man3/getsubopt.3

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  23 .TH GETSUBOPT 3 2010-09-26 "GNU" "Linux Programmer's Manual"
  24 .SH NAME
  25 getsubopt \- parse suboption arguments from a string
  26 .SH SYNOPSIS
  27 .B #include <stdlib.h>
  28
  29 .BI "int getsubopt(char **"optionp ", char * const *" tokens \
  30 ", char **" valuep );
  31 .sp
  32 .in -4n
  33 Feature Test Macro Requirements for glibc (see
  34 .BR feature_test_macros (7)):
  35 .in
  36 .sp
  37 .BR getsubopt ():
  38 .ad l
  39 .RS 4
  40 .PD 0
  41 _XOPEN_SOURCE\ >= 500 ||
  42 _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
  43 .br
  44 || /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
  45 .PD
  46 .RE
  47 .ad
  48 .SH DESCRIPTION
  49 .BR getsubopt ()
  50 parses the list of comma-separated suboptions provided in
  51 .IR optionp .
  52 (Such a suboption list is typically produced when
  53 .BR getopt (3)
  54 is used to parse a command line;
  55 see for example the \fI-o\fP option of
  56 .BR mount (8).)
  57 Each suboption may include an associated value,
  58 which is separated from the suboption name by an equal sign.
  59 The following is an example of the kind of string
  60 that might be passed in
  61 .IR optionp :
  62 .sp
  63 .in +4n
  64 .B ro,name=xyz
  65 .in
  66
  67 The
  68 .I tokens
  69 argument is a pointer to a NULL-terminated list of the tokens that
  70 .BR getsubopt ()
  71 will look for in
  72 .IR optionp .
  73 The tokens should be distinct, null-terminated strings containing at
  74 least one character, with no embedded equal signs or commas.
  75
  76 Each call to
  77 .BR getsubopt ()
  78 returns information about the next unprocessed suboption in
  79 .IR optionp .
  80 The first equal sign in a suboption (if any) is interpreted as a
  81 separator between the name and the value of that suboption.
  82 The value extends to the next comma,
  83 or (for the last suboption) to the end of the string.
  84 If the name of the suboption matches a known name from
  85 .IR tokens ,
  86 and a value string was found,
  87 .BR getsubopt ()
  88 sets
  89 .I *valuep
  90 to the address of that string.
  91 The first comma in
  92 .I optionp
  93 is overwritten with a null byte, so
  94 .I *valuep
  95 is precisely the "value string" for that suboption.
  96
  97 If the suboption is recognized, but no value string was found,
  98 .I *valuep
  99 is set to NULL.
 100
 101 When
 102 .BR getsubopt ()
 103 returns,
 104 .I optionp
 105 points to the next suboption,
 106 or to the null byte ('\\0') at the end of the
 107 string if the last suboption was just processed.
 108 .SH RETURN VALUE
 109 If the first suboption in
 110 .I optionp
 111 is recognized,
 112 .BR getsubopt ()
 113 returns the index of the matching suboption element in
 114 .IR tokens .
 115 Otherwise, \-1 is returned and
 116 .I *valuep
 117 is the entire
 118 .IB name [= value ]
 119 string.
 120
 121 Since
 122 .I *optionp
 123 is changed, the first suboption before the call to
 124 .BR getsubopt ()
 125 is not (necessarily) the same as the first suboption after
 126 .BR getsubopt ().
 127 .SH CONFORMING TO
 128 POSIX.1-2001.
 129 .SH NOTES
 130
 131 Since
 132 .BR getsubopt ()
 133 overwrites any commas it finds in the string
 134 .IR *optionp ,
 135 that string must be writable; it cannot be a string constant.
 136 .SH EXAMPLE
 137 The following program expects suboptions following a "\-o" option.
 138
 139 .nf
 140 #define _XOPEN_SOURCE 500
 141 #include <stdlib.h>
 142 #include <assert.h>
 143 #include <stdio.h>
 144
 145 int main(int argc, char **argv)
 146 {
 147     enum {
 148         RO_OPT = 0,
 149         RW_OPT,
 150         NAME_OPT
 151     };
 152     char *const token[] = {
 153         [RO_OPT]   = "ro",
 154         [RW_OPT]   = "rw",
 155         [NAME_OPT] = "name",
 156         NULL
 157     };
 158     char *subopts;
 159     char *value;
 160     int opt;
 161
 162     int readonly = 0;
 163     int readwrite = 0;
 164     char *name = NULL;
 165     int errfnd = 0;
 166
 167     while ((opt = getopt(argc, argv, "o:")) != \-1) {
 168         switch (opt) {
 169         case \(aqo\(aq:
 170             subopts = optarg;
 171             while (*subopts != \(aq\\0\(aq && !errfnd) {
 172
 173             switch (getsubopt(&subopts, token, &value)) {
 174             case RO_OPT:
 175                 readonly = 1;
 176                 break;
 177
 178             case RW_OPT:
 179                 readwrite = 1;
 180                 break;
 181
 182             case NAME_OPT:
 183                 if (value == NULL) {
 184                     fprintf(stderr, "Missing value for "
 185                             "suboption \(aq%s\(aq\\n", token[NAME_OPT]);
 186                     errfnd = 1;
 187                     continue;
 188                 }
 189
 190                 name = value;
 191                 break;
 192
 193             default:
 194                 fprintf(stderr, "No match found "
 195                         "for token: /%s/\\n", value);
 196                 errfnd = 1;
 197                 break;
 198             }
 199         }
 200         if (readwrite && readonly) {
 201             fprintf(stderr, "Only one of \(aq%s\(aq and \(aq%s\(aq can be "
 202                     "specified\\n", token[RO_OPT], token[RW_OPT]);
 203             errfnd = 1;
 204         }
 205         break;
 206
 207         default:
 208             errfnd = 1;
 209         }
 210     }
 211
 212     if (errfnd || argc == 1) {
 213         fprintf(stderr, "\\nUsage: %s \-o <suboptstring>\\n", argv[0]);
 214         fprintf(stderr, "suboptions are \(aqro\(aq, \(aqrw\(aq, "
 215                 "and \(aqname=<value>\(aq\\n");
 216         exit(EXIT_FAILURE);
 217     }
 218
 219     /* Remainder of program... */
 220
 221     exit(EXIT_SUCCESS);
 222 }
 223 .fi
 224 .SH SEE ALSO
 225 .BR getopt (3)