Index for Section 3

Alphabetical listing for G

Bottom of page

getopt(3)
NAME
  getopt - Gets flag letters from the argument vector

LIBRARY
  Standard C Library (libc)

SYNOPSIS
  #include <unistd.h>

  int getopt(
	  int argc,
	  char * const argv[],
	  const char *optstring);

  extern char *optarg;

  extern int optind;

  extern int opterr;

  extern int optopt;

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  getopt(): XSH5.0

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  argc	    Specifies the number of parameters passed to the routine.

  argv	    Points to an array of argc pointers to argument strings.

  optstring Specifies a string of recognized flag characters.  If a character
	    is followed by a : (colon), the flag is expected to take a
	    parameter that may or may not be separated from it by white
	    space.

DESCRIPTION
  The getopt() function parses argument lists. It returns the next flag
  character in the argv parameter list that matches a character in the
  optstring parameter. If that flag takes an argument, the getopt() function
  has the optarg variable point to the flag argument according to the
  following rules:

    ·  If the flag is the last character pointed to by an argv element,
       optarg will contain argv's next element, and optind is incremented by
       2. The getopt() function returns an error if the resulting optind is
       greater than or equal to argc.

    ·  If the flag is not the last character, then the optarg variable points
       to the string after the flag character in the associated element of
       argv. The optind variable is incremented by 1.

  The optarg external variable is set to point to the start of the flag's
  parameter on return from the getopt() function.

  The getopt() function places the argv index of the next argument to be
  processed in optind. The optind variable is externally initialized to 1
  before the first call to getopt() so that argv[0] is not processed. Error
  messages can be suppressed by providing a value of 0 (zero) as the opterr
  parameter.

NOTES
  [Tru64 UNIX]	The external int optopt variable is set to the real flag
  found in the argv parameter. This is true whether the flag is in the
  optstring parameter or not.

EXAMPLES
  The following example shows a suggested way to use the getopt() function.

       #include <unistd.h>
       main(argc, argv)
       int     argc;
       char    *argv[];

       #define ARGS    "r:w:f:s"

       {
	       int     c, errflg = 0;
	       int     readers = 1, writers = 1;
	       int     freeBufs = 1;
	       int     doStats = FALSE;

	       optarg = NULL;
	       while (!errflg && ((c = getopt(argc, argv, ARGS)) != -1))
		       switch (c) {
		       case 'r'	       :
			       readers = atoi(optarg);
			       break;
		       case 'w'	       :
			       writers = atoi(optarg);
			       break;
		       case 'f'	       :
			       freeBufs = atoi(optarg);
			       break;
		       case 's'	       :
			       doStats = TRUE;
			       break;
		       default :
			       errflg++;
		       }

RETURN VALUES
  Upon successful completion, the getopt() function returns the flag
  character that was detected.	If the function encounters a flag that is not
  included in the optstring parameter, or if the : (colon) character is used
  incorrectly, the getopt() function prints an error message on stderr and
  returns a ? (question mark).	If there is a missing flag, the getopt()
  function returns a : (colon) if optstring's first character is a : (colon),
  and a ? (question mark) otherwise.  In addition, the getopt() function sets
  the optopt variable to the flag character that caused one of these errors.

  The getopt() function also displays a diagnostic message if the application
  did not set the opterr variable to 0 (zero), and optstring's first
  character is not a : (colon).

  When all flags have been processed (that is, up to the first nonflag
  argument), the getopt() function returns a value of -1.  The special flag
  -- (dash dash) can be used to delimit the end of the flags; -1 is returned,
  and the -- (dash dash) string is skipped.

  The getopt() function does not change optind, and also returns a value of
  -1, if one of the following occurs:

    ·  The argv[optind] result is NULL.

    ·  The *argv[optind] result is not the special - (dash) flag.

    ·  The argv[optind] result points to the - (dash) string.

  The getopt() function does increment optind if the result of argv[optind]
  points to the -- (dash dash) string.

RELATED INFORMATION
  Commands: getopt(1)

  Standards: standards(5)

Index for Section 3

Alphabetical listing for G

Top of page