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[IP_SIZE];  
    char mac[MAC_SIZE];  
    const char *test_domain = "www.baidu.com";  
    const char *test_eth = "eth0";  
  
    get_ip_by_domain(test_domain, ip);  
    printf("%s ip: %s
", test_domain, ip);  
  
    get_local_mac(test_eth, mac);  
    printf("local %s mac: %s
", test_eth, mac);  
  
    get_local_ip(test_eth, ip);  
    printf("local %s ip: %s
", 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
", 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
", eth_inf);  
        close(sd);  
        return -1;  
    }  
  
    snprintf(mac, MAC_SIZE, "%02x:%02x:%02x:%02x:%02x:%02x",  
        (unsigned char)ifr.ifr_hwaddr.sa_data[0],   
        (unsigned char)ifr.ifr_hwaddr.sa_data[1],  
        (unsigned char)ifr.ifr_hwaddr.sa_data[2],   
        (unsigned char)ifr.ifr_hwaddr.sa_data[3],  
        (unsigned char)ifr.ifr_hwaddr.sa_data[4],  
        (unsigned char)ifr.ifr_hwaddr.sa_data[5]);  
  
    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
", strerror(errno));  
        return -1;        
    }  
  
    strncpy(ifr.ifr_name, eth_inf, IFNAMSIZ);  
    ifr.ifr_name[IFNAMSIZ - 1] = 0;  
      
    // if error: No such device  
    if (ioctl(sd, SIOCGIFADDR, &ifr) < 0)  
    {  
        printf("ioctl error: %s
", 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[IFNAMSIZ];  
 } ifr_ifrn;
 
 union {
  struct sockaddr ifru_addr;
  struct sockaddr ifru_dstaddr;
  struct sockaddr ifru_broadaddr;
  struct sockaddr ifru_netmask;
  struct  sockaddr ifru_hwaddr;
  short ifru_flags;
  int ifru_ivalue;
  int ifru_mtu;
  struct  ifmap ifru_map;
  char ifru_slave[IFNAMSIZ]; 
  char ifru_newname[IFNAMSIZ];
  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_mtu  ifr_ifru.ifru_mtu 
#define ifr_map  ifr_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);