path: root/man3/getsubopt.3

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.TH getsubopt 3 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
getsubopt \- parse suboption arguments from a string
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "int getsubopt(char **restrict " optionp ", char *const *restrict " tokens ,
.BI "              char **restrict " valuep );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR getsubopt ():
.nf
    _XOPEN_SOURCE >= 500
.\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
        || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
.fi
.SH DESCRIPTION
.BR getsubopt ()
parses the list of comma-separated suboptions provided in
.IR optionp .
(Such a suboption list is typically produced when
.BR getopt (3)
is used to parse a command line;
see for example the \fI\-o\fP option of
.BR 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
.IR optionp :
.PP
.in +4n
.EX
.B ro,name=xyz
.EE
.in
.PP
The
.I tokens
argument is a pointer to a NULL-terminated array of pointers to the tokens that
.BR getsubopt ()
will look for in
.IR optionp .
The tokens should be distinct, null-terminated strings containing at
least one character, with no embedded equal signs or commas.
.PP
Each call to
.BR getsubopt ()
returns information about the next unprocessed suboption in
.IR 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
.IR tokens ,
and a value string was found,
.BR getsubopt ()
sets
.I *valuep
to the address of that string.
The first comma in
.I optionp
is overwritten with a null byte, so
.I *valuep
is precisely the "value string" for that suboption.
.PP
If the suboption is recognized, but no value string was found,
.I *valuep
is set to NULL.
.PP
When
.BR getsubopt ()
returns,
.I optionp
points to the next suboption,
or to the null byte (\[aq]\e0\[aq]) at the end of the
string if the last suboption was just processed.
.SH RETURN VALUE
If the first suboption in
.I optionp
is recognized,
.BR getsubopt ()
returns the index of the matching suboption element in
.IR tokens .
Otherwise, \-1 is returned and
.I *valuep
is the entire
.IB name [= value ]
string.
.PP
Since
.I *optionp
is changed, the first suboption before the call to
.BR getsubopt ()
is not (necessarily) the same as the first suboption after
.BR getsubopt ().
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR getsubopt ()
T}	Thread safety	MT-Safe
.TE
.sp 1
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
POSIX.1-2001.
.SH NOTES
Since
.BR getsubopt ()
overwrites any commas it finds in the string
.IR *optionp ,
that string must be writable; it cannot be a string constant.
.SH EXAMPLES
The following program expects suboptions following a "\-o" option.
.PP
.\" SRC BEGIN (getsubopt.c)
.EX
#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 \[aq]o\[aq]:
            subopts = optarg;
            while (*subopts != \[aq]\e0\[aq] && !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]%s\[aq]\en",
                                token[NAME_OPT]);
                        errfnd = 1;
                        continue;
                    }
\&
                    name = value;
                    break;
\&
                default:
                    fprintf(stderr,
                            "No match found for token: /%s/\en", value);
                    errfnd = 1;
                    break;
                }
            }
            if (readwrite && readonly) {
                fprintf(stderr,
                        "Only one of \[aq]%s\[aq] and \[aq]%s\[aq] can be specified\en",
                        token[RO_OPT], token[RW_OPT]);
                errfnd = 1;
            }
            break;
\&
        default:
            errfnd = 1;
        }
    }
\&
    if (errfnd || argc == 1) {
        fprintf(stderr, "\enUsage: %s \-o <suboptstring>\en", argv[0]);
        fprintf(stderr,
                "suboptions are \[aq]ro\[aq], \[aq]rw\[aq], and \[aq]name=<value>\[aq]\en");
        exit(EXIT_FAILURE);
    }
\&
    /* Remainder of program... */
\&
    exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR getopt (3)