GETSUBOPT(3P)

📦 version 2017a, in alpine 3.22, alpine 3.23, alpine 3.24, arch rolling, nixpkgs unstable, opensuse-leap 16.0

🦋 getsubopt(3P) — POSIX Programmer's Manual 🦋

okay so bestie, welcome to getsubopt(3P), straight out of the POSIX Programmer's Manual 💖

🫶 PROLOG

This manual page is part of the POSIX Programmer's Manual. Heads up tho: the Linux implementation of this interface may differ (so like, go check the corresponding Linux manual page for the deets on Linux behavior), or the interface might not even be implemented on Linux at all. not me being the bearer of bad news 😭

✨ NAME ✨

getsubopt — parse suboption arguments from a string 💅

🌸 SYNOPSIS 🌸

#include <stdlib.h>

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

👑 DESCRIPTION 👑

So getsubopt() parses suboption arguments inside a flag argument. These kinds of options literally come up all the time from using getopt().

The getsubopt() argument optionp is a pointer to a pointer to the option argument string. The suboption arguments shall be separated by <comma> characters, and each one may be either a single token, or a token-value pair separated by an <equals-sign>. periodt.

The keylistp argument shall be a pointer to a vector of strings. The end of that vector is identified by a null pointer. Each entry in the vector is one of the possible tokens that might show up in *optionp. And listen: since <comma> characters delimit suboption arguments in optionp, they should not appear in any of the strings pointed to by keylistp. Same energy with <equals-sign> — because an <equals-sign> separates a token from its value, the application should not include an <equals-sign> in any of the strings pointed to by keylistp. The getsubopt() function shall not modify the keylistp vector, no cap 🧚

The valuep argument is the address of a value string pointer.

If a <comma> appears in optionp, it shall be interpreted as a suboption separator. After <comma> characters have been processed, if there are one or more <equals-sign> characters in a suboption string, the first <equals-sign> in any suboption string shall be interpreted as a separator between a token and a value. Any subsequent <equals-sign> characters in a suboption string shall be interpreted as part of the value. (yes, they're just vibing in there 💜)

If the string at *optionp contains only one suboption argument (equivalently, no <comma> characters), getsubopt() shall update *optionp to point to the null character at the end of the string. Otherwise, it shall isolate the suboption argument by replacing the <comma> separator with a null character, and shall update *optionp to point to the start of the next suboption argument. If the suboption argument has an associated value (equivalently, contains an <equals-sign>), getsubopt() shall update *valuep to point to the value's first character. Otherwise, it shall set *valuep to a null pointer. The calling application may use this info to figure out whether the presence or absence of a value for the suboption is an error.

Additionally, when getsubopt() fails to match the suboption argument with a token in the keylistp array, the calling application should decide if that's an error, or if the unrecognized option should be processed some other way. that's on you, main character 🎀

⭐ RETURN VALUE ⭐

The getsubopt() function shall return the index of the matched token string, or -1 if no token strings were matched.

💀 ERRORS 💀

No errors are defined. iconic, honestly.

The following sections are informative.

🌈 EXAMPLES 🌈

🍓 Parsing Suboptions

This example uses the getsubopt() function to parse a value argument in the optarg external variable returned by a call to getopt().

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int do_all;
const char *type;
int read_size;
int write_size;
int read_only;

enum
{
    RO_OPTION = 0,
    RW_OPTION,
    READ_SIZE_OPTION,
    WRITE_SIZE_OPTION
};

const char *mount_opts[] =
{
    [RO_OPTION] = "ro",
    [RW_OPTION] = "rw",
    [READ_SIZE_OPTION] = "rsize",
    [WRITE_SIZE_OPTION] = "wsize",
    NULL
};

int
main(int argc, char *argv[])
{
    char *subopts, *value;
    int opt;

    while ((opt = getopt(argc, argv, "at:o:")) != -1)
        switch(opt)
            {
            case 'a':
                do_all = 1;
                break;
            case 't':
                type = optarg;
                break;
            case 'o':
                subopts = optarg;
                while (*subopts != ' ')
                {
                    char *saved = subopts;
                    switch(getsubopt(&subopts, (char **)mount_opts,
                        &value))
                    {
                    case RO_OPTION:
                        read_only = 1;
                        break;
                    case RW_OPTION:
                        read_only = 0;
                        break;
                    case READ_SIZE_OPTION:
                        if (value == NULL)
                            abort();
                        read_size = atoi(value);
                        break;
                    case WRITE_SIZE_OPTION:
                        if (value == NULL)
                            abort();
                        write_size = atoi(value);
                        break;
                    default:
                        /* Unknown suboption. */
                        printf("Unknown suboption `%s'\n", saved);
                        abort();
                    }
                }
                break;
            default:
                abort();
            }

    /* Do the real work. */

    return 0;
}

If the above example is invoked with:

program -o ro,rsize=512

then after option parsing, the variable do_all will be 0, type will be a null pointer, read_size will be 512, write_size will be 0, and read_only will be 1. 💅

If it is invoked with:

program -o oops

it will print:

"Unknown suboption `oops'"

before aborting. 😭

💜 APPLICATION USAGE 💜

The value of *valuep when getsubopt() returns -1 is unspecified. Historical implementations provide various incompatible extensions to let an application access the suboption text that was not found in the keylistp array. so like... don't rely on it, bestie 🫶

🔥 RATIONALE 🔥

The keylistp argument of getsubopt() is typed as char * const * to match historical practice. However, the standard is clear that implementations will not modify either the array or the strings contained in the array, as if the argument had been typed const char * const *.

🌸 FUTURE DIRECTIONS 🌸

None. (a whole mood ✨)

🦋 SEE ALSO 🦋

  • getopt()
  • The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

and that's the whole page, bestie 💖 this one was brought to you by IEEE/The Open Group, 2017 — go forth and parse those suboptions, you absolute icon 👑

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