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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

.B 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

.B \%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

.B 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

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

.B 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

pcap(3PCAP), pcap-linktype(@MAN_MISC_INFO@)