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  20 .TH PCAP_SETNONBLOCK 3PCAP "25 July 2018"
  21 .SH NAME
  22 pcap_setnonblock, pcap_getnonblock \- set or get the state of
  23 non-blocking mode on a capture device
  24 .SH SYNOPSIS
  25 .nf
  26 .ft B
  27 #include <pcap/pcap.h>
  28 .ft
  29 .LP
  30 .nf
  31 .ft B
  32 char errbuf[PCAP_ERRBUF_SIZE];
  33 .ft
  34 .LP
  35 .ft B
  36 int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
  37 int pcap_getnonblock(pcap_t *p, char *errbuf);
  38 .ft
  39 .fi
  40 .SH DESCRIPTION
  41 .B pcap_setnonblock()
  42 puts a capture handle into ``non-blocking'' mode, or takes it out
  43 of ``non-blocking'' mode, depending on whether the
  44 .I nonblock
  45 argument is non-zero or zero.  It has no effect on ``savefiles''.
  46 If there is an error,
  47 .B PCAP_ERROR
  48 is returned and
  49 .I errbuf
  50 is filled in with an appropriate error message; otherwise, 0 is
  51 returned.
  52 In
  53 ``non-blocking'' mode, an attempt to read from the capture descriptor
  54 with
  55 .BR pcap_dispatch (3PCAP)
  56 will, if no packets are currently available to be read, return 0
  57 immediately rather than blocking waiting for packets to arrive.
  58 .BR pcap_loop (3PCAP)
  59 and
  60 .BR pcap_next (3PCAP)
  61 will not work in ``non-blocking'' mode.
  62 .PP
  63 When first activated with
  64 .BR pcap_activate (3PCAP)
  65 or opened with
  66 .BR pcap_open_live (3PCAP) ,
  67 a capture handle is not in ``non-blocking mode''; a call to
  68 .B pcap_setnonblock()
  69 is required in order to put it into ``non-blocking'' mode.
  70 .SH RETURN VALUE
  71 .B pcap_getnonblock()
  72 returns the current ``non-blocking'' state of the capture descriptor; it
  73 always returns 0 on ``savefiles''.
  74 If there is an error,
  75 .B PCAP_ERROR
  76 is returned and
  77 .I errbuf
  78 is filled in with an appropriate error message.
  79 .PP
  80 .I errbuf
  81 is assumed to be able to hold at least
  82 .B PCAP_ERRBUF_SIZE
  83 chars.
  84 .SH SEE ALSO
  85 .BR pcap (3PCAP),
  86 .BR pcap_next_ex (3PCAP),
  87 .BR pcap_geterr (3PCAP)