: %i\n", WSAGetLastError());<br />
						return;<br />
					}

Here i initialize is UDP session, there are like 400 udp virtual sessions continiously sending and recieving data. the first minut it goes all well, but after that, every sessions returns the error 10055 on recieving

)...
Windows Sockets 2.0: Write Scalable Winsock Apps Using Completion Ports[^]
INFO: Design Issues When Using IOCP in a Winsock Server[^]

Mark Salsbery1-Jan-07 15:14

Mark Salsbery

1-Jan-07 15:14

This may or may not be the problem, but based on what I've seen it's the first thing that comes
to mind. I hope this helps a bit...

Unless you always keep enough receive buffers queued in your IOCP then the socket can receive
datagrams faster than you are pulling them out of its buffer.

If the socket is not "connected" (for UDP that just means all datagrams will be ignored except
from the "connected" address) then the socket's recv buffer gets filled with every UDP datagram it
sees on the network. You need to pull them out fast enough to keep enough buffer space for
receives.

One option is to use a connected socket to receive UDP datagrams on. The drawback is you'd need
400 sockets, or one for every session as you described.

Another option is to always have a pool of overlapped WSARecvFrom() calls pushed on the IOCP
stack so there will always be one available when a datagram is received. You could use the
FD_READ notification to help notify a thread that data has been received on the socket and make
sure there's a pending overlapped receive operation ready to accept the data.

Also make sure your IOCP is properly "tuned" with the right amount of threads in the pool to
most efficiently handle all the received datagrams.

These articles may be helpful too (you may have seen them already - I keep them bookmarked for
any IOCP troubles I encounter Smile | :)

Polity4h2-Jan-07 0:27

2-Jan-07 0:27

thanks, i havent solved the problem yet however i didnt try your possible solutions so Smile | :)

I'll working on it as soon as my job ends. i'll tell you how it goes as soon as there's some result. thanks again

Polity4h2-Jan-07 6:25

2-Jan-07 6:25

If the socket is not "connected" (for UDP that just means all datagrams will be ignored except
from the "connected" address) then the socket's recv buffer gets filled with every UDP datagram it
sees on the network. You need to pull them out fast enough to keep enough buffer space for
receives.

I tried some solutions but i cant seem to get them working. Its probably my lack of experiance but well,
The fundamental code:

<br />
				while (1){ <br />
					BOOL bIORet = GetQueuedCompletionStatus ( // Get a completed IO request<br />
						   pThis->m_hIOCompiltionPort,<br />
						   &dwIoSize,<br />
						   reinterpret_cast<LPDWORD>(pThis),<br />
						   &ptrOverlapped, INFINITE);<br />
					if (!bIORet){<br />
						TRACE("Winsock error code: %i\n", GetLastError());<br />
						Gameye::Library::Thread::CMPThread::Sleep(0);<br />
					}<br />
					else{<br />
						ptrSession = static_cast<CVirtualSession*>(ptrOverlapped->Pointer);<br />
						CAbstractServerClass* ptrGameClass = (*pThis->m_ptrGameManager)[ptrSession->getNDServer()->GameID];<br />
						if (ptrGameClass == NULL){<br />
							TRACE("Game is unknown, probably removed\n");<br />
						}<br />
						else{<br />
							objToolset.Session = ptrSession;<br />
							switch(ptrSession->getTask()){<br />
								case RequestSend: //Request to send a packet<br />
									if (WSASendTo(sSocket, <br />
										ptrSession->getWSABuffer(),<br />
										1,<br />
										reinterpret_cast<LPDWORD>(&ptrSession->getWSABuffer()->len),<br />
										0,reinterpret_cast<sockaddr*>(ptrSession->getAddress()),<br />
										sizeof(sockaddr_in),<br />
										ptrSession->getOverlapped(), NULL) == -1)<br />
									{<br />
										int iErrorCode = WSAGetLastError();<br />
										if (iErrorCode != 997){ //997 =  Data is already recieved<br />
											TRACE("Sending failed because: %i\n", WSAGetLastError());<br />
											break;<br />
										}<br />
									}<br />
									ptrSession->setStatus(AfterSend);<br />
									break;<br />
								case RequestRecieve: //Request to recieve a packet<br />
									if (WSARecvFrom(sSocket, <br />
										ptrSession->getWSABuffer(),<br />
										1,<br />
										reinterpret_cast<LPDWORD>(&ptrSession->getWSABuffer()->len),<br />
										&iTemp,reinterpret_cast<sockaddr*>(ptrSession->getAddress()),<br />
										&iSockAddrSize,<br />
										ptrSession->getOverlapped(), NULL) == -1)<br />
									{<br />
										int iErrorCode = WSAGetLastError();<br />
										if (iErrorCode != 997){ //997 =  Data is already recieved<br />
											TRACE("Recieving failed because: %i\n", WSAGetLastError());<br />
											ptrSession->setStatus(AfterRecieve);<br />
										}<br />
									}<br />
									ptrSession->setStatus(AfterRecieve);<br />
									break;			<br />
								case AfterSend: //Call sending event<br />
									ptrSession->incSendBytes(dwIoSize);<br />
									ptrGameClass->RetrieveServerInfo(ptrSession->getNDServer(), &objToolset);<br />
									break;<br />
								case AfterRecieve: //Call receiving event<br />
									ptrSession->incRecvBytes(dwIoSize);<br />
									if (ptrGameClass->UnpackServerInfo(ptrSession->getNDServer(), &objToolset) == 0){//Session is finished!<br />
										ptrSession->Finish();<br />
									}<br />
									break;<br />
								case Finishing:<br />
									pThis->m_objSql.AddGame(ptrSession->getNDServer());<br />
									break;<br />
								default:<br />
									break; //Who knows?<br />
							}<br />
						}<br />
					}

Most calls should be clear. the events i call are simpel functions, they should return in a inch of a sec, next to that, i can have 10 workerthreads running and still i get the same error. some sessions come out alive but most of them just gives the known error on recieve. You also see that after every send, a call to WSARecvFrom is been made. its not directly but again with the inch of a second.

Also, with 10 sessions, 2/3 sessions returns the error on recieve the rest just works fine. with 400 sessions, a few return with the error and a few dont. that indicates that the recieve buffer aint full right?

Mark Salsbery2-Jan-07 7:07

Mark Salsbery

2-Jan-07 7:07

You get a completion packet indicating "RequestRecieve" and in response you call WSARecvFrom()
before calling ptrSession->setStatus(AfterRecieve);

Chances are pretty good that another thread has already processed the completion of the
WSARecvFrom() call before you can even check the error code! Smile | :)

So, you'll get ANOTHER RequestRecieve before you have a chance to set the session status to
AfterRecieve.

Make sense?

In other words, you probably want to call ptrSession->setStatus(AfterRecieve) BEFORE you call
WSARecvFrom().

Also, use WSA_IO_PENDING instead of 997 so I can read your code haha Smile | :)

I don't have all the WSAE
codes memorized yet Poke tongue | ;-P

Polity4h2-Jan-07 7:17

2-Jan-07 7:17

Nope, that aint the proble. would be really quick Wink | ;)

and srry about the code, its just a test project. when i got it all working i'm gonna merch it and mostly rewrite it.
Thanks anyway

console app in VS2003

swjam1-Jan-07 2:01

1-Jan-07 2:01

hi,

I can't seem to create a simple c++ console application in VStudio .NET 2003. Whenever I create the console application provided in the template projects, I can't compile with for example, the system function cout
What could I be doing wrong?
If this can't be fixed, is there going to be a problem if I install both VStudio6.0 and VStudio.NET 2003 in the same machine/OS?

Thank you and Happy New Year

I'm a SysAdmin, I battle my own daemons.

Jonathan [Darka]1-Jan-07 2:16

Jonathan [Darka]

1-Jan-07 2:16

Don't forget to include the iostream header file.

#include <iostream>

Darka [Xanya]

"I am not a slave to a god that doesn't exist."

swjam1-Jan-07 2:22

1-Jan-07 2:22

Thanks but I have done that. Besides it already includes "stdafx.h" Confused | :confused:

See the FAQ
2.1 I'm trying to use a standard C++ library class (like cout, cin, or string) but the compiler gives an undeclared identifier error (C2065) on those names. Why?[^]

Michael Dunn1-Jan-07 10:00

Michael Dunn

1-Jan-07 10:00

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

LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ

Ford, what's this fish doing in my ear?

swjam1-Jan-07 15:18

Re: "friend" class question

1-Jan-07 15:18

i thought the problem was being caused by the new vstudio .net (i am new to .net)
anyhow, this helped... thanks!

double casting

Hadi Dayvary1-Jan-07 1:43

Hadi Dayvary

1-Jan-07 1:43

Hi Why after this piece of code value of d is : 3.4560000896454 ? Confused | :confused:

float f = (float)3.456;<br />
double d = (double)f;

Thanks

Re: double casting

Gary R. Wheeler1-Jan-07 4:33

Gary R. Wheeler

1-Jan-07 4:33

In computers, real values are only approximations; there are only a limited number of bits used to represent fractional values. You need to keep that in mind when dealing with float and double type values. The double type includes a larger number of bits (64 in the Windows world) than the float type (32).

When you do the conversion from one to the other via the (double) cast operator, those extra bits come into play. In a float value, 3.456 may have a string representation of 3.456000. A double version of that value adds additional significant digits, which results in the 3.456000089454 that you are seeing.

Software Zen: delete this;

Fold With Us![^]

"friend" class question

eli150219791-Jan-07 1:04

eli15021979

1-Jan-07 1:04

Hi,

I have a base class(lets say class X) which is a "friend" of another class(lets say Class Y).
Using the base class(class X) I can access private members in the other class.
My problem is that I derived a new class(class Z) from the base class,and I need to use a private method from class Y.

I thought that if class X is a friend of class Y , then all the derived classes of class X are also friend of class Y , but I realized that I was wrong.

My problem is that I can't modify class X and class Y because it is our core.

anyone?
With best regards,
Eli

Polity4h1-Jan-07 4:10

1-Jan-07 4:10

declare the friend as protected

Data Exchange

Shouvik Das1-Jan-07 0:16

Shouvik Das

1-Jan-07 0:16

I've made an SDI Appl with DB Support by MFC Wizard. now in an ADmin module i validat the password supplied by the Administrator and open a Modal Dlg Box with certain Edit Text fields radio buttons.

I've 4 buttons in it.
1) Add
2) Inventory
3) Edit
4) Exit.

On addition i want to add the values in these fields to the DB. but i'm not able to add the member variables to m_pSet-><Field_Name> values to that of the edit text boxes. also I ve a field as accession number(1111-9999) which is a p_key. while we add an item the greatest acc. no. has to be read n a next gr8er no needs to be gen. associated with the item.

The basic prob is how to update data without closing the Dlg Box.

Sigh | :sigh:

I know this is a lengthy one...plz bear with it. Blush | :O

Success makes life easier. It doesn't make living easier.

SH UVIK

PJ Arends1-Jan-07 7:48

PJ Arends

1-Jan-07 7:48

shouvik.d wrote:
The basic prob is how to update data without closing the Dlg Box.

Use a modeless dialog.

http://msdn2.microsoft.com/en-us/library/hf0yazk7(vs.80).aspx[^]

You may be right
I may be crazy
-- Billy Joel --

Within you lies the power for good, use it!!!

Shouvik Das1-Jan-07 16:42

Shouvik Das

1-Jan-07 16:42

No i cant let a user access the SDI window when he/she is accessing the Dlg Box.

I just used DDX but still until the Modal Dlg Box Closes I'm not able to invoke update to DB.

how to do it Confused | :confused:

Success makes life easier. It doesn't make living easier.

SH UVIK

Cristian Amarie2-Jan-07 3:58

Cristian Amarie

2-Jan-07 3:58

shouvik.d wrote:
No i cant let a user access the SDI window when he/she is accessing the Dlg Box.

Disable the SDI window while the dialog box is active. MFC simulates modal dialog boxes exactly in this way, creating a modeless dialog box from template, disabling main window if any, display the dialog, and reenable the main window after.

Another possibility is to inform application from the modal dialog to perform the update.
This way you don't have to wait the dialog to close, such as in

void CDlg::OnButtonClicked()
{
  // gather data to update in a structure or class
  CData data;
  // ...

  static_cast<CSDIApp *>(AfxGetApp())->updateDatabase(&data);
}

and

void CSDIApp::updateDatabase(CData *pData)
{
  // update in database using pData members
}