1GETSUBOPT(3) Linux Programmer's Manual GETSUBOPT(3)
2
6 getsubopt - parse suboption arguments from a string
7
9 #include <stdlib.h>
10 int getsubopt(char **restrict optionp, char *const *restrict tokens,
12 char **restrict valuep);
13 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
15 getsubopt():
17 _XOPEN_SOURCE >= 500
18 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
19
21 getsubopt() parses the list of comma-separated suboptions provided in
22 optionp. (Such a suboption list is typically produced when getopt(3)
23 is used to parse a command line; see for example the -o option of
24 mount(8).) Each suboption may include an associated value, which is
25 separated from the suboption name by an equal sign. The following is
26 an example of the kind of string that might be passed in optionp:
27 ro,name=xyz
29 The tokens argument is a pointer to a NULL-terminated array of pointers
31 to the tokens that getsubopt() will look for in optionp. The tokens
32 should be distinct, null-terminated strings containing at least one
33 character, with no embedded equal signs or commas.
34 Each call to getsubopt() returns information about the next unprocessed
36 suboption in optionp. The first equal sign in a suboption (if any) is
37 interpreted as a separator between the name and the value of that sub‐
38 option. The value extends to the next comma, or (for the last subop‐
39 tion) to the end of the string. If the name of the suboption matches a
40 known name from tokens, and a value string was found, getsubopt() sets
41 *valuep to the address of that string. The first comma in optionp is
42 overwritten with a null byte, so *valuep is precisely the "value
43 string" for that suboption.
44 If the suboption is recognized, but no value string was found, *valuep
46 is set to NULL.
47 When getsubopt() returns, optionp points to the next suboption, or to
49 the null byte ('\0') at the end of the string if the last suboption was
50 just processed.
51
53 If the first suboption in optionp is recognized, getsubopt() returns
54 the index of the matching suboption element in tokens. Otherwise, -1
55 is returned and *valuep is the entire name[=value] string.
56 Since *optionp is changed, the first suboption before the call to get‐
58 subopt() is not (necessarily) the same as the first suboption after
59 getsubopt().
60
62 For an explanation of the terms used in this section, see at‐
63 tributes(7).
64 ┌────────────────────────────────────────────┬───────────────┬─────────┐
66 │Interface │ Attribute │ Value │
67 ├────────────────────────────────────────────┼───────────────┼─────────┤
68 │getsubopt() │ Thread safety │ MT-Safe │
69 └────────────────────────────────────────────┴───────────────┴─────────┘
70
72 POSIX.1-2001, POSIX.1-2008.
73
75 Since getsubopt() overwrites any commas it finds in the string *op‐
76 tionp, that string must be writable; it cannot be a string constant.
77
79 The following program expects suboptions following a "-o" option.
80 #define _XOPEN_SOURCE 500
82 #include <stdlib.h>
83 #include <assert.h>
84 #include <stdio.h>
85 int
87 main(int argc, char *argv[])
88 {
89 enum {
90 RO_OPT = 0,
91 RW_OPT,
92 NAME_OPT
93 };
94 char *const token[] = {
95 [RO_OPT] = "ro",
96 [RW_OPT] = "rw",
97 [NAME_OPT] = "name",
98 NULL
99 };
100 char *subopts;
101 char *value;
102 int opt;
103 int readonly = 0;
105 int readwrite = 0;
106 char *name = NULL;
107 int errfnd = 0;
108 while ((opt = getopt(argc, argv, "o:")) != -1) {
110 switch (opt) {
111 case 'o':
112 subopts = optarg;
113 while (*subopts != '\0' && !errfnd) {
114 switch (getsubopt(&subopts, token, &value)) {
116 case RO_OPT:
117 readonly = 1;
118 break;
119 case RW_OPT:
121 readwrite = 1;
122 break;
123 case NAME_OPT:
125 if (value == NULL) {
126 fprintf(stderr, "Missing value for "
127 "suboption '%s'\n", token[NAME_OPT]);
128 errfnd = 1;
129 continue;
130 }
131 name = value;
133 break;
134 default:
136 fprintf(stderr, "No match found "
137 "for token: /%s/\n", value);
138 errfnd = 1;
139 break;
140 }
141 }
142 if (readwrite && readonly) {
143 fprintf(stderr, "Only one of '%s' and '%s' can be "
144 "specified\n", token[RO_OPT], token[RW_OPT]);
145 errfnd = 1;
146 }
147 break;
148 default:
150 errfnd = 1;
151 }
152 }
153 if (errfnd || argc == 1) {
155 fprintf(stderr, "\nUsage: %s -o <suboptstring>\n", argv[0]);
156 fprintf(stderr, "suboptions are 'ro', 'rw', "
157 "and 'name=<value>'\n");
158 exit(EXIT_FAILURE);
159 }
160 /* Remainder of program... */
162 exit(EXIT_SUCCESS);
164 }
165
167 getopt(3)
168
170 This page is part of release 5.13 of the Linux man-pages project. A
171 description of the project, information about reporting bugs, and the
172 latest version of this page, can be found at
173 https://www.kernel.org/doc/man-pages/.
174GNU 2021-08-27 GETSUBOPT(3)