pcap_open_live.3pcap man page
pcap_open_live — open a device for capturing
#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);
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.
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 message. errbuf may also be set to warning text when pcap_open_live() succeeds; to detect this case the caller should store a zero-length string in errbuf before calling pcap_open_live() and display the warning 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(3PCAP), pcap_create(3PCAP), pcap_activate(3PCAP)