tcpdump_获取数据链路层类型

#include <pcap.h>#include <stdio.h>#include <stdlib.h>/* * 获取数据链路层类型 */ /* * pcap_lookupdev介绍 *NAME pcap_lookupdev - find the default device on which to captureSYNOPSIS #include <pcap/pcap.h> char errbuf[PCAP_ERRBUF_SIZE]; char *pcap_lookupdev(char *errbuf);DESCRIPTION pcap_lookupdev() returns a pointer to a string giving the name of a network device suitable for use with pcap_create() and pcap_activate(), or with pcap_open_live(), and with pcap_lookupnet().If there is an error, NULL is returned and errbuf is filled in with an appropriate error message. errbuf is assumed to be able tohold at least PCAP_ERRBUF_SIZE chars.*//* * pcap_open_live介绍 *NAME pcap_open_live - open a device for capturingSYNOPSIS #include <pcap/pcap.h> char errbuf[PCAP_ERRBUF_SIZE]; pcap_t *pcap_open_live(const char *device, int snaplen, int promisc, int to_ms, char *errbuf);DESCRIPTION pcap_open_live() is used to obtain a packet capture handle to look at packets on the network.device is a string that specifies the network device to open; on Linux systems with 2.2 or later kernels, a device argument of "any" or NULL can be used to capture packets from all interfaces. snaplen specifies the snapshot length to be set on the handle. promisc specifies if the interface is to be put into promiscuous mode. to_ms specifies the read timeout in milliseconds.RETURN VALUE pcap_open_live() returns a pcap_t * on success and NULL on failure. If NULL is returned, errbuf is filled in with an appropriate error mes- sage. errbuf may also be set to warning text when pcap_open_live() succeds; to detect this case the caller should storea zero-length string in errbuf before calling pcap_open_live() and display the warn- ing to the user if errbuf is no longer a zero-length string. errbuf is assumed to be able to hold at least PCAP_ERRBUF_SIZE chars.*//* * pcap_datalink介绍 *NAME pcap_datalink - get the link-layer header typeSYNOPSIS #include <pcap/pcap.h> int pcap_datalink(pcap_t *p);DESCRIPTION pcap_datalink()returns the link layer type for the live capture or ``savefile'' specified by p.*/#define DEFAULT_SNAPLEN 68 intmain (int argc, char **argv){char errbuf[PCAP_ERRBUF_SIZE];char *netdev = pcap_lookupdev(errbuf);if(netdev == NULL){printf("error:%s/n",errbuf);exit(1);}pcap_t *pd = pcap_open_live(netdev, DEFAULT_SNAPLEN, 0, 1000, errbuf);if(pd == NULL){printf("error:%s/n",errbuf);exit(1);}int type = pcap_datalink(pd);printf("type:%d/n",type);// 返回值的意思请查阅:http://www.unix.com/man-page/All/7/pcap-linktype/pcap_close(pd);return 0;}