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#include <stdio.h>
#define IPSTRLEN 20
int
ip_str_to_ip_tuple(char ip_str[], int ip_tuple[])
{
int retval;
if (4!=(retval=sscanf(ip_str, "%d.%d.%d.%d",
&ip_tuple[0], &ip_tuple[1], &ip_tuple[2], &ip_tuple[3]))) {
fprintf(stderr, "Error: sscanf failed, retval was: %d\n", retval);
return retval;
}
return 0;
}
int
ip_tuple_to_ip_str(int ip_tuple[], char ip_str[], int ip_str_size)
{
int retval;
if (IPSTRLEN<(retval=snprintf(ip_str, ip_str_size, "%d.%d.%d.%d",
ip_tuple[3], ip_tuple[2], ip_tuple[1], ip_tuple[0]))) {
return retval;
}
return 0;
}
unsigned long
ip_tuple_to_addr(int ip_tuple[])
{
unsigned long result=0;
for (int i = 0; i < 4; i += 1) {
result = result<<8;
result = ip_tuple[i]|result;
}
return result;
}
int
addr_to_ip_tuple(unsigned long addr, int ip_tuple[])
{
for (int i = 0; i < 4; i += 1) {
ip_tuple[i] = (addr>>i*8)&255;
}
return 0;
}
unsigned long
compute_netmask_for_size(int net_size)
{
unsigned long netmask = 0xffffffff;
netmask = netmask<<net_size;
return netmask;
}
unsigned long
compute_network_address(unsigned long host_addr, unsigned long netmask)
{
unsigned long net_addr;
net_addr = host_addr&netmask;
return net_addr;
}
unsigned long
computer_router_address(unsigned long host_addr, unsigned long netmask)
{
unsigned long router_addr;
router_addr = compute_network_address(host_addr, netmask)+1;
return router_addr;
}
int
addr_to_ip_str(unsigned long addr, char ip_str[], int ip_str_size)
{
int ip_tuple[4];
addr_to_ip_tuple(addr, ip_tuple);
if (ip_tuple_to_ip_str(ip_tuple, ip_str, ip_str_size)) {
fprintf(stderr, "Error: IP Address malformed.\n");
}
return 0;
}
int
main(void)
{
char the_ip[]="147.142.207.19", new_ip[IPSTRLEN];
int net_size=8;
int ip_tuple[4];
unsigned long ip_addr;
if (ip_str_to_ip_tuple(the_ip, ip_tuple)) {
fprintf(stderr, "Invalid IP address: %s\n", the_ip);
return 1;
}
ip_addr = ip_tuple_to_addr(ip_tuple);
printf("IP Address: %lx\n", ip_addr);
if (addr_to_ip_str(compute_network_address(ip_addr,
compute_netmask_for_size(net_size)), new_ip, IPSTRLEN)) {
fprintf(stderr, "Couldn't format network address.\n");
return 1;
}
printf("Network for this host (netmask %lx): %s\n",
compute_netmask_for_size(net_size), new_ip);
if (addr_to_ip_str(computer_router_address(ip_addr,
compute_netmask_for_size(net_size)), new_ip, IPSTRLEN)) {
fprintf(stderr, "Couldn't format router address.\n");
return 1;
}
printf("Probable router for this host (netmask %lx): %s\n",
compute_netmask_for_size(net_size), new_ip);
return 0;
}
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