netinet/tcp.h -- tcphdr structure compile error

Hi experts.

I've written a program to send tcp/ip packets using raw sockets on unix. I've got rid of all the compile errors, except for one remaining problem.

First of all, here are the libraries I've included:

# include <stdio.h>
# include <string.h>
# include <sys/types.h>
# include <sys/socket.h>
# include <netinet/in.h>
# include <netinet/ip.h>
# include <netinet/tcp.h>

My code just basically creates one big buffer and points "ip" and "tcphdr" structures within this buffer. I then fill out all the values and attempt to fire off the packet.

All my remaining compile errors relate to tcphdr... I've looked at /usr/include/tcp.h and cannot make any sense of this at all. The tcphdr structure DOES have the members it is complaining about and they are spelt correctly!

net.c: In function ‘SEND’:
net.c:41: error: ‘struct tcphdr’ has no member named ‘th_sport’
net.c:42: error: ‘struct tcphdr’ has no member named ‘th_dport’
net.c:43: error: ‘struct tcphdr’ has no member named ‘th_seq’
net.c:44: error: ‘struct tcphdr’ has no member named ‘th_ack’
net.c:45: error: ‘struct tcphdr’ has no member named ‘th_x2’
net.c:46: error: ‘struct tcphdr’ has no member named ‘th_off’
net.c:47: error: ‘struct tcphdr’ has no member named ‘th_flags’
net.c:47: error: ‘TH_SYN’ undeclared (first use in this function)
net.c:47: error: (Each undeclared identifier is reported only once
net.c:47: error: for each function it appears in.)
net.c:48: error: ‘struct tcphdr’ has no member named ‘th_win’
net.c:49: error: ‘struct tcphdr’ has no member named ‘th_sum’
net.c:50: error: ‘struct tcphdr’ has no member named ‘th_urp’

I created an instance of the tcphdr structure like this:

struct tcphdr * tcph = ( struct tcphdr * ) datagram + sizeof ( struct ip ) ;

And I was setting the members like follows:

tcph->th_dport = htons ( port ) ;

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bpmurrayConnect With a Mentor Commented:
I think I found it. Try this:

      gcc -D_BSD_SOURCE net.c -o net
Sound like you may be including another definition of tcphdr which prevents the one in netinet/tcp.h being seen. Check the -I dirs to make sure you're grabbing the right version.
suma_dsAuthor Commented:
hey thanks for the responce.

i'm new to unix and as such, not quite sure how to do what you're asking. is that a bash command or something to do with gcc?

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It's to do with gcc. What is your compile command-line?

BTW, what operating system are you doing this on ? Windows? Linux? Some other Unix?
suma_dsAuthor Commented:
I'm just using  "gcc net.c -o net.exe"  to compile it.

I tried  "gcc -net.c -I dirs -o net.exe"  but that didnt seem to do anything different.

I'm running Linux...
suma_dsAuthor Commented:
I also tried it on a completely different box -- running a different distro of linux. Same problem.
change your compile line to:

    gcc -D__FAVOR_BSD net.c -o net

Just wondering - why call the executable "net.exe" since .exe is Windows only?
suma_dsAuthor Commented:
no joy... i'm still getting the same tcphdr errors.

as for the exe thing, i've just recently migrated from windows.. and although i really do prefer linux,  life without the win32 api is a pretty big change.... so i guess i just call it exe to make it feel more like home :)

btw if it would help at all i could post the complete code of net.c... let me know.

OK - if you posted the code, it might help. This machine has Windows, but has cygwin, so I should be able to approximate the linux environment.
Just checked ...

If I use gcc 4.0.2 something similar to your code compiles fine, but gcc 3.4.6 fails with the same error you're getting. I looked at the code, and the include files are quite different, although the comments indicate that they're both BSD v8.1. I think it has got to be some -D flag to get it to do the right thing.

I also have another toolchain installed for my GP2X, and that's got the naughty version too, even though this is 4.0.2 too. Hmmmmm! I'll continue to hack ....
suma_dsAuthor Commented:
sweet! it works no problem.

many thanks.
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