NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | SEE ALSO | COLOPHON

PCAP_NEXT_EX(3PCAP)                                      PCAP_NEXT_EX(3PCAP)

NAME         top

       pcap_next_ex, pcap_next - read the next packet from a pcap_t

SYNOPSIS         top

       #include <pcap/pcap.h>

       int pcap_next_ex(pcap_t *p, struct pcap_pkthdr **pkt_header,
               const u_char **pkt_data);
       const u_char *pcap_next(pcap_t *p, struct pcap_pkthdr *h);

DESCRIPTION         top

       pcap_next_ex() reads the next packet and returns a success/failure
       indication.  If the packet was read without problems, the pointer
       pointed to by the pkt_header argument is set to point to the
       pcap_pkthdr struct for the packet, and the pointer pointed to by the
       pkt_data argument is set to point to the data in the packet.  The
       struct pcap_pkthdr and the packet data are not to be freed by the
       caller, and are not guaranteed to be valid after the next call to
       pcap_next_ex(), pcap_next(), pcap_loop(), or pcap_dispatch(); if the
       code needs them to remain valid, it must make a copy of them.

       pcap_next() reads the next packet (by calling pcap_dispatch() with a
       cnt of 1) and returns a u_char pointer to the data in that packet.
       The packet data is not to be freed by the caller, and is not
       guaranteed to be valid after the next call to pcap_next_ex(),
       pcap_next(), pcap_loop(), or pcap_dispatch(); if the code needs it to
       remain valid, it must make a copy of it.  The pcap_pkthdr structure
       pointed to by h is filled in with the appropriate values for the
       packet.

       The bytes of data from the packet begin with a link-layer header.
       The format of the link-layer header is indicated by the return value
       of the pcap_datalink() routine when handed the pcap_t value also
       passed to pcap_loop() or pcap_dispatch().
       http://www.tcpdump.org/linktypes.html  lists the values
       pcap_datalink() can return and describes the packet formats that
       correspond to those values.  The value it returns will be valid for
       all packets received unless and until pcap_set_datalink() is called;
       after a successful call to pcap_set_datalink(), all subsequent
       packets will have a link-layer header of the type specified by the
       link-layer header type value passed to pcap_set_datalink().

       Do NOT assume that the packets for a given capture or ``savefile``
       will have any given link-layer header type, such as DLT_EN10MB for
       Ethernet.  For example, the "any" device on Linux will have a link-
       layer header type of DLT_LINUX_SLL even if all devices on the system
       at the time the "any" device is opened have some other data link
       type, such as DLT_EN10MB for Ethernet.

RETURN VALUE         top

       pcap_next_ex() returns 1 if the packet was read without problems, 0
       if packets are being read from a live capture and the packet buffer
       timeout expired, -1 if an error occurred while reading the packet,
       and -2 if packets are being read from a ``savefile'' and there are no
       more packets to read from the savefile.  If -1 is returned,
       pcap_geterr() or pcap_perror() may be called with p as an argument to
       fetch or display the error text.

       pcap_next() returns a pointer to the packet data on success, and
       returns NULL if an error occurred, or if no packets were read from a
       live capture (if, for example, they were discarded because they
       didn't pass the packet filter, or if, on platforms that support a
       packet buffer timeout that starts before any packets arrive, the
       timeout expires before any packets arrive, or if the file descriptor
       for the capture device is in non-blocking mode and no packets were
       available to be read), or if no more packets are available in a
       ``savefile.'' Unfortunately, there is no way to determine whether an
       error occurred or not.

SEE ALSO         top

       pcap(3PCAP), pcap_geterr(3PCAP), pcap_dispatch(3PCAP),
       pcap_datalink(3PCAP)

COLOPHON         top

       This page is part of the libpcap (packet capture library) project.
       Information about the project can be found at 
       ⟨http://www.tcpdump.org/⟩.  If you have a bug report for this manual
       page, see ⟨http://www.tcpdump.org/#patches⟩.  This page was obtained
       from the project's upstream Git repository 
       ⟨https://github.com/the-tcpdump-group/libpcap.git⟩ on 2017-09-15.  If
       you discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for the
       page, or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page), send a
       mail to man-pages@man7.org

                               20 January 2017           PCAP_NEXT_EX(3PCAP)