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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |SEE ALSO |COLOPHON | |
PCAP_NEXT_EX(3PCAP)PCAP_NEXT_EX(3PCAP)pcap_next_ex, pcap_next - read the next packet from a pcap_t
#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);
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 thepkt_header argument is set to point to thepcap_pkthdrstruct for the packet, and the pointer pointed to by thepkt_data argument is set to point to the data in the packet. Thestruct pcap_pkthdrand the packet data are not to be freed by the caller, and are not guaranteed to be valid after the next call topcap_next_ex(),pcap_next(),pcap_loop(3PCAP), orpcap_dispatch(3PCAP); if the code needs them to remain valid, it must make a copy of them.pcap_next() reads the next packet (by callingpcap_dispatch() with acnt of 1) and returns au_charpointer 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 topcap_next_ex(),pcap_next(),pcap_loop(), orpcap_dispatch(); if the code needs it to remain valid, it must make a copy of it. Thepcap_pkthdr structure pointed to byh 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 thepcap_datalink(3PCAP) routine when handed thepcap_t value also passed topcap_loop() orpcap_dispatch().https://www.tcpdump.org/linktypes.html lists the valuespcap_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 untilpcap_set_datalink(3PCAP) is called; after a successful call topcap_set_datalink(), all subsequent packets will have a link-layer header of the type specified by the link-layer header type value passed topcap_set_datalink(). DoNOTassume that the packets for a given capture or ``savefile`` will have any given link-layer header type, such asDLT_EN10MBfor Ethernet. For example, the "any" device on Linux will have a link-layer header type ofDLT_LINUX_SLLorDLT_LINUX_SLL2even if all devices on the system at the time the "any" device is opened have some other data link type, such asDLT_EN10MBfor Ethernet.
pcap_next_ex() returns1if the packet was read without problems,0if packets are being read from a live capture and the packet buffer timeout expired,PCAP_ERROR_BREAKif packets are being read from a ``savefile'' and there are no more packets to read from the savefile,PCAP_ERROR_NOT_ACTIVATEDif called on a capture handle that has been created but not activated, orPCAP_ERRORif an error occurred while reading the packet. IfPCAP_ERRORis returned,pcap_geterr(3PCAP) orpcap_perror(3PCAP) may be called withp as an argument to fetch or display the error text.pcap_next() returns a pointer to the packet data on success, and returnsNULLif 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.
pcap(3PCAP)
This page is part of thelibpcap (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 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-08-10.) 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 isnot part of the original manual page), send a mail to man-pages@man7.org 5 March 2022PCAP_NEXT_EX(3PCAP)HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |