pcap_open_offline(3PCAP) man page

Updated: 23 August 2018 • View in plain textReturn to Main Contents

This man page documents libpcap version 1.10.0 (see also: git master branch, 1.10.4, 1.10.2, 1.10.1, 1.9.1, 1.8.1, 1.7.4, 1.6.2, 1.5.3).

Your system may have a different version installed, possibly with some local modifications. To achieve the best results, please make sure this version of this man page suits your needs. If necessary, try to look for a different version on this web site or in the man pages available in your installation.


pcap_open_offline, pcap_open_offline_with_tstamp_precision, pcap_fopen_offline, pcap_fopen_offline_with_tstamp_precision - open a saved capture file for reading


#include <pcap/pcap.h>

char errbuf[PCAP_ERRBUF_SIZE];

pcap_t *pcap_open_offline(const char *fname, char *errbuf);
pcap_t *pcap_open_offline_with_tstamp_precision(const char *fname,
    u_int precision, char *errbuf);
pcap_t *pcap_fopen_offline(FILE *fp, char *errbuf);
pcap_t *pcap_fopen_offline_with_tstamp_precision(FILE *fp,
    u_int precision, char *errbuf);


pcap_open_offline() and pcap_open_offline_with_tstamp_precision() are called to open a ``savefile'' for reading.

fname specifies the name of the file to open. The file can have the pcap file format as described in pcap-savefile(5), which is the file format used by, among other programs, tcpdump(1) and tcpslice(1), or can have the pcapng file format, although not all pcapng files can be read. The name "-" is a synonym for stdin.

pcap_open_offline_with_tstamp_precision() takes an additional precision argument specifying the time stamp precision desired; if PCAP_TSTAMP_PRECISION_MICRO is specified, packet time stamps will be supplied in seconds and microseconds, and if PCAP_TSTAMP_PRECISION_NANO is specified, packet time stamps will be supplied in seconds and nanoseconds. If the time stamps in the file do not have the same precision as the requested precision, they will be scaled up or down as necessary before being supplied.

Alternatively, you may call pcap_fopen_offline() or pcap_fopen_offline_with_tstamp_precision() to read dumped data from an existing open stream fp. pcap_fopen_offline_with_tstamp_precision() takes an additional precision argument as described above. Note that on Windows, that stream should be opened in binary mode.


pcap_open_offline(), pcap_open_offline_with_tstamp_precision(), pcap_fopen_offline(), and pcap_fopen_offline_with_tstamp_precision() return a pcap_t * on success and NULL on failure. If NULL is returned, errbuf is filled in with an appropriate error message. errbuf is assumed to be able to hold at least PCAP_ERRBUF_SIZE chars.


pcap_open_offline_with_tstamp_precision() and pcap_fopen_offline_with_tstamp_precision() became available in libpcap release 1.5.1. In previous releases, time stamps from a savefile are always given in seconds and microseconds.


pcap(3PCAP), pcap-savefile(5)


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