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.TH PCAP_COMPILE 3PCAP "22 August 2018"

.SH NAME

pcap_compile \- compile a filter expression

.SH SYNOPSIS

.nf

.ft B

#include <pcap/pcap.h>

.ft

.LP

.ft B

int pcap_compile(pcap_t *p, struct bpf_program *fp,

.ti +8

const char *str, int optimize, bpf_u_int32 netmask);

.ft

.fi

.SH DESCRIPTION

.B pcap_compile()

is used to compile the string

.I str

into a filter program.  See

.BR pcap-filter (@MAN_MISC_INFO@)

for the syntax of that string.

.I program

is a pointer to a

.I bpf_program

struct and is filled in by

.BR pcap_compile() .

.I optimize

controls whether optimization on the resulting code is performed.

.I netmask

specifies the IPv4 netmask of the network on which packets are being

captured; it is used only when checking for IPv4 broadcast addresses in

the filter program.  If the netmask of the network on which packets are

being captured isn't known to the program, or if packets are being

captured on the Linux "any" pseudo-interface that can capture on more

than one network, a value of

.B PCAP_NETMASK_UNKNOWN

can be supplied; tests

for IPv4 broadcast addresses will fail to compile, but all other tests in

the filter program will be OK.

.LP

NOTE: in libpcap 1.8.0 and later,

.B pcap_compile()

can be used in multiple threads within a single process.  However, in

earlier versions of libpcap, it is

.I not

safe to use

.B pcap_compile()

in multiple threads in a single process without some form of mutual

exclusion allowing only one thread to call it at any given time.

.SH RETURN VALUE

.B pcap_compile()

returns 0 on success and

.B PCAP_ERROR

on failure. If

.B PCAP_ERROR

is returned,

.B pcap_geterr(3PCAP)

or

.B pcap_perror(3PCAP)

may be called with

.I p

as an argument to fetch or display the error text.

.SH BACKWARD COMPATIBILITY

.PP

The

.B PCAP_NETMASK_UNKNOWN

constant became available in libpcap release 1.1.0.

.SH SEE ALSO

pcap(3PCAP), pcap_setfilter(3PCAP), pcap_freecode(3PCAP),