Linux C 网络编程
获取本地 ip 地址，mac，通过域名获取对应的 ip，是网络编程可能遇到的比较常见的操作了，所以总结如下（封装了3个函数），
直接上代码：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <netdb.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/socket.h>
#define MAC_SIZE 18
#define IP_SIZE 16
// function declare
int get_ip_by_domain(const char *domain, char *ip); // 根据域名获取ip
int get_local_mac(const char *eth_inf, char *mac); // 获取本机mac
int get_local_ip(const char *eth_inf, char *ip); // 获取本机ip
/****** main test **********/
int main(void)
{
char ip;
char mac;
const char *test_domain = "www.baidu.com";
const char *test_eth = "eth0";
get_ip_by_domain(test_domain, ip);
printf("%s ip: %s\n", test_domain, ip);
get_local_mac(test_eth, mac);
printf("local %s mac: %s\n", test_eth, mac);
get_local_ip(test_eth, ip);
printf("local %s ip: %s\n", test_eth, ip);
return 0;
}
// 根据域名获取ip
int get_ip_by_domain(const char *domain, char *ip)
{
char **pptr;
struct hostent *hptr;
hptr = gethostbyname(domain);
if(NULL == hptr)
{
printf("gethostbyname error for host:%s/n", domain);
return -1;
}
for(pptr = hptr->h_addr_list ; *pptr != NULL; pptr++)
{
if (NULL != inet_ntop(hptr->h_addrtype, *pptr, ip, IP_SIZE) )
{
return 0; // 只获取第一个 ip
}
}
return -1;
}
// 获取本机mac
int get_local_mac(const char *eth_inf, char *mac)
{
struct ifreq ifr;
int sd;
bzero(&ifr, sizeof(struct ifreq));
if( (sd = socket(AF_INET, SOCK_STREAM, 0)) < 0)
{
printf("get %s mac address socket creat error\n", eth_inf);
return -1;
}
strncpy(ifr.ifr_name, eth_inf, sizeof(ifr.ifr_name) - 1);
if(ioctl(sd, SIOCGIFHWADDR, &ifr) < 0)
{
printf("get %s mac address error\n", eth_inf);
close(sd);
return -1;
}
snprintf(mac, MAC_SIZE, "%02x:%02x:%02x:%02x:%02x:%02x",
(unsigned char)ifr.ifr_hwaddr.sa_data,
(unsigned char)ifr.ifr_hwaddr.sa_data,
(unsigned char)ifr.ifr_hwaddr.sa_data,
(unsigned char)ifr.ifr_hwaddr.sa_data,
(unsigned char)ifr.ifr_hwaddr.sa_data,
(unsigned char)ifr.ifr_hwaddr.sa_data);
close(sd);
return 0;
}
// 获取本机ip
int get_local_ip(const char *eth_inf, char *ip)
{
int sd;
struct sockaddr_in sin;
struct ifreq ifr;
sd = socket(AF_INET, SOCK_DGRAM, 0);
if (-1 == sd)
{
printf("socket error: %s\n", strerror(errno));
return -1;
}
strncpy(ifr.ifr_name, eth_inf, IFNAMSIZ);
ifr.ifr_name = 0;
// if error: No such device
if (ioctl(sd, SIOCGIFADDR, &ifr) < 0)
{
printf("ioctl error: %s\n", strerror(errno));
close(sd);
return -1;
}
memcpy(&sin, &ifr.ifr_addr, sizeof(sin));
snprintf(ip, IP_SIZE, "%s", inet_ntoa(sin.sin_addr));
close(sd);
return 0;
}
测试运行
结果如下：
ifreq 结构体分析和使用:
struct ifreq
{
#define IFHWADDRLEN 6
union
{
char ifrn_name;
} ifr_ifrn;
union {
struct sockaddr ifru_addr;
struct sockaddr ifru_dstaddr;
struct sockaddr ifru_broadaddr;
struct sockaddr ifru_netmask;
structsockaddr ifru_hwaddr;
short ifru_flags;
int ifru_ivalue;
int ifru_mtu;
structifmap ifru_map;
char ifru_slave;
char ifru_newname;
void __user * ifru_data;
struct if_settings ifru_settings;
} ifr_ifru;
};
#define ifr_name ifr_ifrn.ifrn_name
#define ifr_hwaddr ifr_ifru.ifru_hwaddr
#define ifr_addr ifr_ifru.ifru_addr
#define ifr_dstaddr ifr_ifru.ifru_dstaddr
#define ifr_broadaddr ifr_ifru.ifru_broadaddr
#define ifr_netmask ifr_ifru.ifru_netmask
#define ifr_flags ifr_ifru.ifru_flags
#define ifr_metric ifr_ifru.ifru_ivalue
#define ifr_mtuifr_ifru.ifru_mtu
#define ifr_mapifr_ifru.ifru_map
#define ifr_slave ifr_ifru.ifru_slave
#define ifr_data ifr_ifru.ifru_data
#define ifr_ifindex ifr_ifru.ifru_ivalue
#define ifr_bandwidth ifr_ifru.ifru_ivalue
#define ifr_qlen ifr_ifru.ifru_ivalue
#define ifr_newname ifr_ifru.ifru_newname
#define ifr_settings ifr_ifru.ifru_settings
基本介绍:
ifreq结构定义在/usr/include/net/if.h，用来配置ip地址，激活接口，配置MTU等接口信息的。其中包含了一个接口的名 字和具体内容——（是个共用体，有可能是IP地址，广播地址，子网掩码，MAC号，MTU或其他内容）。ifreq包含在ifconf结构中。而 ifconf结构通常是用来保存所有接口的信息的。
举例说明：
在Linux系统中，ifconfig命令是通过ioctl接口与内核通信，例如，当系统管理员输入如下命令来改变接口eth0的MTU大小：
ifconfig eth0 mtu 1250
ifconfig命令首先打开一个socket，然后通过系统管理员输入的参数初始化一个数据结构，并通过ioctl调用将数据传送到内核。SIOCSIFMTU是命令标识符。
struct ifreq data;
fd = socket(PF_INET, SOCK_DGRAM, 0);
< ... initialize "data" ...>
err = ioctl(fd, SIOCSIFMTU, &data);
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