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<A NAME="PAGENUM-937"><P>Page 937</P></A>
<P>The members of this structure are</P>
<TABLE>
<TR><TD>
n_name
</TD><TD>
The official name of the network.
</TD></TR><TR><TD>
n_aliases
</TD><TD>
A zero-terminated list of alternate names for the network.
</TD></TR><TR><TD>
n_addrtype
</TD><TD>
The type of the network number returned:
AF_INET.
</TD></TR><TR><TD>
n_net
</TD><TD>
The network number. Network numbers are returned in machine byte order.
</TD></TR></TABLE>
<P>If the stayopen flag on a setnetent subroutine is
NULL, the network database is opened. Otherwise the
setnetent has the effect of rewinding the network database. The
endnetent may be called to close the network database when processing is complete.</P>
<P>The getnetent subroutine simply reads the next line whereas
getnetbyname and getnetbyaddr search until a matching
name or net number is found (or until EOF is encountered). The
type must be AF_INET. The getnetent subroutine keeps a pointer
in the database, allowing successive calls to be used to search the entire file.</P>
<P>A call to setnetent must be made before a while loop using
getnetent to perform initialization, and an
endnetent must be used after the loop. Both
getnetbyname and getnetbyaddr make calls to
setnetent and endnetent.</P>
<P><B>
FILES
</P></B>
<!-- CODE SNIP //-->
<PRE>
/etc/networks
</PRE>
<!-- END CODE SNIP //-->
<P><B>
DIAGNOSTIC
</P></B>
<P>Null pointer (0) returned on EOF or error.</P>
<P></B>SEE ALSO
</P></B>
<P>networks(5), RFC 1101
<P><B>
HISTORY
</P></B>
<P>The getnetent(), getnetbyaddr(), getnetbyname(),
setnetent(), and endnetent() functions appeared in 4.2BSD.</P>
<P><B>BUGS
</P></B>
<P>The data space used by these functions is static; if future use requires the data, it should be copied before any subsequent
calls to these functions overwrite it. Only Internet network numbers are currently understood. Expecting network numbers to
fit in no more than 32 bits is probably naive.</P>
<H3><A NAME="ch03_ 84">
getopt
</A></H3>
<P>getopt—Parses command-line options</P>
<P><B>SYNOPSIS
</P></B>
<!-- CODE //-->
<PRE>
#include <unistd.h>
int getopt(int argc, char * const argv[],
const char *optstring);
extern char *optarg;
extern int optind, opterr, optopt;
#include <getopt.h>
int getopt_long(int argc, char * const argv[],
const char *optstring,
const struct option *longopts, int *longindex);
int getopt_long_only(int argc, char * const argv[],
const char *optstring,
const struct option *longopts, int *longindex);
</PRE>
<!-- END CODE //-->
<A NAME="PAGENUM-938"><P>Page 938</P></A>
<P><B>DESCRIPTION
</P></B>
<P>The getopt() function parses the command-line arguments. Its arguments
argc and argv are the argument count and array as passed to the
main() function on program invocation. An element of
argv that starts with - (and is not exactly - or
_-) is an option element. The characters of this element (aside from the initial
-) are option characters. If getopt() is called
repeatedly, it returns successively each of the option characters from each of the option elements.</P>
<P>If getopt() finds another option character, it returns that character, updating the external variable
optind and a static variable nextchar so that the next call to
getopt() can resume the scan with the following option character or
argv element.</P>
<P>If there are no more option characters,
getopt() returns EOF. Then optind is the index in
argv of the first argv element that is not an option.</P>
<P>optstring is a string containing the legitimate option characters. If such a character is followed by a colon, the
option requires an argument, so getopt places a pointer to the following text in the same
argv element, or the text of the following argv element, in
optarg. Two colons mean an option takes an optional
arg; if there is text in the current argv element, it
is returned in optarg; otherwise, optarg is set to
0.</P>
<P>By default, getargs() permutes the contents of
argv as it scans, so that eventually all the non-options are at the end.
Two other modes are also implemented. If the first character of
optstring is + or the environment variable
POSIXLY_CORRECT is set, option processing stops as soon as a non-option argument is encountered. If the first character of optstring is
-, each non-option argv element is handled as if it were the argument of an option with character code 1. (This is used by programs
that were written to expect options and other argv elements in any order and that care about the ordering of the two.) The
special argument _ forces an end of option-scanning regardless of the scanning mode.</P>
<P>If getopt() does not recognize an option character, it prints an error message to
stderr, stores the character in optopt, and
returns?. The calling program may prevent the error message by setting
opterr to 0.</P>
<P>The getopt_long()function works like getopt(), except that it also accepts long options, started out by two dashes.
Long option names may be abbreviated if the abbreviation is unique or is an exact match for some defined option. A long
option may take a parameter, of the form
-_arg=param or _-arg param.</P>
<P>longopts is a pointer to the first element of an array of
struct option declared in <getopt.h>:</P>
<!-- CODE SNIP //-->
<PRE>
as struct option {
const char *name;
int has_arg;
int *flag;
int val;
};
</PRE>
<!-- END CODE SNIP //-->
<P>The meanings of the different fields are</P>
<TABLE>
<TR><TD>
name
</TD><TD>
The name of the long option.
</TD></TR><TR><TD>
has_arg
</TD><TD>
no_argument (or 0) if the option does not take an argument,
required_argument (or 1) if the option requires an argument, or
optional_argument (or 2) if the option takes an
optional argument.
</TD></TR><TR><TD>
flag
</TD><TD>
Specifies how results are returned for a long option. If
flag is NULL, getopt_long() returns val. (For example, the calling program might set
val to the equivalent short option character.) Otherwise,
getopt_long() returns 0, and flag points to a variable that is set to
val if the option is found, but left unchanged if the option is not found.
</TD></TR><TR><TD>
val
</TD><TD>
The value to return or to load into the variable pointed to by
flag.
</TD></TR></TABLE>
<P>The last element of the array has to be filled with zeroes.</P>
<P>If longindex is not NULL, it points to a variable that is set to the index of the long option relative to
longopts.</P>
<P>getopt_long_only() is like getopt_long(), but - as well as
-_ can indicate a long option. If an option that starts with
- (not _-) doesn't match a long option but does match a short option, it is parsed as a short option instead.</P>
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