Content-type: text/html Man page of getopt

getopt

Section: C Library Functions (3)
Index Return to Main Contents
 

NAME

getopt - Gets flag letters from the argument vector  

LIBRARY

Standard C Library (libc.so, libc.a)  

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():  XPG4, XPG4-UNIX

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

PARAMETERS

Specifies the number of parameters passed to the routine. Points to an array of argc pointers to argument strings. 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

[Digital]  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) delim off


 

Index

NAME
LIBRARY
SYNOPSIS
STANDARDS
PARAMETERS
DESCRIPTION
NOTES
EXAMPLES
RETURN VALUES
RELATED INFORMATION

This document was created by man2html, using the manual pages.
Time: 02:41:15 GMT, October 02, 2010