The members of this structure are

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.

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.

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.

FILES

/etc/networks

DIAGNOSTIC

Null pointer (0) returned on EOF or error.

SEE ALSO

networks(5), RFC 1101

HISTORY

The getnetent(), getnetbyaddr(), getnetbyname(), setnetent(), and endnetent() functions appeared in 4.2BSD.

BUGS

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.

getopt

getopt—Parses command-line options

SYNOPSIS

#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);

DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

longopts is a pointer to the first element of an array of struct option declared in <getopt.h>:

as struct option {

   const char *name;

   int has_arg;

   int *flag;

   int val;

};

The meanings of the different fields are

The last element of the array has to be filled with zeroes.

If longindex is not NULL, it points to a variable that is set to the index of the long option relative to longopts.

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.