pcap_compile - compile a filter expression
int pcap_compile(pcap_t *p, struct bpf_program *fp,
const char *str, int optimize, bpf_u_int32 netmask);
pcap_compile() is used to compile the string str into a filter
program. See pcap-filter(7) for the syntax of that string.
program is a pointer to a bpf_program struct and is filled in by
pcap_compile(). optimize controls whether optimization on the
resulting code is performed. 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 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.
pcap_compile() returns 0 on success and -1 on failure. 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(3PCAP), pcap_setfilter(3PCAP), pcap_freecode(3PCAP), pcap_geterr(3PCAP),