create c programm for insert rules in netfilters

[Fallucchi Antonio <fallucch@cisbic.com>]

hi,

I must create a c programm for inserting rules in iptables..

I have used  "do_command" function:

char *tablename = "filter";
iptc_handle_t h = NULL;
char *vettarg[] = {"iptable", "-t", "nat", "-A", "OUTPUT", "-d", "!", 
"127.0.0.1", "-p", "tcp", "--tcp-flags", "syn", "syn", "-j", "QUEUE"};
int numarg=15;
do_command(numarg, vettarg, &tablename, &h);


but, the program crashes with segmentation fault doing;

for (protocol = argv[optind-1]; *protocol; protocol++)
                *protocol = tolower(*protocol);

please help me!
Antonio