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pcap_dump_open, pcap_dump_open_append, pcap_dump_fopen - open a file to which to write packets


#include <pcap/pcap.h>

pcap_dumper_t *pcap_dump_open(pcap_t *p, const char *fname);
pcap_dumper_t *pcap_dump_open_append(pcap_t *p, const char *fname);
pcap_dumper_t *pcap_dump_fopen(pcap_t *p, FILE *fp);


pcap_dump_open() is called to open a ``savefile'' for writing. fname specifies the name of the file to open. The file will have the same format as those used by tcpdump(1) and tcpslice(1). If the file does not exist, it will be created; if the file exists, it will be truncated and overwritten. The name "-" is a synonym for stdout.

pcap_dump_fopen() is called to write data to an existing open stream fp; this stream will be closed by a subsequent call to pcap_dump_close(3PCAP). The stream is assumed to be at the beginning of a file that has been newly created or truncated, so that writes will start at the beginning of the file. Note that on Windows, that stream should be opened in binary mode.

p is a capture or ``savefile'' handle returned by an earlier call to pcap_create(3PCAP) and activated by an earlier call to pcap_activate(3PCAP), or returned by an earlier call to pcap_open_offline(3PCAP), pcap_open_live(3PCAP), or pcap_open_dead(3PCAP). The time stamp precision, link-layer type, and snapshot length from p are used as the link-layer type and snapshot length of the output file.

pcap_dump_open_append() is like pcap_dump_open() but, if the file already exists, and is a pcap file with the same byte order as the host opening the file, and has the same time stamp precision, link-layer header type, and snapshot length as p, it will write new packets at the end of the file.


A pointer to a pcap_dumper_t structure to use in subsequent pcap_dump(3PCAP) and pcap_dump_close(3PCAP) calls is returned on success. NULL is returned on failure. If NULL is returned, pcap_geterr(3PCAP) can be used to get the error text.


The pcap_dump_open_append() function became available in libpcap release 1.7.2. In previous releases, there is no support for appending packets to an existing savefile.


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

3 July 2020