man3/getsubopt.3

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