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  20 .TH PCAP_OPEN_OFFLINE 3PCAP "12 October 2024"
  21 .SH NAME
  22 pcap_open_offline, pcap_open_offline_with_tstamp_precision,
  23 pcap_fopen_offline, pcap_fopen_offline_with_tstamp_precision \- open a saved capture file for reading
  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 pcap_t *pcap_open_offline(const char *fname, char *errbuf);
  37 pcap_t *pcap_open_offline_with_tstamp_precision(const char *fname,
  38     u_int precision, char *errbuf);
  39 pcap_t *pcap_fopen_offline(FILE *fp, char *errbuf);
  40 pcap_t *pcap_fopen_offline_with_tstamp_precision(FILE *fp,
  41     u_int precision, char *errbuf);
  42 .ft
  43 .fi
  44 .SH DESCRIPTION
  45 .BR pcap_open_offline ()
  46 and
  47 .BR pcap_open_offline_with_tstamp_precision ()
  48 are called to open a ``savefile'' for reading.
  49 .PP
  50 .I fname
  51 specifies the name of the file to open. The file can have the pcap file
  52 format as described in
  53 .BR \%pcap-savefile (@MAN_FILE_FORMATS@),
  54 which is the file format used by, among other programs,
  55 .BR tcpdump (1)
  56 and
  57 .BR tcpslice (1),
  58 or can have the pcapng file format, although not all pcapng files can
  59 be read.
  60 The name "-" is a synonym for
  61 .BR stdin .
  62 .PP
  63 .BR pcap_open_offline_with_tstamp_precision ()
  64 takes an additional
  65 .I precision
  66 argument specifying the time stamp precision desired;
  67 if
  68 .B PCAP_TSTAMP_PRECISION_MICRO
  69 is specified, packet time stamps will be supplied in seconds and
  70 microseconds,
  71 and if
  72 .B PCAP_TSTAMP_PRECISION_NANO
  73 is specified, packet time stamps will be supplied in seconds and
  74 nanoseconds.  If the time stamps in the file do not have the same
  75 precision as the requested precision, they will be scaled up or down as
  76 necessary before being supplied.
  77 .PP
  78 Alternatively, you may call
  79 .BR pcap_fopen_offline ()
  80 or
  81 .BR pcap_fopen_offline_with_tstamp_precision ()
  82 to read dumped data from an existing open stream
  83 .IR fp ;
  84 this stream will be closed by a subsequent call to
  85 .BR pcap_close (3PCAP)
  86 unless it is
  87 .BR stdin .
  88 .BR pcap_fopen_offline_with_tstamp_precision ()
  89 takes an additional
  90 .I precision
  91 argument as described above.
  92 Note that on Windows, that stream should be opened in binary mode.
  93 .PP
  94 .I errbuf
  95 is a buffer large enough to hold at least
  96 .B PCAP_ERRBUF_SIZE
  97 chars.
  98 .SH RETURN VALUE
  99 .BR pcap_open_offline (),
 100 .BR pcap_open_offline_with_tstamp_precision (),
 101 .BR pcap_fopen_offline (),
 102 and
 103 .BR pcap_fopen_offline_with_tstamp_precision ()
 104 return a
 105 .B pcap_t *
 106 on success and
 107 .B NULL
 108 on failure.
 109 If
 110 .B NULL
 111 is returned,
 112 .I errbuf
 113 is filled in with an appropriate error message.
 114 .SH BACKWARD COMPATIBILITY
 115 .BR pcap_open_offline_with_tstamp_precision ()
 116 and
 117 .BR pcap_fopen_offline_with_tstamp_precision ()
 118 became available in libpcap release 1.5.1.  In previous releases, time
 119 stamps from a savefile are always given in seconds and microseconds.
 120 .SH SEE ALSO
 121 .BR pcap (3PCAP),
 122 .BR \%pcap-savefile (@MAN_FILE_FORMATS@)