man3/getsubopt.3

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  25 .TH GETSUBOPT 3 2017-09-15 "GNU" "Linux Programmer's Manual"
  26 .SH NAME
  27 getsubopt \- parse suboption arguments from a string
  28 .SH SYNOPSIS
  29 .B #include <stdlib.h>
  30 .PP
  31 .BI "int getsubopt(char **"optionp ", char * const *" tokens \
  32 ", char **" valuep );
  33 .PP
  34 .in -4n
  35 Feature Test Macro Requirements for glibc (see
  36 .BR feature_test_macros (7)):
  37 .in
  38 .PP
  39 .BR getsubopt ():
  40 .ad l
  41 .RS 4
  42 .PD 0
  43 _XOPEN_SOURCE\ >= 500
  44 .\"    || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  45 .br
  46     || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
  47 .PD
  48 .RE
  49 .ad
  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\\0\(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 .TS
 135 allbox;
 136 lb lb lb
 137 l l l.
 138 Interface       Attribute       Value
 139 T{
 140 .BR getsubopt ()
 141 T}      Thread safety   MT-Safe
 142 .TE
 143 .SH CONFORMING TO
 144 POSIX.1-2001, POSIX.1-2008.
 145 .SH NOTES
 146 .PP
 147 Since
 148 .BR getsubopt ()
 149 overwrites any commas it finds in the string
 150 .IR *optionp ,
 151 that string must be writable; it cannot be a string constant.
 152 .SH EXAMPLE
 153 The following program expects suboptions following a "\-o" option.
 154 .PP
 155 .EX
 156 #define _XOPEN_SOURCE 500
 157 #include <stdlib.h>
 158 #include <assert.h>
 159 #include <stdio.h>
 160
 161 int
 162 main(int argc, char **argv)
 163 {
 164     enum {
 165         RO_OPT = 0,
 166         RW_OPT,
 167         NAME_OPT
 168     };
 169     char *const token[] = {
 170         [RO_OPT]   = "ro",
 171         [RW_OPT]   = "rw",
 172         [NAME_OPT] = "name",
 173         NULL
 174     };
 175     char *subopts;
 176     char *value;
 177     int opt;
 178
 179     int readonly = 0;
 180     int readwrite = 0;
 181     char *name = NULL;
 182     int errfnd = 0;
 183
 184     while ((opt = getopt(argc, argv, "o:")) != \-1) {
 185         switch (opt) {
 186         case \(aqo\(aq:
 187             subopts = optarg;
 188             while (*subopts != \(aq\\0\(aq && !errfnd) {
 189
 190             switch (getsubopt(&subopts, token, &value)) {
 191             case RO_OPT:
 192                 readonly = 1;
 193                 break;
 194
 195             case RW_OPT:
 196                 readwrite = 1;
 197                 break;
 198
 199             case NAME_OPT:
 200                 if (value == NULL) {
 201                     fprintf(stderr, "Missing value for "
 202                             "suboption \(aq%s\(aq\\n", token[NAME_OPT]);
 203                     errfnd = 1;
 204                     continue;
 205                 }
 206
 207                 name = value;
 208                 break;
 209
 210             default:
 211                 fprintf(stderr, "No match found "
 212                         "for token: /%s/\\n", value);
 213                 errfnd = 1;
 214                 break;
 215             }
 216         }
 217         if (readwrite && readonly) {
 218             fprintf(stderr, "Only one of \(aq%s\(aq and \(aq%s\(aq can be "
 219                     "specified\\n", token[RO_OPT], token[RW_OPT]);
 220             errfnd = 1;
 221         }
 222         break;
 223
 224         default:
 225             errfnd = 1;
 226         }
 227     }
 228
 229     if (errfnd || argc == 1) {
 230         fprintf(stderr, "\\nUsage: %s \-o <suboptstring>\\n", argv[0]);
 231         fprintf(stderr, "suboptions are \(aqro\(aq, \(aqrw\(aq, "
 232                 "and \(aqname=<value>\(aq\\n");
 233         exit(EXIT_FAILURE);
 234     }
 235
 236     /* Remainder of program... */
 237
 238     exit(EXIT_SUCCESS);
 239 }
 240 .EE
 241 .SH SEE ALSO
 242 .BR getopt (3)