今天在看sheepdog的时候发现了getifaddrs（）这个接口，它可以查找到系统所有的网络接口的信息，包括以太网卡接口和回环接口等。利用这个接口来获取本机的IP地址真是太方便了，原来的getaddrinfo()、ioctl()或者利用套接字方法等来获取IP地址的方法都没法跟这个接口比，不仅方便，而且也非常的强大，完全不需要绑定主机名等类似的操作。看了一下glibc的源码，它是利用netlink来实现的，所以在使用这个接口的时候一定要确保你的内核支持netlink。下面是man手册中的一个例子：
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <ifaddrs.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
struct ifaddrs *ifaddr, *ifa;
int family, s;
char host[NI_MAXHOST];
if (getifaddrs(&ifaddr) == -1) {
perror("getifaddrs");
exit(EXIT_FAILURE);
}
/* Walk through linked list, maintaining head pointer so we
* can free list later */
for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
if (ifa->ifa_addr == NULL)
continue;
family = ifa->ifa_addr->sa_family;
/* Display interface name and family (including symbolic
* form of the latter for the common families) */
printf("%s address family: %d%s\n",
ifa->ifa_name, family,
(family == AF_PACKET) ? " (AF_PACKET)" :
(family == AF_INET) ? " (AF_INET)" :
(family == AF_INET6) ? " (AF_INET6)" : "");
/* For an AF_INET* interface address, display the address */
if (family == AF_INET || family == AF_INET6) {
s = getnameinfo(ifa->ifa_addr,
(family == AF_INET) ? sizeof(struct sockaddr_in) :
sizeof(struct sockaddr_in6),
host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
if (s != 0) {
printf("getnameinfo() failed: %s\n", gai_strerror(s));
exit(EXIT_FAILURE);
}
printf("\taddress: <%s>\n", host);
}
}
freeifaddrs(ifaddr);
exit(EXIT_SUCCESS);
}