|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
|
|
|
getsubopt(3) Library Functions Manual getsubopt(3)
getsubopt - parse suboption arguments from a string
Standard C library (libc, -lc)
#include <stdlib.h>
int getsubopt(char **restrict optionp, char *const *restrict tokens,
char **restrict valuep);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getsubopt():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
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 tokens argument 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 *valuep to the address of
that string. The first comma in optionp is overwritten with a
null byte, so *valuep is precisely the "value string" for that
suboption.
If the suboption is recognized, but no value string was found,
*valuep is set to NULL.
When getsubopt() returns, optionp points to the next suboption, or
to the null byte ('\0') at the end of the string if the last
suboption was just processed.
If the first suboption in optionp is recognized, getsubopt()
returns the index of the matching suboption element in tokens.
Otherwise, -1 is returned and *valuep is the entire name[=value]
string.
Since *optionp is changed, the first suboption before the call to
getsubopt() is not (necessarily) the same as the first suboption
after getsubopt().
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ getsubopt() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
POSIX.1-2001.
Since getsubopt() overwrites any commas it finds in the string
*optionp, that string must be writable; it cannot be a string
constant.
The following program expects suboptions following a "-o" option.
#define _XOPEN_SOURCE 500
#include <stdio.h>
#include <stdlib.h>
#include <assert.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 'o':
subopts = optarg;
while (*subopts != '\0' && !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 '%s'\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 '%s' and '%s' 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 'ro', 'rw', and 'name=<value>'\n");
exit(EXIT_FAILURE);
}
/* Remainder of program... */
exit(EXIT_SUCCESS);
}
getopt(3)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 getsubopt(3)
Pages that refer to this page: getopt(3)
Copyright and license for this manual page
|
HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|