man3/getsubopt.3

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  25 .TH getsubopt 3 (date) "Linux man-pages (unreleased)"
  26 .SH NAME
  27 getsubopt \- parse suboption arguments from a string
  28 .SH LIBRARY
  29 Standard C library
  30 .RI ( libc ", " \-lc )
  31 .SH SYNOPSIS
  32 .nf
  33 .B #include <stdlib.h>
  34 .PP
  35 .BI "int getsubopt(char **restrict " optionp ", char *const *restrict " tokens ,
  36 .BI "              char **restrict " valuep );
  37 .fi
  38 .PP
  39 .RS -4
  40 Feature Test Macro Requirements for glibc (see
  41 .BR feature_test_macros (7)):
  42 .RE
  43 .PP
  44 .BR getsubopt ():
  45 .nf
  46     _XOPEN_SOURCE >= 500
  47 .\"    || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
  48         || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
  49 .fi
  50 .SH DESCRIPTION
  51 .BR getsubopt ()
  52 parses the list of comma-separated suboptions provided in
  53 .IR optionp .
  54 (Such a suboption list is typically produced when
  55 .BR getopt (3)
  56 is used to parse a command line;
  57 see for example the \fI\-o\fP option of
  58 .BR mount (8).)
  59 Each suboption may include an associated value,
  60 which is separated from the suboption name by an equal sign.
  61 The following is an example of the kind of string
  62 that might be passed in
  63 .IR optionp :
  64 .PP
  65 .in +4n
  66 .EX
  67 .B ro,name=xyz
  68 .EE
  69 .in
  70 .PP
  71 The
  72 .I tokens
  73 argument is a pointer to a NULL-terminated array of pointers to the tokens that
  74 .BR getsubopt ()
  75 will look for in
  76 .IR optionp .
  77 The tokens should be distinct, null-terminated strings containing at
  78 least one character, with no embedded equal signs or commas.
  79 .PP
  80 Each call to
  81 .BR getsubopt ()
  82 returns information about the next unprocessed suboption in
  83 .IR optionp .
  84 The first equal sign in a suboption (if any) is interpreted as a
  85 separator between the name and the value of that suboption.
  86 The value extends to the next comma,
  87 or (for the last suboption) to the end of the string.
  88 If the name of the suboption matches a known name from
  89 .IR tokens ,
  90 and a value string was found,
  91 .BR getsubopt ()
  92 sets
  93 .I *valuep
  94 to the address of that string.
  95 The first comma in
  96 .I optionp
  97 is overwritten with a null byte, so
  98 .I *valuep
  99 is precisely the "value string" for that suboption.
 100 .PP
 101 If the suboption is recognized, but no value string was found,
 102 .I *valuep
 103 is set to NULL.
 104 .PP
 105 When
 106 .BR getsubopt ()
 107 returns,
 108 .I optionp
 109 points to the next suboption,
 110 or to the null byte (\(aq\e0\(aq) at the end of the
 111 string if the last suboption was just processed.
 112 .SH RETURN VALUE
 113 If the first suboption in
 114 .I optionp
 115 is recognized,
 116 .BR getsubopt ()
 117 returns the index of the matching suboption element in
 118 .IR tokens .
 119 Otherwise, \-1 is returned and
 120 .I *valuep
 121 is the entire
 122 .IB name [= value ]
 123 string.
 124 .PP
 125 Since
 126 .I *optionp
 127 is changed, the first suboption before the call to
 128 .BR getsubopt ()
 129 is not (necessarily) the same as the first suboption after
 130 .BR getsubopt ().
 131 .SH ATTRIBUTES
 132 For an explanation of the terms used in this section, see
 133 .BR attributes (7).
 134 .ad l
 135 .nh
 136 .TS
 137 allbox;
 138 lbx lb lb
 139 l l l.
 140 Interface       Attribute       Value
 141 T{
 142 .BR getsubopt ()
 143 T}      Thread safety   MT-Safe
 144 .TE
 145 .hy
 146 .ad
 147 .sp 1
 148 .SH STANDARDS
 149 POSIX.1-2001, POSIX.1-2008.
 150 .SH NOTES
 151 Since
 152 .BR getsubopt ()
 153 overwrites any commas it finds in the string
 154 .IR *optionp ,
 155 that string must be writable; it cannot be a string constant.
 156 .SH EXAMPLES
 157 The following program expects suboptions following a "\-o" option.
 158 .PP
 159 .\" SRC BEGIN (getsubopt.c)
 160 .EX
 161 #define _XOPEN_SOURCE 500
 162 #include <stdio.h>
 163 #include <stdlib.h>
 164
 165 #include <assert.h>
 166
 167 int
 168 main(int argc, char *argv[])
 169 {
 170     enum {
 171         RO_OPT = 0,
 172         RW_OPT,
 173         NAME_OPT
 174     };
 175     char *const token[] = {
 176         [RO_OPT]   = "ro",
 177         [RW_OPT]   = "rw",
 178         [NAME_OPT] = "name",
 179         NULL
 180     };
 181     char *subopts;
 182     char *value;
 183     int opt;
 184
 185     int readonly = 0;
 186     int readwrite = 0;
 187     char *name = NULL;
 188     int errfnd = 0;
 189
 190     while ((opt = getopt(argc, argv, "o:")) != \-1) {
 191         switch (opt) {
 192         case \(aqo\(aq:
 193             subopts = optarg;
 194             while (*subopts != \(aq\e0\(aq && !errfnd) {
 195
 196                 switch (getsubopt(&subopts, token, &value)) {
 197                 case RO_OPT:
 198                     readonly = 1;
 199                     break;
 200
 201                 case RW_OPT:
 202                     readwrite = 1;
 203                     break;
 204
 205                 case NAME_OPT:
 206                     if (value == NULL) {
 207                         fprintf(stderr,
 208                                 "Missing value for suboption \(aq%s\(aq\en",
 209                                 token[NAME_OPT]);
 210                         errfnd = 1;
 211                         continue;
 212                     }
 213
 214                     name = value;
 215                     break;
 216
 217                 default:
 218                     fprintf(stderr,
 219                             "No match found for token: /%s/\en", value);
 220                     errfnd = 1;
 221                     break;
 222                 }
 223             }
 224             if (readwrite && readonly) {
 225                 fprintf(stderr,
 226                         "Only one of \(aq%s\(aq and \(aq%s\(aq can be specified\en",
 227                         token[RO_OPT], token[RW_OPT]);
 228                 errfnd = 1;
 229             }
 230             break;
 231
 232         default:
 233             errfnd = 1;
 234         }
 235     }
 236
 237     if (errfnd || argc == 1) {
 238         fprintf(stderr, "\enUsage: %s \-o <suboptstring>\en", argv[0]);
 239         fprintf(stderr,
 240                 "suboptions are \(aqro\(aq, \(aqrw\(aq, and \(aqname=<value>\(aq\en");
 241         exit(EXIT_FAILURE);
 242     }
 243
 244     /* Remainder of program... */
 245
 246     exit(EXIT_SUCCESS);
 247 }
 248 .EE
 249 .\" SRC END
 250 .SH SEE ALSO
 251 .BR getopt (3)