1GETSUBOPT(3)               Linux Programmer's Manual              GETSUBOPT(3)
2
3
4

NAME

6       getsubopt - parse suboption arguments from a string
7

SYNOPSIS

9       #include <stdlib.h>
10
11       int getsubopt(char **optionp, char * const *tokens, char **valuep);
12
13   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
14
15       getsubopt():
16           _XOPEN_SOURCE >= 500
17               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
18

DESCRIPTION

20       getsubopt()  parses  the list of comma-separated suboptions provided in
21       optionp.  (Such a suboption list is typically produced  when  getopt(3)
22       is  used  to  parse  a  command  line; see for example the -o option of
23       mount(8).)  Each suboption may include an associated  value,  which  is
24       separated  from  the suboption name by an equal sign.  The following is
25       an example of the kind of string that might be passed in optionp:
26
27           ro,name=xyz
28
29       The tokens argument is a pointer to a NULL-terminated array of pointers
30       to  the  tokens  that getsubopt() will look for in optionp.  The tokens
31       should be distinct, null-terminated strings  containing  at  least  one
32       character, with no embedded equal signs or commas.
33
34       Each call to getsubopt() returns information about the next unprocessed
35       suboption in optionp.  The first equal sign in a suboption (if any)  is
36       interpreted  as a separator between the name and the value of that sub‐
37       option.  The value extends to the next comma, or (for the  last  subop‐
38       tion) to the end of the string.  If the name of the suboption matches a
39       known name from tokens, and a value string was found, getsubopt()  sets
40       *valuep  to  the address of that string.  The first comma in optionp is
41       overwritten with a null  byte,  so  *valuep  is  precisely  the  "value
42       string" for that suboption.
43
44       If  the suboption is recognized, but no value string was found, *valuep
45       is set to NULL.
46
47       When getsubopt() returns, optionp points to the next suboption,  or  to
48       the null byte ('\0') at the end of the string if the last suboption was
49       just processed.
50

RETURN VALUE

52       If the first suboption in optionp is  recognized,  getsubopt()  returns
53       the  index  of the matching suboption element in tokens.  Otherwise, -1
54       is returned and *valuep is the entire name[=value] string.
55
56       Since *optionp is changed, the first suboption before the call to  get‐
57       subopt()  is  not  (necessarily)  the same as the first suboption after
58       getsubopt().
59

ATTRIBUTES

61       For  an  explanation  of  the  terms  used   in   this   section,   see
62       attributes(7).
63
64       ┌────────────┬───────────────┬─────────┐
65Interface   Attribute     Value   
66       ├────────────┼───────────────┼─────────┤
67getsubopt() │ Thread safety │ MT-Safe │
68       └────────────┴───────────────┴─────────┘

CONFORMING TO

70       POSIX.1-2001, POSIX.1-2008.
71

NOTES

73       Since  getsubopt()  overwrites  any  commas  it  finds  in  the  string
74       *optionp, that string must be writable; it cannot be a string constant.
75

EXAMPLE

77       The following program expects suboptions following a "-o" option.
78
79       #define _XOPEN_SOURCE 500
80       #include <stdlib.h>
81       #include <assert.h>
82       #include <stdio.h>
83
84       int
85       main(int argc, char **argv)
86       {
87           enum {
88               RO_OPT = 0,
89               RW_OPT,
90               NAME_OPT
91           };
92           char *const token[] = {
93               [RO_OPT]   = "ro",
94               [RW_OPT]   = "rw",
95               [NAME_OPT] = "name",
96               NULL
97           };
98           char *subopts;
99           char *value;
100           int opt;
101
102           int readonly = 0;
103           int readwrite = 0;
104           char *name = NULL;
105           int errfnd = 0;
106
107           while ((opt = getopt(argc, argv, "o:")) != -1) {
108               switch (opt) {
109               case 'o':
110                   subopts = optarg;
111                   while (*subopts != '\0' && !errfnd) {
112
113                   switch (getsubopt(&subopts, token, &value)) {
114                   case RO_OPT:
115                       readonly = 1;
116                       break;
117
118                   case RW_OPT:
119                       readwrite = 1;
120                       break;
121
122                   case NAME_OPT:
123                       if (value == NULL) {
124                           fprintf(stderr, "Missing value for "
125                                   "suboption '%s'\n", token[NAME_OPT]);
126                           errfnd = 1;
127                           continue;
128                       }
129
130                       name = value;
131                       break;
132
133                   default:
134                       fprintf(stderr, "No match found "
135                               "for token: /%s/\n", value);
136                       errfnd = 1;
137                       break;
138                   }
139               }
140               if (readwrite && readonly) {
141                   fprintf(stderr, "Only one of '%s' and '%s' can be "
142                           "specified\n", token[RO_OPT], token[RW_OPT]);
143                   errfnd = 1;
144               }
145               break;
146
147               default:
148                   errfnd = 1;
149               }
150           }
151
152           if (errfnd || argc == 1) {
153               fprintf(stderr, "\nUsage: %s -o <suboptstring>\n", argv[0]);
154               fprintf(stderr, "suboptions are 'ro', 'rw', "
155                       "and 'name=<value>'\n");
156               exit(EXIT_FAILURE);
157           }
158
159           /* Remainder of program... */
160
161           exit(EXIT_SUCCESS);
162       }
163

SEE ALSO

165       getopt(3)
166

COLOPHON

168       This page is part of release 5.04 of the Linux  man-pages  project.   A
169       description  of  the project, information about reporting bugs, and the
170       latest    version    of    this    page,    can     be     found     at
171       https://www.kernel.org/doc/man-pages/.
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175GNU                               2019-03-06                      GETSUBOPT(3)
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