Memory Leak?

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Memory Leak?

 
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  #1
Dec 13th, 2005
So I'm writing a program (MFC) that connects to a server w/ windows sockets (YUCK I know). I left it running as part of an endurance test the other day, and my PC ran out of virtual memory. Odd eh? So I ran it again using task manager and noted that it's taking approx. 5,000k or memory everytime it recives and doesn't release the memory until the program is killed. I assume recieves because the amount of memory it takes up is related to how big
C Syntax (Toggle Plain Text) 
  1. char *pBuf = new char[1000025];
is. (See code below) The following is code from the ::OnRecive function in my program.
C Syntax (Toggle Plain Text) 
  1. {
  2. 	char *pBuf = new char[1000025];// yeah yeah i know it's huge!!
  3. 	int iBufSize = 10000024;
  4. 	int iRcvd;
  5. 	CString strRecvd;
  6. 	// Receive the message
  7. 	iRcvd = m_sConnectSocket.Receive(pBuf, iBufSize);
  8. 	// Did we receive anything?
  9. 	if (iRcvd == SOCKET_ERROR)
  10. 	{
  11. 	}
  12. 	else
  13. 	{
  14. 		// Truncate the end of the message
  15. 		pBuf[iRcvd] = NULL;
  16. 		// Copy the message to a CString
  17. 		strRecvd = pBuf;
  18. 		m_pBuf = pBuf;
  19. 		m_strOutput = strRecvd;
  20. 		// Sync the variables with the controls
  21. //		UpdateData(FALSE);
  22. 	}
  23.  
  24. }
So!!! Here in lies the question. Why does it keep taking memory and not releasing it (until the program is killed) and how to I get it to release the memory?
Thanx,
Atrus
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Re: Memory Leak?

 
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Dec 13th, 2005
Because you dont release the memory ? (There is no delete matching the new)... (However most implementations of delete would not actually return the memory to the system anyway, it would just put it in the local free lists)...
*Edit)
If you wanted to allocate lots of memory and be sure to return it to the system you could probably use one winapi function to get you a (several?) fresh page(s), use it and then explicitly return it to the system.
/pern.*/i

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Re: Memory Leak?

 
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  #3
Dec 13th, 2005
Well perni's solution should work. But why cant you use a normal array like
C Syntax (Toggle Plain Text) 
  1. char pBuf = char[1000025]
? It will cleanup itself as it goes out of scope. Saves you a lot of trouble.
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Re: Memory Leak?

 
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Dec 13th, 2005
I suppose you mean char pBuf[LARGE_INTEGER_VALUE], the usual problem with that is you easily get stack overflow due to restrictive stack memory allocation, even if I doubt you need such a large buffer... then again I'm not sure where that limit goes, and it tends to vary between compilers/operative systems (in unix/linux you can usually change it by using limit (or is it ulimit?)).
/pern.*/i

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Re: Memory Leak?

 
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Dec 13th, 2005
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Originally Posted by WolfPack
Well perni's solution should work. But why cant you use a normal array like
C Syntax (Toggle Plain Text) 
  1. char pBuf = char[1000025]
? It will cleanup itself as it goes out of scope. Saves you a lot of trouble.
What's the difference between
C Syntax (Toggle Plain Text) 
  1. char pBuf = char[1000025];
and
C Syntax (Toggle Plain Text) 
  1. char *pBuf = new char[1000025];
when the second one goes out of scope won't it cleanup itself also?

Side note. I tried changing it to what you suggested and I get a bunch of errors.

As clearification<SP>. When the program receives data, it uses say 5,000k. Next time it recieves data it uses another 5,000k. Now my total memory used is 10,000k. This keeps going until I end the program. As you can see this could cause a problem. Eventually I run out of ram. I'm just wondering why? and how to fix it. :cheesy:
Thanx,
Atrus
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Re: Memory Leak?

 
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  #6
Dec 13th, 2005
As I said char pBuf = char[1000025]; is syntax error and does not mean anything...
char pBuf[10000025]; mean declare as local variable and store on stack
char *pBuf = new char[10000025]; mean declare a (local variable) pointer to allocated memory (that must be explicitly deleted)... you do not delete this memory...
all execution paths must include a delete [] pBuf; or hand it over to some other location that must take responsibility for destruction else you will have a memory leak...
/pern.*/i

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Re: Memory Leak?

 
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  #7
Dec 13th, 2005
Yeah my bad. I meant
C Syntax (Toggle Plain Text) 
  1. char pBuf [1000025];
I shouldn't have edited your post on the fly. Sorry about that. It should clear itself when going outof scope.
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Re: Memory Leak?

 
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  #8
Dec 13th, 2005
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Originally Posted by WolfPack
Yeah my bad. I meant
C Syntax (Toggle Plain Text) 
  1. char pBuf [1000025];
I shouldn't have edited your post on the fly. Sorry about that. It should clear itself when going outof scope.
The only problem with that though is that m_sConnectSocket.Receive only takes ( void *lpBuf, int nBufLen, int nFlags = 0) as arguments. if I do what you suggested I get an exception error
Thanx,
Atrus
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Re: Memory Leak?

 
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  #9
Dec 13th, 2005
Well I dont think you would get an error if you pass it as
C Syntax (Toggle Plain Text) 
  1. m_sConnectSocket.Receive( pBuf , 1000025, nFlags)
. A void* should take any kind of pointer.
If it does still give an exception, try doing a cast.
C Syntax (Toggle Plain Text) 
  1. m_sConnectSocket.Receive( (void*)pBuf , 1000025, nFlags)
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Re: Memory Leak?

 
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  #10
Dec 14th, 2005
Still get an exception error, even if I do it both ways.
Thanx,
Atrus
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