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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
.BR 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,
.BR 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
.BR 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
.BR pcap_compile ()
returns
.B 0
on success and
.B PCAP_ERROR
on failure. If
.B PCAP_ERROR
is returned,
.BR pcap_geterr (3PCAP)
or
.BR 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
.BR pcap (3PCAP),
.BR pcap_setfilter (3PCAP),
.BR pcap_freecode (3PCAP)