C / C++ / MFC

Tomasz Sowinski30-Aug-02 1:06

30-Aug-02 1:06

limits.h for integers and float.h for floating point numbers.

Tomasz Sowinski -- http://www.shooltz.com

Free your mind and your ass will follow.

markkuk30-Aug-02 1:16

markkuk

30-Aug-02 1:16

That's the C solution, but in C++ you can use the numeric_limits class defined in <limits>. for example:

#include <limits>
using namespace std;
// when you need a limit, use:
numeric_limits<int>::min();
numeric_limits<float>::max();
//etc...

Tomasz Sowinski30-Aug-02 1:29

30-Aug-02 1:29

markkuk wrote:
That's the C solution, but in C++ you can use the numeric_limits class defined in <limits>.

Good point. But I have to admit that I hate to type std::numeric_limits<int>::max() Smile | :)

Tomasz Sowinski -- http://www.shooltz.com

Free your mind and your ass will follow.

Zizilamoroso30-Aug-02 3:41

Zizilamoroso

30-Aug-02 3:41

INT_MAX is indeed much shorter Wink | ;-)

tnx!

[VISUAL STUDIO 6.0] [MFC] [WIN98/2]

Bluute tette! Dead | X|

Memory leakages

Anonymous30-Aug-02 0:56

Anonymous

30-Aug-02 0:56

I've seen many good articles here at CP, and below many articles, a famous comment is given that this code has memory leakage.

Can any one explain me how can we check that our application is causing memory leakages. I had idea that main cause of memory leakage is dynamic memory allocation using new and then not using delete. But IMHO this is not always true. So someone please tell me what is memory leakage, what are its causes and how can we determine that our application executable is causing memory leakage.

Re: Memory leakages

Tomasz Sowinski30-Aug-02 1:09

TCP header checksum calculation

30-Aug-02 1:09

Memory leak happens when you allocate somthing with new/alloc and forget to free the memory block with appropriate delete/free.

There are commercial tools for detecting memory leaks and other defects in C++ programs (like reading uninitialized memory) - most notably Compuware's BoundsChecker and Rational's Purify.

Tomasz Sowinski -- http://www.shooltz.com

Free your mind and your ass will follow.

Re: Memory leakages

pépé30-Aug-02 4:11

pépé

30-Aug-02 4:11

There is also a very basic detection/debugging with _CrtDumpMemoryLeaks() and _CrtSetBreakAlloc() in crtdbg.h

"640K ought to be enough for anybody."
Bill Gates

Re: Memory leakages

Anders Molin30-Aug-02 12:40

Anders Molin

30-Aug-02 12:40

You don't have to call _CrtDumpMemoryLeaks() and _CrtSetBreakAlloc() yourself...

Just call _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF | _CRTDBG_CHECK_ALWAYS_DF); in the start of your program, and it will detect all memory leaks...

[edit]
This also checks for memory ower/underwrites...
[/edit]

And if you define _CRTDBG_MAP_ALLOC before any includes (in the top of stdafx.h) you also get the sourcefile and linenumber where you allocated the not-free'ed memory. Wink | ;)

- Anders

Money talks, but all mine ever says is "Goodbye!"

AIDS30-Aug-02 0:56

AIDS

30-Aug-02 0:56

Hi All,

I got stuck with TCP header checksum calculation.
RFC 793 says checksum is calculated using the same algorithm as IP header checksum and includes 96-bit pseudo header + data.
I have written a checksum calculation function, and it works well for IP headers, but when I apply it to the TCP packet the function produces wrong results.
I have captured a TCP packet from my network, and put it into my
test program. There are 2 checksum functions in the code: Checksum and ChecksumRFC. The last one is taken from RFC1071.
The code is for Windows 2000, VC6.0

Could anyone explain me what I do wrong?

<br />
#include <stdio.h><br />
#include <windows.h><br />
<br />
<br />
<br />
// to ensure memory alignment<br />
#include <pshpack1.h><br />
<br />
typedef struct _IP_HEADER<br />
{<br />
	UCHAR  HeaderLength :4;	 // Header length in 32-bit words<br />
	UCHAR  Version      :4;	 // IP version<br />
<br />
	UCHAR  TypeOfService;	 // <br />
	USHORT TotalLength;		 // Total datagram (header + data) length in bytes<br />
	USHORT Identification;	 // <br />
	USHORT FlagsFragment;    // Flags (3 bits) + Fragment position (13bits) in datagram (in 64-bit units)<br />
	UCHAR  TimeToLive;		 //<br />
	UCHAR  Protocol;		 // Next level protocol <br />
	USHORT Checksum;		 // IP header checksum<br />
	ULONG  SourceAddress;	 // Source address<br />
	ULONG  DestAddress;		 // Destination address<br />
} IP_HEADER, *PIP_HEADER;<br />
<br />
<br />
//<br />
// Next level protocol IDs<br />
//<br />
#define IPPROTO_TCP 6<br />
#define IPPROTO_UDP 17<br />
<br />
<br />
//<br />
// TCP Header (rfc 793)<br />
//<br />
<br />
typedef struct _TCP_HEADER<br />
{<br />
	USHORT SourcePort;	//<br />
	USHORT DestPort;	//<br />
	ULONG  SeqNumber;	// Sequence number<br />
	ULONG  AckNumber;	// Acknowledge number<br />
	UCHAR  Reserved :4;	// Reserved must be zero<br />
	UCHAR  Offset   :4;	// TCP Header size in 32-bit words<br />
	UCHAR  FIN      :1;	// No more data from Sender	<br />
	UCHAR  SYN      :1;	// Synchronize sequence number<br />
	UCHAR  RST      :1;	// Reset the connection<br />
	UCHAR  PSH      :1;	// Push function<br />
	UCHAR  ACK      :1;	// Acknowledgment field significant<br />
	UCHAR  URG      :1;	// Urgent pointer field significant<br />
	UCHAR  Reserved1:1;	// <br />
	UCHAR  Reserved2:1;	//<br />
	USHORT Window;		// Number of data octets which the sender of this segment is willing to accept<br />
	USHORT Checksum;	// Checksum of header + data<br />
	USHORT Urgent;		// <br />
} TCP_HEADER, *PTCP_HEADER;<br />
<br />
<br />
//<br />
// TCP pseudo header for checksum calculation<br />
//<br />
<br />
// to ensure memory alignment<br />
typedef struct _TCP_PSEUDOHEADER<br />
{<br />
	ULONG  SourceAddress;	// source IP address<br />
	ULONG  DestAddress;		// destination IP address<br />
	UCHAR  Zero;			// must be 0<br />
	UCHAR  Protocol;		// protocol - always 0x6<br />
	USHORT TcpLength;		// length of TCP header + data<br />
} TCP_PSEUDOHEADER, *PTCP_PSEUDOHEADER;<br />
<br />
#include <poppack.h><br />
<br />
<br />
//<br />
// For debug purposes only. Dumps the Ip header's content<br />
// to the debugger window<br />
//<br />
VOID DumpIPHeader( PIP_HEADER IpHeader )<br />
{<br />
	printf <br />
		(<br />
			"=== IP Header Dump Begin ===\n"<br />
			"Header length (32bit words): %d\n"<br />
			"Version:                     %d\n"<br />
			"TypeOfService:               %d\n"<br />
			"TotalLength:                 %d\n"<br />
			"Identification:            0x%0X\n"<br />
			"Flags/Fragment:            0x%X\n"<br />
			"TimeToLive:                0x%X\n"<br />
			"Protocol:                  0x%X\n"<br />
			"Checksum:                  0x%X\n"<br />
			"Source:                    0x%08X\n"<br />
			"Dest:                      0x%08X\n"<br />
			,<br />
			IpHeader->HeaderLength,<br />
			IpHeader->Version, <br />
			IpHeader->TypeOfService, <br />
			ntohs( IpHeader->TotalLength ), <br />
			IpHeader->Identification, <br />
			IpHeader->FlagsFragment, <br />
			IpHeader->TimeToLive, <br />
			IpHeader->Protocol, <br />
			IpHeader->Checksum, <br />
			IpHeader->SourceAddress, <br />
			IpHeader->DestAddress<br />
	);<br />
}<br />
<br />
VOID DumpTCPHeader( PTCP_HEADER TcpHeader )<br />
{<br />
 <br />
	printf	(<br />
			"=== TCP Header Dump Begin ===\n"<br />
			"Source port: 0x%4X\n"<br />
			"Dest port  : 0x%4X\n"<br />
			"Sequence   : 0x%0X\n"<br />
			"Acknowledge: 0x%0X\n"<br />
			"Offset     : %d\n"<br />
			"SYN        : 0x%X\n"<br />
			"Window     : 0x%X\n"<br />
			"Checksum   : 0x%X\n"<br />
			"Urgent   : 0x%X\n"<br />
			"ACK        : 0x%X\n"<br />
			"PSH        : 0x%X\n"<br />
			,<br />
			TcpHeader->SourcePort, <br />
			TcpHeader->DestPort, <br />
			ntohl(TcpHeader->SeqNumber),<br />
			ntohl(TcpHeader->AckNumber), <br />
			TcpHeader->Offset,<br />
			TcpHeader->SYN, <br />
			TcpHeader->Window, <br />
			TcpHeader->Checksum,<br />
			TcpHeader->Urgent,<br />
			TcpHeader->ACK, <br />
			TcpHeader->PSH<br />
<br />
	);<br />
}<br />
<br />
<br />
UCHAR Packet[478] =<br />
{<br />
	0x45,  0x00, <br />
	0x01,  0xDE,  0x50,  0xA8,  0x40,  0x00,  0x80,  0x06,  0xC5,  0x8E,  0xC0,  0xA8,  0x04,  0x30,  0x14,  0x0A, <br />
	0x0A,  0x01,  0x0B,  0x27,  0x00,  0x50,  0xAC,  0x78,  0xD2,  0x04,  0xB0,  0x9A,  0x29,  0x07,  0x50,  0x18,<br />
	0x44,  0x70,  0xE3,  0x3F,  0x00,  0x00,  0x47,  0x45,  0x54,  0x20,  0x2F,  0x74,  0x65,  0x73,  0x74,  0x20,<br />
	0x48,  0x54,  0x54,  0x50,  0x2F,  0x31,  0x2E,  0x31,  0x0D,  0x0A,  0x41,  0x63,  0x63,  0x65,  0x70,  0x74,<br />
	0x3A,  0x20,  0x69,  0x6D,  0x61,  0x67,  0x65,  0x2F,  0x67,  0x69,  0x66,  0x2C,  0x20,  0x69,  0x6D,  0x61,  <br />
	0x67,  0x65,  0x2F,  0x78,  0x2D,  0x78,  0x62,  0x69,  0x74,  0x6D,  0x61,  0x70,  0x2C,  0x20,  0x69,  0x6D,<br />
	0x61,  0x67,  0x65,  0x2F,  0x6A,  0x70,  0x65,  0x67,  0x2C,  0x20,  0x69,  0x6D,  0x61,  0x67,  0x65,  0x2F,<br />
	0x70,  0x6A,  0x70,  0x65,  0x67,  0x2C,  0x20,  0x61,  0x70,  0x70,  0x6C,  0x69,  0x63,  0x61,  0x74,  0x69,  <br />
	0x6F,  0x6E,  0x2F,  0x76,  0x6E,  0x64,  0x2E,  0x6D,  0x73,  0x2D,  0x65,  0x78,  0x63,  0x65,  0x6C,  0x2C,<br />
	0x20,  0x61,  0x70,  0x70,  0x6C,  0x69,  0x63,  0x61,  0x74,  0x69,  0x6F,  0x6E,  0x2F,  0x6D,  0x73,  0x77,<br />
	0x6F,  0x72,  0x64,  0x2C,  0x20,  0x61,  0x70,  0x70,  0x6C,  0x69,  0x63,  0x61,  0x74,  0x69,  0x6F,  0x6E,<br />
	0x2F,  0x76,  0x6E,  0x64,  0x2E,  0x6D,  0x73,  0x2D,  0x70,  0x6F,  0x77,  0x65,  0x72,  0x70,  0x6F,  0x69,<br />
	0x6E,  0x74,  0x2C,  0x20,  0x2A,  0x2F,  0x2A,  0x0D,  0x0A,  0x41,  0x63,  0x63,  0x65,  0x70,  0x74,  0x2D,<br />
	0x4C,  0x61,  0x6E,  0x67,  0x75,  0x61,  0x67,  0x65,  0x3A,  0x20,  0x65,  0x6E,  0x2D,  0x67,  0x62,  0x0D,<br />
	0x0A,  0x41,  0x63,  0x63,  0x65,  0x70,  0x74,  0x2D,  0x45,  0x6E,  0x63,  0x6F,  0x64,  0x69,  0x6E,  0x67,  <br />
	0x3A,  0x20,  0x67,  0x7A,  0x69,  0x70,  0x2C,  0x20,  0x64,  0x65,  0x66,  0x6C,  0x61,  0x74,  0x65,  0x0D,<br />
	0x0A,  0x55,  0x73,  0x65,  0x72,  0x2D,  0x41,  0x67,  0x65,  0x6E,  0x74,  0x3A,  0x20,  0x4D,  0x6F,  0x7A,<br />
	0x69,  0x6C,  0x6C,  0x61,  0x2F,  0x34,  0x2E,  0x30,  0x20,  0x28,  0x63,  0x6F,  0x6D,  0x70,  0x61,  0x74,  <br />
	0x69,  0x62,  0x6C,  0x65,  0x3B,  0x20,  0x4D,  0x53,  0x49,  0x45,  0x20,  0x35,  0x2E,  0x30,  0x31,  0x3B,<br />
	0x20,  0x57,  0x69,  0x6E,  0x64,  0x6F,  0x77,  0x73,  0x20,  0x4E,  0x54,  0x20,  0x35,  0x2E,  0x30,  0x29,<br />
	0x0D,  0x0A,  0x48,  0x6F,  0x73,  0x74,  0x3A,  0x20,  0x32,  0x30,  0x2E,  0x31,  0x30,  0x2E,  0x31,  0x30,  <br />
	0x2E,  0x31,  0x0D,  0x0A,  0x43,  0x6F,  0x6E,  0x6E,  0x65,  0x63,  0x74,  0x69,  0x6F,  0x6E,  0x3A,  0x20,<br />
	0x4B,  0x65,  0x65,  0x70,  0x2D,  0x41,  0x6C,  0x69,  0x76,  0x65,  0x0D,  0x0A,  0x43,  0x6F,  0x6F,  0x6B,<br />
	0x69,  0x65,  0x3A,  0x20,  0x4D,  0x53,  0x41,  0x53,  0x50,  0x43,  0x6C,  0x69,  0x65,  0x6E,  0x74,  0x53,<br />
	0x69,  0x64,  0x65,  0x43,  0x6F,  0x6C,  0x6F,  0x72,  0x3D,  0x38,  0x30,  0x38,  0x30,  0x30,  0x30,  0x3B,<br />
	0x20,  0x4D,  0x53,  0x41,  0x53,  0x50,  0x48,  0x54,  0x4D,  0x4C,  0x43,  0x6F,  0x6C,  0x6F,  0x72,  0x3D,<br />
	0x25,  0x32,  0x33,  0x46,  0x46,  0x38,  0x30,  0x38,  0x30,  0x3B,  0x20,  0x41,  0x53,  0x50,  0x53,  0x45,<br />
	0x53,  0x53,  0x49,  0x4F,  0x4E,  0x49,  0x44,  0x51,  0x47,  0x47,  0x47,  0x47,  0x52,  0x43,  0x43,  0x3D,  <br />
	0x4D,  0x46,  0x42,  0x4C,  0x49,  0x4C,  0x4D,  0x42,  0x4B,  0x48,  0x4A,  0x41,  0x47,  0x48,  0x47,  0x50,  <br />
	0x4F,  0x46,  0x41,  0x43,  0x47,  0x45,  0x4E,  0x49,  0x0D,  0x0A,  0x0D,  0x0A<br />
};<br />
<br />
<br />
USHORT Checksum( PUCHAR Data, USHORT Length )<br />
{<br />
	ULONG Sum = 0;<br />
	USHORT ShortSum = 0;<br />
	PUSHORT WordData = (PUSHORT) Data;<br />
	USHORT WordCount = Length >> 1;<br />
<br />
	while( WordCount-- )<br />
		Sum += *WordData++;<br />
<br />
	if( Length & 1 )<br />
		Sum += *(PUCHAR)WordData;<br />
<br />
	Sum = (USHORT) Sum + (Sum >> 16) & 0xFFFF;<br />
	ShortSum = (USHORT) Sum + (USHORT)(Sum >> 16);<br />
	<br />
	return (ShortSum != 0xFFFF) ? ~ShortSum : ShortSum;<br />
} <br />
<br />
USHORT ChecksumRFC( PUCHAR Data, USHORT Length )<br />
{<br />
	ULONG Sum = 0;<br />
	PUSHORT WD = (PUSHORT) Data;<br />
<br />
	while( Length > 1 )<br />
	{<br />
		Sum += * WD++;<br />
		Length -= 2;<br />
	}<br />
<br />
	if( Length > 0 )<br />
	{<br />
		Sum += *(PUCHAR)WD;<br />
	}<br />
<br />
	while( Sum >> 16 )<br />
	{<br />
		Sum = (Sum & 0xFFFF) + (Sum >> 16);<br />
	}<br />
<br />
	return (USHORT) ~Sum;<br />
}<br />
<br />
<br />
void main()<br />
{<br />
	PIP_HEADER IpHeader = (PIP_HEADER) Packet;<br />
	PTCP_HEADER TcpHeader = (PTCP_HEADER)( Packet + IpHeader->HeaderLength*4);<br />
	USHORT TcpDataLength = 	ntohs( IpHeader->TotalLength ) - IpHeader->HeaderLength*4;<br />
<br />
	DumpIPHeader( IpHeader );<br />
	DumpTCPHeader( TcpHeader );<br />
	printf( "\nTcpDataLength %d\n", TcpDataLength );<br />
<br />
	USHORT OldChecksum;<br />
<br />
	OldChecksum = IpHeader->Checksum;<br />
	IpHeader->Checksum = 0;<br />
<br />
	printf( "\nIpHeader->Checksum 0x%X\n", Checksum( (PUCHAR) IpHeader, IpHeader->HeaderLength*4) );<br />
	printf( "\nRFC IpHeader->Checksum 0x%X\n", ChecksumRFC( (PUCHAR) IpHeader, IpHeader->HeaderLength*4) );<br />
<br />
	IpHeader->Checksum = OldChecksum;<br />
<br />
	TCP_PSEUDOHEADER TcpPSHeader;<br />
<br />
	TcpPSHeader.SourceAddress = IpHeader->SourceAddress;<br />
	TcpPSHeader.DestAddress   = IpHeader->DestAddress;<br />
	TcpPSHeader.Zero          = 0;<br />
	TcpPSHeader.Protocol      = IpHeader->Protocol;<br />
	TcpPSHeader.TcpLength     = TcpDataLength;<br />
	<br />
	UCHAR tcp[ 478 + 12 ];<br />
<br />
	OldChecksum = TcpHeader->Checksum;<br />
//	TcpHeader->Checksum = 0;<br />
<br />
	memset( tcp, 0, 478 + 12 );<br />
	memcpy( &tcp[ 0 ], &TcpPSHeader, sizeof( TcpPSHeader ) );<br />
	memcpy( &tcp[ 12 ], TcpHeader, TcpDataLength );<br />
<br />
	printf( "\nTCP Checksum 0x%X\n", Checksum( tcp, 478+12 ) );<br />
	printf( "\nRFC TCP Checksum 0x%X\n", ChecksumRFC( tcp, 478+12 ) );<br />
<br />
	TcpHeader->Checksum = OldChecksum;<br />
<br />
	printf( "\n0x%X\n", (USHORT)~OldChecksum );<br />
<br />
}<br />

Re: TCP header checksum calculation

Koep30-Aug-02 1:02

Re: TCP header checksum calculation

30-Aug-02 1:02

I can't help you.
But which Packet driver do you use, i have a similar project, but not with TCP.

Marco

AIDS30-Aug-02 1:40

AIDS

30-Aug-02 1:40

I do not use any Packet driver.
I have captured the packet using Windows 2000 Network Monitor.
And I need to calculate checksums in my driver, which is NDIS intermediate driver.

Re: TCP header checksum calculation

Stephen C. Steel30-Aug-02 12:30

Stephen C. Steel

30-Aug-02 12:30

It may not be the problem, but you should be suspicous of any cross platform code using bitfields to pick out bits like this. The C standard does not define whether bitfields are allocated starting from the most or least significant bits of the variable. Different compilers may interpret this code differently!

<br />
UCHAR HeaderLength :4; // Header length in 32-bit words<br />

Some compilers will use the high nibble, others the lower nibble. Its much safer to use masks and shifts:

Either

HeaderLength = (uchar_var & 0xF0) >> 4

or

HeaderLength = (uchar_var & 0x0F)

as appropriate.

Stephen C. Steel
Kerr Vayne Systems Ltd.

Problems with CArray Updated

Koep30-Aug-02 0:50

30-Aug-02 0:50

Hi,

i believe that i have a problem to create a instance of the following object.

Declaration :
CArray <CEndPointGroup*,CEndPointGroup*> m_arEndPointGroups;

Add Pointer :
CEndPointGroup* _pEndPointGroup = NULL;
_pEndPointGroup = new CEndPointGroup(_groupname);
m_arEndPointGroups.Add(_pEndPointGroup);

At the last line i get an error. It seems that the arEndPointGroups-object is wrong allocated. What do i wrong ?

Marco

Tomasz Sowinski30-Aug-02 0:56

30-Aug-02 0:56

What kind of error it is? Compiler error? Assert at runtime? Hardware error?

Tomasz Sowinski -- http://www.shooltz.com

Free your mind and your ass will follow.

Koep30-Aug-02 1:00

30-Aug-02 1:00

It's an assert error at runtime. Pointer Access Error !

i've tried only to make an array of CEndPointsGroup-Pointer. Frown | :(

Marco

Tomasz Sowinski30-Aug-02 1:12

30-Aug-02 1:12

Have a look at call stack. Where (file/line) is ASSERT located?

Tomasz Sowinski -- http://www.shooltz.com

Free your mind and your ass will follow.

jhwurmbach30-Aug-02 3:20

jhwurmbach

30-Aug-02 3:20

Do you have looked at CPtrArray? Maybe that helps.

BTW CArray is deprecated, nonstandard and broken. You are better off using a
std::vector<CEndPointGroup*>
or even a
std::vector<boost::shared_ptr<CEndPointGroup>>

Just remember to never use std::auto_ptr in a std:: container.

Tomasz Sowinski30-Aug-02 3:21

30-Aug-02 3:21

jhwurmbach wrote:
BTW CArray is deprecated, nonstandard and broken

Nonstandard, yes. But I'd appreciate if you'd explain 'broken' and 'deprecated' part.

Tomasz Sowinski -- http://www.shooltz.com

Free your mind and your ass will follow.

jhwurmbach30-Aug-02 3:48

jhwurmbach

30-Aug-02 3:48

Broken:
http://www.codeproject.com/cpp/ocarray.asp[^]
or
http://www.codeproject.com/cpp/carray_pitfall.asp[^]
The use of 'pitfall' is the same as MS using 'issue': Politically correct term for 'ERROR'
Meaning: CArray and references don't work.

Deprecated:
CArray is what MS had to come up with when the STL was not working, but they needed the functionality for MFC. Since the time the standard was released, there is no need to use these old nostandard CArray.

Problems with CArray

Koep30-Aug-02 0:48