PCAP_DATALINK(3)       FreeBSD Library Functions Manual       PCAP_DATALINK(3)

NAME
       pcap_datalink - get the link-layer header type

SYNOPSIS
       #include <pcap/pcap.h>

       int pcap_datalink(pcap_t *p);

DESCRIPTION
       pcap_datalink() returns the link-layer header type for the live capture
       or ``savefile'' specified by p.

       It must not be called on a pcap descriptor created by pcap_create(3)
       that has not yet been activated by pcap_activate(3).

       https://www.tcpdump.org/linktypes.html lists the values pcap_datalink()
       can return and describes the packet formats that correspond to those
       values.

       Do NOT assume that the packets for a given capture or ``savefile`` will
       have any given link-layer header type, such as DLT_EN10MB for Ethernet.
       For example, the "any" device on Linux will have a link-layer header
       type of DLT_LINUX_SLL even if all devices on the system at the time the
       "any" device is opened have some other data link type, such as
       DLT_EN10MB for Ethernet.

RETURN VALUE
       pcap_datalink() returns the link-layer header type on success and
       PCAP_ERROR_NOT_ACTIVATED if called on a capture handle that has been
       created but not activated.

SEE ALSO
       pcap(3), pcap-linktype(7)

                                 7 April 2014                 PCAP_DATALINK(3)