address@hidden:~/devel$ gcc --version
gcc (Ubuntu/Linaro 4.5.2-8ubuntu4) 4.5.2
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
address@hidden:~/devel$ gcc -std=gnu99 -o kk kk.c
address@hidden:~/devel$ ./kk
while my_iphdr is 20 bytes long
my_iphdr: the first byte: 0x45
          tos      is as offset 1
          tot_len  is as offset 2
          id       is as offset 4
          frag_off is as offset 6
          ttl      is as offset 8
          protocol is as offset 9
          check    is as offset 10
          saddr    is as offset 12
          daddr    is as offset 16

45 01 00 02 00 03 00 04 
05 06 00 07 00 00 00 08 
00 00 00 09 

the iphdr is 20 bytes long
iphdr:    the first byte: 0x45
          tos      is as offset 1
          tot_len  is as offset 2
          id       is as offset 4
          frag_off is as offset 6
          ttl      is as offset 8
          protocol is as offset 9
          check    is as offset 10
          saddr    is as offset 12
          daddr    is as offset 16

45 01 00 02 00 03 00 04 
05 06 00 07 00 00 00 08 
00 00 00 09 

address@hidden:~/devel$ tcc -run kk.c
while my_iphdr is 20 bytes long
my_iphdr: the first byte: 0x45
          tos      is as offset 1
          tot_len  is as offset 2
          id       is as offset 4
          frag_off is as offset 6
          ttl      is as offset 8
          protocol is as offset 9
          check    is as offset 10
          saddr    is as offset 12
          daddr    is as offset 16

45 01 00 02 00 03 00 04 
05 06 00 07 00 00 00 08 
00 00 00 09 

the iphdr is 24 bytes long
iphdr:    the first byte: 0x45
          tos      is as offset 4
          tot_len  is as offset 6
          id       is as offset 8
          frag_off is as offset 10
          ttl      is as offset 12
          protocol is as offset 13
          check    is as offset 14
          saddr    is as offset 16
          daddr    is as offset 20

45 76 9a 08 01 21 00 02 
00 03 00 04 05 06 00 07 
00 00 00 08 00 00 00 09 

address@hidden:~/devel$ apt-show-versions | grep tinycc
tinycc 110318git-1 installed: No available version in archive