GETARG(3)                  UNIX Programmer's Manual                  GETARG(3)


     getarg, arg_printusage - collect command line options


     getarg(struct getargs *args, size_t num_args, int argc, char **argv,
             int *optind)

     arg_printusage(struct getargs *args, size_t num_args,
             const char *progname, const char *extra_string)


     getarg() collects any command line options given to a program in an easi-
     ly used way.  arg_printusage() pretty-prints the available options, with
     a short help text.

     args is the option specification to use, and it's an array of struct
     getargs elements.  num_args is the size of args (in elements).  argc and
     argv are the argument count and argument vector to extract option from.
     optind is a pointer to an integer where the index to the last processed
     argument is stored, it must be initialised to the first index (minus one)
     to process (normally 0) before the first call.

     arg_printusage take the same args and num_args as getarg; progname is the
     name of the program (to be used in the help text), and extra_string is a
     string to print after the actual options to indicate more arguments. The
     usefulness of this function is realised only be people who has used pro-
     grams that has help strings that doesn't match what the code does.

     The getargs struct has the following elements.

     struct getargs{
         const char *long_name;
         char short_name;
         enum { arg_integer,
         } type;
         void *value;
         const char *help;
         const char *arg_help;

     long_name is the long name of the option, it can be NULL, if you don't
     want a long name.  short_name is the characted to use as short option, it
     can be zero. If the option has a value the value field gets filled in
     with that value interpreted as specified by the type field.  help is a
     longer help string for the option as a whole, if it's NULL the help text
     for the option is omitted (but it's still displayed in the synopsis).
     arg_help is a description of the argument, if NULL a default value will
     be used, depending on the type of the option:

     arg_integer        the argument is a signed integer, and value should
                        point to an int.

     arg_string         the argument is a string, and value should point to a


     arg_flag           the argument is a flag, and value should point to a
                        int. It gets filled in with either zero or one, de-
                        pending on how the option is given, the normal case
                        being one. Note that if the option isn't given, the
                        value isn't altered, so it should be initialised to
                        some useful default.

     arg_negative_flag this is the same as arg_flag but it reverses the mean-
                        ing of the flag (a given short option clears the
                        flag), and the synopsis of a long option is negated.

     arg_strings        the argument can be given multiple times, and the val-
                        ues are collected in an array; value should be a
                        pointer to a struct getarg_strings structure, which
                        holds a length and a string pointer.

     arg_double         argument is a double precision floating point value,
                        and value should point to a double.

     arg_collect        allows more fine-grained control of the option parsing
                        process.  value should be a pointer to a
                        getarg_collect_info structure:

                        typedef int (*getarg_collect_func)(int short_opt,
                                                           int argc,
                                                           char **argv,
                                                           int *optind,
                                                           int *optarg,
                                                           void *data);

                        typedef struct getarg_collect_info {
                            getarg_collect_func func;
                            void *data;
                        } getarg_collect_info;

                        With the func member set to a function to call, and
                        data to some application specific data. The parameters
                        to the collect function are:

                        short_flag non-zero if this call is via a short option
                        flag, zero otherwise

                        argc, argv the whole argument list

                        optind pointer to the index in argv where the flag is

                        optarg pointer to the index in argv[*optind] where the
                        flag name starts

                        data application specific data

                        You can modify *optind, and *optarg, but to do this
                        correct you (more or less) have to know about the in-
                        ner workings of getarg.

                        You can skip parts of arguments by increasing *optarg
                        (you could implement the -z3 set of flags from gzip
                        with this), or whole argument strings by increasing
                        *optind (let's say you want a flag -c x y z to specify
                        a coordinate); if you also have to set *optarg to a
                        sane value.

                        The collect function should return one of
                        ARG_ERR_NO_MATCH, ARG_ERR_BAD_ARG, ARG_ERR_NO_ARG on
                        error, zero otherwise.

                        For your convenience there is a function,
                        getarg_optarg(), that returns the traditional argument
                        string, and you pass it all arguments, sans data, that
                        where given to the collection function.

                        Don't use this more this unless you absolutely have

     Option parsing is similar to what getopt uses. Short options without ar-
     guments can be compressed (-xyz is the same as -x -y -z), and short op-
     tions with arguments take these as either the rest of the argv-string or
     as the next option (-ofoo, or -o foo).

     Long option names are prefixed with -- (double dash), and the value with
     a = (equal), --foo=bar. Long option flags can either be specified as they
     are (--help), or with an (boolean parsable) option (--help=yes,
     --help=true, or similar), or they can also be negated (--no-help is the
     same as --help=no), and if you're really confused you can do it multiple
     times (--no-no-help=false, or even --no-no-help=maybe).


     #include <stdio.h>
     #include <string.h>
     #include <getarg.h>

     char *source = "Ouagadougou";
     char *destination;
     int weight;
     int include_catalog = 1;
     int help_flag;

     struct getargs args[] = {
         { "source",      's', arg_string,  &source,
           "source of shippment", "city" },
         { "destination", 'd', arg_string,  &destination,
           "destination of shippment", "city" },
         { "weight",      'w', arg_integer, &weight,
           "weight of shippment", "tons" },
         { "catalog",     'c', arg_negative_flag, &include_catalog,
           "include product catalog" },
         { "help",        'h', arg_flag, &help_flag }

     int num_args = sizeof(args) / sizeof(args[0]); /* number of elements in args */

     const char *progname = "ship++";

     main(int argc, char **argv)
         int optind = 0;
         if (getarg(args, num_args, argc, argv, &optind)) {
             arg_printusage(args, num_args, progname, "stuff...");
             exit (1);
         if (help_flag) {
             arg_printusage(args, num_args, progname, "stuff...");
             exit (0);
         if (destination == NULL) {
             fprintf(stderr, "%s: must specify destination\n", progname);
         if (strcmp(source, destination) == 0) {
             fprintf(stderr, "%s: destination must be different from source\n");
         /* include more stuff here ... */

     The output help output from this program looks like this:

     $ ship++ --help
     Usage: ship++ [--source=city] [-s city] [--destination=city] [-d city]
        [--weight=tons] [-w tons] [--no-catalog] [-c] [--help] [-h] stuff...
     -s city, --source=city      source of shippment
     -d city, --destination=city destination of shippment
     -w tons, --weight=tons      weight of shippment
     -c, --no-catalog            include product catalog


     It should be more flexible, so it would be possible to use other more
     complicated option syntaxes, such as what ps(1),  and tar(1),  uses, or
     the AFS model where you can skip the flag names as long as the options
     come in the correct order.

     Options with multiple arguments should be handled better.

     Should be integreated with SL.

     It's very confusing that the struct you pass in is called getargS.



 ROKEN                        September 24, 1999                             4

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