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 .ad l
 136 .nh
 137 .TS
 138 allbox;
 139 lbx lb lb
 140 l l l.
 141 Interface       Attribute       Value
 142 T{
 143 .BR getsubopt ()
 144 T}      Thread safety   MT-Safe
 145 .TE
 146 .hy
 147 .ad
 148 .sp 1
 149 .SH STANDARDS
 150 POSIX.1-2008.
 151 .SH HISTORY
 152 POSIX.1-2001.
 153 .SH NOTES
 154 Since
 155 .BR getsubopt ()
 156 overwrites any commas it finds in the string
 157 .IR *optionp ,
 158 that string must be writable; it cannot be a string constant.
 159 .SH EXAMPLES
 160 The following program expects suboptions following a "\-o" option.
 161 .PP
 162 .\" SRC BEGIN (getsubopt.c)
 163 .EX
 164 #define _XOPEN_SOURCE 500
 165 #include <stdio.h>
 166 #include <stdlib.h>
 167 \&
 168 #include <assert.h>
 169 \&
 170 int
 171 main(int argc, char *argv[])
 172 {
 173     enum {
 174         RO_OPT = 0,
 175         RW_OPT,
 176         NAME_OPT
 177     };
 178     char *const token[] = {
 179         [RO_OPT]   = "ro",
 180         [RW_OPT]   = "rw",
 181         [NAME_OPT] = "name",
 182         NULL
 183     };
 184     char *subopts;
 185     char *value;
 186     int opt;
 187 \&
 188     int readonly = 0;
 189     int readwrite = 0;
 190     char *name = NULL;
 191     int errfnd = 0;
 192 \&
 193     while ((opt = getopt(argc, argv, "o:")) != \-1) {
 194         switch (opt) {
 195         case \[aq]o\[aq]:
 196             subopts = optarg;
 197             while (*subopts != \[aq]\e0\[aq] && !errfnd) {
 198 \&
 199                 switch (getsubopt(&subopts, token, &value)) {
 200                 case RO_OPT:
 201                     readonly = 1;
 202                     break;
 203 \&
 204                 case RW_OPT:
 205                     readwrite = 1;
 206                     break;
 207 \&
 208                 case NAME_OPT:
 209                     if (value == NULL) {
 210                         fprintf(stderr,
 211                                 "Missing value for suboption \[aq]%s\[aq]\en",
 212                                 token[NAME_OPT]);
 213                         errfnd = 1;
 214                         continue;
 215                     }
 216 \&
 217                     name = value;
 218                     break;
 219 \&
 220                 default:
 221                     fprintf(stderr,
 222                             "No match found for token: /%s/\en", value);
 223                     errfnd = 1;
 224                     break;
 225                 }
 226             }
 227             if (readwrite && readonly) {
 228                 fprintf(stderr,
 229                         "Only one of \[aq]%s\[aq] and \[aq]%s\[aq] can be specified\en",
 230                         token[RO_OPT], token[RW_OPT]);
 231                 errfnd = 1;
 232             }
 233             break;
 234 \&
 235         default:
 236             errfnd = 1;
 237         }
 238     }
 239 \&
 240     if (errfnd || argc == 1) {
 241         fprintf(stderr, "\enUsage: %s \-o <suboptstring>\en", argv[0]);
 242         fprintf(stderr,
 243                 "suboptions are \[aq]ro\[aq], \[aq]rw\[aq], and \[aq]name=<value>\[aq]\en");
 244         exit(EXIT_FAILURE);
 245     }
 246 \&
 247     /* Remainder of program... */
 248 \&
 249     exit(EXIT_SUCCESS);
 250 }
 251 .EE
 252 .\" SRC END
 253 .SH SEE ALSO
 254 .BR getopt (3)