Manpage of GETSUBOPT

GETSUBOPT

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

getsubopt - parse suboption arguments from a string  

SYNOPSIS

#include <stdlib.h>

int getsubopt(char **optionp, char * const *tokens, char **valuep);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

getsubopt():

_XOPEN_SOURCE >= 500

    || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
 

DESCRIPTION

getsubopt() parses the list of comma-separated suboptions provided in optionp. (Such a suboption list is typically produced when getopt(3) is used to parse a command line; see for example the -o option of mount(8).) Each suboption may include an associated value, which is separated from the suboption name by an equal sign. The following is an example of the kind of string that might be passed in optionp:

ro,name=xyz

The tokensargument is a pointer to a NULL-terminated array of pointers to the tokens that getsubopt() will look for in optionp. The tokens should be distinct, null-terminated strings containing at least one character, with no embedded equal signs or commas.

Each call to getsubopt() returns information about the next unprocessed suboption in optionp. The first equal sign in a suboption (if any) is interpreted as a separator between the name and the value of that suboption. The value extends to the next comma, or (for the last suboption) to the end of the string. If the name of the suboption matches a known name from tokens, and a value string was found, getsubopt() sets *valuepto the address of that string. The first comma in optionpis overwritten with a null byte, so *valuepis precisely the "value string" for that suboption.

If the suboption is recognized, but no value string was found, *valuepis set to NULL.

When getsubopt() returns, optionppoints to the next suboption, or to the null byte (aq\0aq) at the end of the string if the last suboption was just processed.  

RETURN VALUE

If the first suboption in optionpis recognized, getsubopt() returns the index of the matching suboption element in tokens. Otherwise, -1 is returned and *valuepis the entire name[=value]string.

Since *optionpis changed, the first suboption before the call to getsubopt() is not (necessarily) the same as the first suboption after getsubopt().  

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
getsubopt() Thread safetyMT-Safe
 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008.  

NOTES

Since getsubopt() overwrites any commas it finds in the string *optionp, that string must be writable; it cannot be a string constant.  

EXAMPLE

The following program expects suboptions following a "-o" option.

#define _XOPEN_SOURCE 500
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>

int
main(int argc, char **argv)
{
    enum {
        RO_OPT = 0,
        RW_OPT,
        NAME_OPT
    };
    char *const token[] = {
        [RO_OPT]   = "ro",
        [RW_OPT]   = "rw",
        [NAME_OPT] = "name",
        NULL
    };
    char *subopts;
    char *value;
    int opt;

    int readonly = 0;
    int readwrite = 0;
    char *name = NULL;
    int errfnd = 0;

    while ((opt = getopt(argc, argv, "o:")) != -1) {
        switch (opt) {
        case aqoaq:
            subopts = optarg;
            while (*subopts != aq\0aq && !errfnd) {

            switch (getsubopt(&subopts, token, &value)) {
            case RO_OPT:
                readonly = 1;
                break;

            case RW_OPT:
                readwrite = 1;
                break;

            case NAME_OPT:
                if (value == NULL) {
                    fprintf(stderr, "Missing value for "
                            "suboption aq%saq\n", token[NAME_OPT]);
                    errfnd = 1;
                    continue;
                }

                name = value;
                break;

            default:
                fprintf(stderr, "No match found "
                        "for token: /%s/\n", value);
                errfnd = 1;
                break;
            }
        }
        if (readwrite && readonly) {
            fprintf(stderr, "Only one of aq%saq and aq%saq can be "
                    "specified\n", token[RO_OPT], token[RW_OPT]);
            errfnd = 1;
        }
        break;

        default:
            errfnd = 1;
        }
    }

    if (errfnd || argc == 1) {
        fprintf(stderr, "\nUsage: %s -o <suboptstring>\n", argv[0]);
        fprintf(stderr, "suboptions are aqroaq, aqrwaq, "
                "and aqname=<value>aq\n");
        exit(EXIT_FAILURE);
    }

    /* Remainder of program... */

    exit(EXIT_SUCCESS);
}
 

SEE ALSO

getopt(3)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ATTRIBUTES
CONFORMING TO
NOTES
EXAMPLE
SEE ALSO

This document was created by man2html, using the manual pages.
Time: 16:30:21 GMT, October 09, 2016 Click Here!