Parses command line arguments and parameter lists.
#include <getopt.h>
int getopt (
int argc,
char * const argv[],
const char *optstr);
(IN) Specifies the number of arguments in the array.
(IN) Specifies the argument array.
(IN) Points to option characters. If a character is followed by a colon, the option takes an argument.
If successful, returns the next option character specified on the command line. Returns -1 when all options are parsed.
If an error occurs, returns
A colon if the function detects a missing argument and the first character of optstr was a colon.
A question mark if the function encounters an option character not in optstr or detects a missing argument and the first character of optstr was not a colon.
On return from the getopt function, the following variables are set:
optarg—points to an option argument, if one exists.
optind—contains the index to the next argv argument for a subsequent call to getopt.
opterr—before the first call, initialized to 1.
optopt—saves the last known option character returned by getopt.
optreset—before the first call, initialized to 1.
You can set the optind to another value before a set of calls to getopt in order to skip over more or less argv entries.
To use getopt to evaluate multiple sets of arguments, or to evaluate a single set of arguments multiple times, you must set the variable optreset to 1 before the second and each additional set of calls to getopt, and the variable optind must be reinitialized.