Function To Return A Value

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2.00/5 (3 votes)

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How do I get this function to return a value of 1 or 0 so that I can reference it elsewhere? Thank you.

void end_packet(char *_packet)
{
TCPHEADER *tcp_header = (TCPHEADER *)_packet;
BYTE flags = ( ntohs(tcp_header->info_ctrl) & 0x003F );
int EP;
	if ( flags & 0x01 && flags & 0x10 )
		{
		EP = 1; //End
		}
	else
	{
		EP = 0; //Not End
	}
}

Posted 18-Sep-11 16:12pm

Member 7766180

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Sergey Alexandrovich Kryukov 18-Sep-11 22:37pm

What's the problem? What this function is supposed to do?! (Don't answer "to return 0 or 1" -- it's obvious.)
--SA

Albert Holguin 19-Sep-11 15:32pm

I deleted messages that are not related to question asked.

2 solutions

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Sergey Alexandrovich Kryukov · Accepted Answer · 2011-09-18T16:40:00

Solution 1

Please see my comment to the question.

How can you ask this question and declare a void function?! Make a return type, say, byte and return EP — if this type. Better yet, introduce enum type with values of 0 and 1 and return it. Is that was your problem?

—SA

Posted 18-Sep-11 16:40pm

Sergey Alexandrovich Kryukov

Updated 18-Sep-11 16:41pm

v2

Comments

Member 7766180 18-Sep-11 22:50pm

How can I make a return type of byte and return EP? As you know I'm new to this and this would be a tremondous help if you would show me. I learn by visual example. Thank you kind sir. How can I call or grab this value in another part of the code? Here is the whole funcion.

void decode_tcp(char *_packet)
{
TCPHEADER *tcp_header = (TCPHEADER *)_packet;
BYTE flags = ( ntohs(tcp_header->info_ctrl) & 0x003F );
int EP;
printf("\n Source Port : %ld", htons(tcp_header->source_port));
printf("\n Destination Port : %ld", htons(tcp_header->destination_port));
printf("\n Control Bits : ");

if ( flags & 0x01 ) // FIN
printf( "FIN " );
if ( flags & 0x02 ) // SYN
printf( "SYN " );
if ( flags & 0x04 ) // RST
printf( "RST " );
if ( flags & 0x08 ) // PSH
printf( "PSH " );
if ( flags & 0x10 ) // ACK
printf( "ACK " );
if ( flags & 0x20 ) // URG
printf( "URG " );
printf("\n Sequence Number : %lu", ntohl(tcp_header->seq_number));
if ( flags & 0x01 && flags & 0x10 )
{
printf("\n End of Packet " );
EP = 1;
}
else
printf("\n Not End of Packet " );
EP = 0;
}

Sergey Alexandrovich Kryukov 19-Sep-11 14:38pm

Replace void decode_tcp with int decode_tcp and add return EP; at the very end. Optionally, replace int EP with byte VP or, better yet, with some enum type you declare before the function.
I can see really bad style here. You want to calculate something and you also print something. Avoid printing in any function having any logic, unless this is temporary, just for development. Also you are commenting something which should be a part of code.

Instead of writing

if (flags % 0x04)
   ...

write

if (flags & RST)
   ...

Declare enum TcpFlags { FIN = 1, SYN = 2, RST = 4, /* etc... */ }

You should get rid of all immediate constants hard-coded in the code; having them makes in non-supportable. Declare all constants explicitly; enum is one of the best ways to do it.

If you say you always learn be visual example, be warned: you learn next to nothing due to missing other important ways to learn.

Good luck,
--SA

Member 7766180 19-Sep-11 15:12pm

Thank you so very much! I appreciate you taking the time to show me how it's done. Good luck to you also!

Sergey Alexandrovich Kryukov 19-Sep-11 15:29pm

Hope it can help you.
Cheers!
--SA

Manfred Rudolf Bihy 21-Sep-11 4:09am

Great follow up! 5+

Sergey Alexandrovich Kryukov 21-Sep-11 9:41am

Thank you, Manfred.
--SA

Stefan_Lang · Accepted Answer · 2011-09-20T21:56:00

Solution 3

You might want to read up on how to use functions in the C or C++ language Check out Functions at www.cplusplus.com. Or better yet, go for the Tutorial there.

It will take you a lot less time understanding the principles of C++ programming that way than trying to figure out the workings of the language by example alone. the difference will be about the same as the time an archeologist would take to decipher an unknown language as opposed to one using a dictionary!

Posted 20-Sep-11 21:56pm

Stefan_Lang

Comments

Member 7766180 21-Sep-11 4:05am

Thank you! Im finding it a little difficult as I come from VB and VBA and its sometimes hard to leave that headspace and go into a very different one. I appreciate your syggestion and the reference! Thank you!

Stefan_Lang 21-Sep-11 4:19am

I understand. VB/VBA may not have been the best way to get started with programming - the 'B' (for Basic) isn't in that name for nothing! But since you can hardly change that now, asking and reading up on the concpets you're not familiar with is the second best thing.

FYI I upvoted for question to balance the downvotes - for all it's simplicity you were right to ask, and you asked in the right forum as well.

Member 7766180 21-Sep-11 6:45am

Thank you!