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  20 .TH PCAP_DATALINK 3PCAP "7 April 2014"
  21 .SH NAME
  22 pcap_datalink \- get the link-layer header type
  23 .SH SYNOPSIS
  24 .nf
  25 .ft B
  26 #include <pcap/pcap.h>
  27 .ft
  28 .LP
  29 .ft B
  30 int pcap_datalink(pcap_t *p);
  31 .ft
  32 .fi
  33 .SH DESCRIPTION
  34 .BR pcap_datalink ()
  35 returns the link-layer header type for the live capture or ``savefile''
  36 specified by
  37 .IR p .
  38 .PP
  39 It must not be called on a pcap descriptor created by
  40 .BR \%pcap_create (3PCAP)
  41 that has not yet been activated by
  42 .BR \%pcap_activate (3PCAP).
  43 .PP
  44 .I https://www.tcpdump.org/linktypes.html
  45 lists the values
  46 .BR pcap_datalink ()
  47 can return and describes the packet formats that
  48 correspond to those values.
  49 .PP
  50 Do
  51 .B NOT
  52 assume that the packets for a given capture or ``savefile`` will have
  53 any given link-layer header type, such as
  54 .B DLT_EN10MB
  55 for Ethernet.  For example, the "any" device on Linux will have a
  56 link-layer header type of
  57 .B DLT_LINUX_SLL
  58 or
  59 .B DLT_LINUX_SLL2
  60 even if all devices on the system at the time the "any" device is opened
  61 have some other data link type, such as
  62 .B DLT_EN10MB
  63 for Ethernet.
  64 .SH RETURN VALUE
  65 .BR pcap_datalink ()
  66 returns the link-layer header type on success and
  67 .B PCAP_ERROR_NOT_ACTIVATED
  68 if called on a capture handle that has been created but not activated.
  69 .SH SEE ALSO
  70 .BR pcap (3PCAP),
  71 .BR pcap-linktype (@MAN_MISC_INFO@)