CGETOPT_LONG

Section: Common Library (3)
Updated: $Date: 2010-04-05 09:51:26 +0200 (Mon, 05 Apr 2010) $
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NAME

Cgetopt_long - get long options from command line argument list

SYNOPSIS

#include <Cgetopt.h>

int Cgetopt (int argc, char **argv, char *optstring)
int Cgetopt_long (int argc, char **argv, char *optstring, Coptions_t *long_options, int *index)

DESCRIPTION

The Cgetopt function incrementally parses a command line argument list argv and returns the next known option character. An option character is known if it has been specified in the string of accepted option characters optstring. The Cgetopt_long function is similar to Cgetopt but it accepts options in two forms: words and characters. The Cgetopt_long function provides a superset of the functionality of Cgetopt. The additional functionality is described in the section CGETOPT_LONG. The option string optstring may contain the following elements: individual characters, and characters followed by a colon to indicate an option argument is to follow. For example, an option string x recognizes an option x , and an option string x: recognizes an option x taking an argument. It does not matter to Cgetopt if a following argument has leading white space. On return from Cgetopt, Coptarg points to an option argument, if it is anticipated, and the variable Coptind contains the index to the next argv argument for a subsequent call to Cgetopt. The variable Coptopt saves the last known option character returned by Cgetopt. The variables Copterr and Coptind are both initialized to 1. The Coptind variable may be set to another value before a set of calls to Cgetopt in order to skip over more or less argv entries. In order to use Cgetopt to evaluate multiple sets of arguments, or to evaluate a single set of arguments multiple times, the variable Coptreset must be set to 1 before the second and each additional set of calls to Cgetopt and the variable Coptind must be reinitialized. The Cgetopt function returns -1 when the argument list is exhausted, or a non-recognized option is encountered. The interpretation of options in the argument list may be cancelled by the option -- (double dash) which causes Cgetopt to signal the end of argument processing and returns -1. When all options have been processed (i.e., up to the first non-option argument), Cgetopt returns -1. Cgetopt_long can be used in two ways. In the first way, every long option understood by the program has a coresponding short option, and the option structure is only used to translate from long option to short options. When used in this fashion, Cgetopt_long behaves identically to Cgetopt. This is good way to add long option processing to an existing program with the minimum of rewriting. In the second mechanism, a long option set a flag in the Coptions_t structure passed, or will store a pointer to the command line argument in the Coptions_t structure passed to it for options that take arguments. Additionally, the long option's argument may be specified as a single argument with an equal sign, e.g myprogram --myoption=somevalue When a long option is processed the call to Cgetopt_long will return 0. For this reason, long option processing without shortcuts are not backwards compatible with Cgetopt. It is possible to combine these methods, providing for long options processing with short option equivalents for some options. Less frequently used options would be processed as long options only.

USAGE OF CGETOPT_LONG

The Cgetopt_long call requires a structure to be initialized describing the long options. The structure is:


Coptions_t {
    char *name;
    int has_arg;
    int *flag;
    int val;
};

The name field should contain the option name without the leading double dash. The has_arg field should be one of: NO_ARGUMENT if no argument to the option is expected, REQUIRED_ARGUMENT if an argument to the option is required or OPTIONAL_ARGUMENT if an argument to the option may be presented. If flag is non-NULL, then the integer pointed to by it will set to the value in the val field. If the flag field is NULL, then the val field will be returned. Setting flag to NULL and setting val to the corresponding short option will make this function act just like Cgetopt.

DIAGNOSTICS

If the Cgetopt function encounters a character not found in the string optstring or detects a missing option argument it writes an error message to stderr and returns ?. Setting Copterr to a zero will disable these error messages. If optstring has a leading : then a missing option argument causes a : to be returned in addition to suppressing any error messages. Option arguments are allowed to begin with - ; this is reasonable but reduces the amount of error checking possible.

CGETOPT_LONG EXTENSIONS

The Coptreset variable was added to make it possible to call the Cgetopt function multiple times. This is an extension to the -p1003.2 specification.

EXAMPLE


#include <Cgetopt.h>
int bflag, ch, fd;

Coptind = 1;            /* Required */
Copterr = 1;            /* Some stderr output if you want */

bflag = 0;
while ((ch = Cgetopt(argc, argv, "bf:")) != -1)
        switch(ch) {
        case 'b':
                bflag = 1;
                break;
        case 'f':
                if ((fd = open(Coptarg, O_RDONLY, 0)) < 0) {
                        (void)fprintf(stderr,
                            "myname: %s: %s\n", Coptarg, strerror(errno));
                        exit(1);
                }
                break;
        case '?':
        default:
                usage();
}
argc -= Coptind;
argv += Coptind;

LONG EXAMPLE


#include <Cgetopt.h>
int bflag, ch, fd;
int daggerset;

/* options descriptor */
Coptions_t longopts[] =
{
  {"buffy",       NO_ARGUMENT,        NULL,      'b'},
  {"floride",     REQUIRED_ARGUMENT,  NULL,      'f'},
  {"daggerset",   NO_ARGUMENT,        &daggerset,  1},
  {NULL,          0,                  NULL,        0}
};

Coptind = 1;            /* Required */
Copterr = 1;            /* Some stderr output if you want */

bflag = 0;
while ((ch = Cgetopt_long(argc, argv, "bf:", longopts, NULL)) != -1)
        switch(ch) {
        case 'b':
                bflag = 1;
                break;
        case 'f':
                if ((fd = open(Coptarg, O_RDONLY, 0)) < 0) {
                        (void)fprintf(stderr,
                            "myname: %s: %s\n", Coptarg, strerror(errno));
                        exit(1);
                }
                break;
        case 0:
                if(daggerset) {
                        fprintf(stderr,"Buffy will put use her dagger"
                                       "to apply floride to dracula's teeth");
                }
                break;
        case '?':
        default:
                usage();
}
argc -= Coptind;
argv += Coptind;

HISTORY

The Cgetopt function appeared in BSD 4.3. The Cgetopt_long function first appeared in GNU library. This implementation was imported to NetBSD from a Kerberos distribution.

BUGS

The Cgetopt function was once specified to return EOF instead of -1. This was changed by -p1003.2-92 to decouple Cgetopt from <stdio.h>. A single dash - may be specified as an character in optstring, however it should never have an argument associated with it. This allows Cgetopt to be used with programs that expect - as an option flag. This practice is wrong, and should not be used in any current development. It is provided for backward compatibility only. By default, a single dash causes Cgetopt to return -1. This is, we believe, compatible with System V. It is also possible to handle digits as option letters. This allows Cgetopt to be used with programs that expect a number -3 as an option. This practice is wrong, and should not be used in any current development. It is provided for backward compatibility only. The following code fragment works in most cases.


int length;
char *p;

Coptind = 1;            /* Required */
Copterr = 1;            /* Some stderr output if you want */

while ((c = Cgetopt(argc, argv, "0123456789")) != -1)
        switch (c) {
        case '0': case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9':
                p = argv[Coptind - 1];
                if (p[0] == '-' && p[1] == ch && !p[2])
                        length = atoi(++p);
                else
                        length = atoi(argv[Coptind] + 1);
                break;
        }
}

The OPTIONAL_ARGUMENT always eats the following argument unless the argument is included via the --option=argument notation.

AUTHOR

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