在linux下使用ifconfigl命令能很方便的查看网卡与网线是否连通，运行ifconfig eth0命令大致输出如下：

# ifconfig eth0

eth0 Link encap:Ethernet HWaddr 00:25:35:68:CC:D6

inet addr:192.168.1.168 Bcast:192.168.1.255 Mask:255.255.255.0

inet6 addr: fe80::215:c5ff:fe18:ccd6/64 Scope:Link

UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1

RX packets:130722 errors:0 dropped:0 overruns:0 frame:0

TX packets:112560 errors:0 dropped:0 overruns:0 carrier:0

collisions:0 txqueuelen:1000

RX bytes:104371099 (99.5 MiB) TX bytes:20518584 (19.5 MiB)

Interrupt:16

其中的RUNNING就表示网卡与网线正常链接，拔掉网线再运行此命令就会发现RUNNING不在了。我的目的是用C语言来实现程序，而linux系统提供了popen/pclose进程管道让C和shell很方便的交互，不过使用的时候要注意设置权限，以免造成安全隐患。废话不多说，看下面C代码结合shell命令检测网卡与网线连通状况：netstat.c

#include

#include

#include

#include

/**********************************************************************

* 函数名称： GetNetStat

* 功能描述： 检测网络链接是否断开

* 输入参数：

* 输出参数： 无

* 返 回 值： 正常链接1,断开返回-1

* 其它说明： 本程序需要超级用户权限才能成功调用ifconfig命令

* 修改日期 版本号 修改人 修改内容

* ---------------------------------------------------------------------

* 2010/04/02 V1.0 eden_mgqw

***********************************************************************/

int GetNetStat( )

{

char buffer[BUFSIZ];

FILE *read_fp;

int chars_read;

int ret;

memset( buffer, 0, BUFSIZ );

read_fp = popen("ifconfig eth0 | grep RUNNING", "r");

if ( read_fp != NULL )

{

chars_read = fread(buffer, sizeof(char), BUFSIZ-1, read_fp);

if (chars_read > 0)

{

ret = 1;

}

else

{

ret = -1;

}

pclose(read_fp);

}

else

{

ret = -1;

}

return ret;

}

int main()

{

int i=0;

i = GetNetStat();

printf( "\nNetStat = %d\n", i );

return 0;

}

下面是编译运行程序的输出结果(正常返回1，断开返回-1)：# cc netstat.c# ./a.outNetStat = 1

C语言实现：

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

#include

static void die(const char *s)

{

fprintf(stderr,"error: %s (%s)\n", s, strerror(errno));

exit(-1);

}

static void setflags(int s, struct ifreq *ifr, int set, int clr)

{

if(ioctl(s, SIOCGIFFLAGS, ifr) < 0) die("SIOCGIFFLAGS");

ifr->ifr_flags = (ifr->ifr_flags & (~clr)) | set;

if(ioctl(s, SIOCSIFFLAGS, ifr) < 0) die("SIOCSIFFLAGS");

}

static inline void init_sockaddr_in(struct sockaddr_in *sin, const char *addr)

{

sin->sin_family = AF_INET;

sin->sin_port = 0;

sin->sin_addr.s_addr = inet_addr(addr);

}

static void setmtu(int s, struct ifreq *ifr, const char *mtu)

{

int m = atoi(mtu);

ifr->ifr_mtu = m;

if(ioctl(s, SIOCSIFMTU, ifr) < 0) die("SIOCSIFMTU");

}

static void setdstaddr(int s, struct ifreq *ifr, const char *addr)

{

init_sockaddr_in((struct sockaddr_in *) &ifr->ifr_dstaddr, addr);

if(ioctl(s, SIOCSIFDSTADDR, ifr) < 0) die("SIOCSIFDSTADDR");

}

static void setnetmask(int s, struct ifreq *ifr, const char *addr)

{

init_sockaddr_in((struct sockaddr_in *) &ifr->ifr_netmask, addr);

if(ioctl(s, SIOCSIFNETMASK, ifr) < 0) die("SIOCSIFNETMASK");

}

static void setaddr(int s, struct ifreq *ifr, const char *addr)

{

init_sockaddr_in((struct sockaddr_in *) &ifr->ifr_addr, addr);

if(ioctl(s, SIOCSIFADDR, ifr) < 0) die("SIOCSIFADDR");

}

int main(int argc, char *argv[])

{

struct ifreq ifr;

int s;

unsigned int addr, mask, flags;

char astring[20];

char mstring[20];

char *updown, *brdcst, *loopbk, *ppp, *running, *multi;

argc--;

argv++;

if(argc == 0) return 0;

memset(&ifr, 0, sizeof(struct ifreq));

strncpy(ifr.ifr_name, argv[0], IFNAMSIZ);

ifr.ifr_name[IFNAMSIZ-1] = 0;

argc--, argv++;

if((s = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {

die("cannot open control socket\n");

}

if (argc == 0) {

if (ioctl(s, SIOCGIFADDR, &ifr) < 0) {

perror(ifr.ifr_name);

return -1;

} else

addr = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr.s_addr;

if (ioctl(s, SIOCGIFNETMASK, &ifr) < 0) {

perror(ifr.ifr_name);

return -1;

} else

mask = ((struct sockaddr_in *)&ifr.ifr_addr)->sin_addr.s_addr;

if (ioctl(s, SIOCGIFFLAGS, &ifr) < 0) {

perror(ifr.ifr_name);

return -1;

} else

flags = ifr.ifr_flags;

sprintf(astring, "%d.%d.%d.%d",

addr & 0xff,

((addr >> 8) & 0xff),

((addr >> 16) & 0xff),

((addr >> 24) & 0xff));

sprintf(mstring, "%d.%d.%d.%d",

mask & 0xff,

((mask >> 8) & 0xff),

((mask >> 16) & 0xff),

((mask >> 24) & 0xff));

printf("%s: ip %s mask %s flags [", ifr.ifr_name,

astring,

mstring

);

updown = (flags & IFF_UP) ? "up" : "down";

brdcst = (flags & IFF_BROADCAST) ? " broadcast" : "";

loopbk = (flags & IFF_LOOPBACK) ? " loopback" : "";

ppp = (flags & IFF_POINTOPOINT) ? " point-to-point" : "";

running = (flags & IFF_RUNNING) ? " running" : "";

multi = (flags & IFF_MULTICAST) ? " multicast" : "";

printf("%s%s%s%s%s%s]\n", updown, brdcst, loopbk, ppp, running, multi);

return 0;

}

while(argc > 0) {

if (!strcmp(argv[0], "up")) {

setflags(s, &ifr, IFF_UP, 0);

} else if (!strcmp(argv[0], "mtu")) {

argc--, argv++;

if (!argc) {

errno = EINVAL;

die("expecting a value for parameter \"mtu\"");

}

setmtu(s, &ifr, argv[0]);

} else if (!strcmp(argv[0], "-pointopoint")) {

setflags(s, &ifr, IFF_POINTOPOINT, 1);

} else if (!strcmp(argv[0], "pointopoint")) {

argc--, argv++;

if (!argc) {

errno = EINVAL;

die("expecting an IP address for parameter \"pointtopoint\"");

}

setdstaddr(s, &ifr, argv[0]);

setflags(s, &ifr, IFF_POINTOPOINT, 0);

} else if (!strcmp(argv[0], "down")) {

setflags(s, &ifr, 0, IFF_UP);

} else if (!strcmp(argv[0], "netmask")) {

argc--, argv++;

if (!argc) {

errno = EINVAL;

die("expecting an IP address for parameter \"netmask\"");

}

setnetmask(s, &ifr, argv[0]);

} else if (isdigit(argv[0][0])) {

setaddr(s, &ifr, argv[0]);

setflags(s, &ifr, IFF_UP, 0);

}

argc--, argv++;

}

return 0;

}