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.TH PCAP_DATALINK 3PCAP "7 April 2014"
.SH NAME
pcap_datalink \- get the link-layer header type
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.ft
.LP
.ft B
int pcap_datalink(pcap_t *p);
.ft
.fi
.SH DESCRIPTION
.BR pcap_datalink ()
returns the link-layer header type for the live capture or ``savefile''
specified by
.IR p .
.PP
It must not be called on a pcap descriptor created by
.BR \%pcap_create (3PCAP)
that has not yet been activated by
.BR \%pcap_activate (3PCAP).
.PP
.I https://www.tcpdump.org/linktypes.html
lists the values
.BR pcap_datalink ()
can return and describes the packet formats that
correspond to those values.
.PP
Do
.B NOT
assume that the packets for a given capture or ``savefile`` will have
any given link-layer header type, such as
.B DLT_EN10MB
for Ethernet.  For example, the "any" device on Linux will have a
link-layer header type of
.B DLT_LINUX_SLL
or
.B DLT_LINUX_SLL2
even if all devices on the system at the time the "any" device is opened
have some other data link type, such as
.B DLT_EN10MB
for Ethernet.
.SH RETURN VALUE
.BR pcap_datalink ()
returns the link-layer header type on success and
.B PCAP_ERROR_NOT_ACTIVATED
if called on a capture handle that has been created but not activated.
.SH SEE ALSO
.BR pcap (3PCAP),
.BR pcap-linktype (@MAN_MISC_INFO@)