man3/getsubopt.3

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  23 .TH GETSUBOPT 3 2007-05-05 "GNU" "Linux Programmer's Manual"
  24 .SH NAME
  25 getsubopt \- parse suboption arguments from a string
  26 .SH SYNOPSIS
  27 .B #define _XOPEN_SOURCE 500
  28 .br
  29 .B #include <stdlib.h>
  30
  31 .B int getsubopt(char
  32 .BI ** optionp ,
  33 .B char *const
  34 .BI * tokens ,
  35 .B char
  36 .IB valuep );
  37 .SH DESCRIPTION
  38 .BR getsubopt ()
  39 parses the list of comma-separated suboptions provided in
  40 .IR optionp .
  41 (Such a suboption list is typically produced when
  42 .BR getopt (3)
  43 is used to parse a command line;
  44 see for example the \fI-o\fP option of
  45 .BR mount (8).)
  46 Each suboption may include an associated value,
  47 which is separated from the suboption name by an equal sign.
  48 The following is an example of the kind of string
  49 that might be passed in
  50 .IR optionp :
  51 .sp
  52 .RS
  53 .B ro,name=xyz
  54 .RE
  55
  56 The
  57 .I tokens
  58 argument is a pointer to a NULL-terminated list of the tokens that
  59 .BR getsubopt ()
  60 will look for in
  61 .IR optionp .
  62 The tokens should be distinct, null-terminated strings containing at
  63 least one character, with no embedded equal signs or commas.
  64
  65 Each call to
  66 .BR getsubopt ()
  67 returns information about the next unprocessed suboption in
  68 .IR optionp .
  69 The first equal sign in a suboption (if any) is interpreted as a
  70 separator between the name and the value of that suboption.
  71 The value extends to the next comma,
  72 or (for the last suboption) to the end of the string.
  73 If the name of the suboption matches a known name from
  74 .IR tokens ,
  75 and a value string was found,
  76 .BR getsubopt ()
  77 sets
  78 .RI * valuep
  79 to the address of that string.
  80 The first comma in
  81 .I optionp
  82 is overwritten with a null byte, so
  83 .RI * valuep
  84 is precisely the "value string" for that suboption.
  85
  86 If the suboption is recognized, but no value string was found,
  87 .RI * valuep
  88 is set to NULL.
  89
  90 When
  91 .BR getsubopt ()
  92 returns,
  93 .I optionp
  94 points to the next suboption, or to the null character at the end of the
  95 string if the last suboption was just processed.
  96 .SH RETURN VALUE
  97 If the first suboption in
  98 .I optionp
  99 is recognized,
 100 .BR getsubopt ()
 101 returns the index of the matching suboption element in
 102 .I tokens .
 103 Otherwise, \-1 is returned and
 104 .RI * valuep
 105 is the entire
 106 .IB name [= value ]
 107 string.
 108
 109 Since
 110 .RI * optionp
 111 is changed, the first suboption before the call to
 112 .BR getsubopt ()
 113 is not (necessarily) the same as the first suboption after
 114 .BR getsubopt ().
 115 .SH CONFORMING TO
 116 POSIX.1-2001.
 117 .SH NOTES
 118
 119 Since
 120 .BR getsubopt ()
 121 overwrites any commas it finds in the string
 122 .RI * optionp ,
 123 that string must be writable; it cannot be a string constant.
 124 .SH EXAMPLE
 125 The following program excepts suboptions following a "\-o" option.
 126
 127 .nf
 128 #define _XOPEN_SOURCE 500
 129 #include <stdlib.h>
 130 #include <assert.h>
 131 #include <stdio.h>
 132
 133 int main(int argc, char **argv)
 134 {
 135     enum {
 136         RO_OPT = 0,
 137         RW_OPT,
 138         NAME_OPT
 139     };
 140     char *const token[] = {
 141         [RO_OPT]   = "ro",
 142         [RW_OPT]   = "rw",
 143         [NAME_OPT] = "name",
 144         NULL
 145     };
 146     char *subopts;
 147     char *value;
 148     int opt;
 149
 150     int readonly = 0;
 151     int readwrite = 0;
 152     char *name = NULL;
 153     int errfnd = 0;
 154
 155     while ((opt = getopt(argc, argv, "o:")) != \-1) {
 156         switch (opt) {
 157         case 'o':
 158             subopts = optarg;
 159             while (*subopts != '\\0' && !errfnd) {
 160
 161             switch (getsubopt(&subopts, token, &value)) {
 162                 case RO_OPT:
 163                     readonly = 1;
 164                     break;
 165
 166                 case RW_OPT:
 167                     readwrite = 1;
 168                     break;
 169
 170                 case NAME_OPT:
 171                     if (value == NULL) {
 172                         fprintf(stderr, "Missing value for "
 173                                 "suboption '%s'\\n", token[NAME_OPT]);
 174                         errfnd = 1;
 175                         continue;
 176                     }
 177
 178                     name = value;
 179                     break;
 180
 181                 default:
 182                     fprintf(stderr, "No match found "
 183                             "for token: /%s/\\n", value);
 184                     errfnd = 1;
 185                     break;
 186                 }
 187             }
 188             if (readwrite && readonly) {
 189                 fprintf(stderr, "Only one of '%s' and '%s' can be "
 190                         "specified\\n", token[RO_OPT], token[RW_OPT]);
 191                 errfnd = 1;
 192             }
 193             break;
 194
 195         default:
 196             errfnd = 1;
 197         }
 198     }
 199
 200     if (errfnd || argc == 1) {
 201         fprintf(stderr, "\\nUsage: %s \-o <suboptstring>\\n", argv[0]);
 202         fprintf(stderr, "suboptions are 'ro', 'rw', "
 203                 "and 'name=<value>'\\n");
 204         exit(EXIT_FAILURE);
 205     }
 206
 207     /* Remainder of program... */
 208
 209     exit(EXIT_SUCCESS);
 210 }
 211 .fi
 212 .SH SEE ALSO
 213 .BR getopt (3),
 214 .BR feature_test_macros (7)