struct netent *getnetent(void);
struct netent *getnetbyname(const char *name);
struct netent *getnetbyaddr(uint32_t net, int type);
void setnetent(int stayopen);
void endnetent(void);
/* Description of data base entry for a single network. NOTE: here a
poor assumption is made. The network number is expected to fit
into an unsigned long int variable. */
struct netent
{
char *n_name; /* Official name of network. */
char **n_aliases; /* Alias list. */
int n_addrtype; /* Net address type. */
uint32_t n_net; /* Network number. */
};
注意：
(1) netent.n_net 是主机字节序，跟 hostent 有所不同
(2) 原理：ubuntu 下是读取 /etc/networks 文件（见man getnetent）
/**
* getnetent()
* OS: Ubuntu 11.04 Server
*/
#include <stdio.h>
#include <netdb.h>
static void printnet(struct netent *net);
int main()
{
struct netent *net = NULL;
setnetent(1);
while( (net = getnetent()) != NULL )
{
printnet(net);
printf("\n");
}
endnetent();
return 0;
}
static void printnet(struct netent *net)
{
char **p = NULL;
printf("name of network: %s\n", net->n_name);
for(p = net->n_aliases; *p; p++)
{
printf("alias: %s\n", *p);
}
if(net->n_addrtype == AF_INET)
{
printf("address type: AF_INET\n");
}
else
{
printf("adress type: not IPv4 address\n");
}
printf("network number: %x\n", net->n_net);
}
/*
output:
name of network: link-local
address type: AF_INET
network number: a9fe0000
/etc/networks:
# symbolic names for networks, see networks(5) for more information
link-local 169.254.0.0
*/
