# FBB::Arg(3bobcat)

## Command Line Arguments
(libbobcat-dev_5.07.03)

## 2005-2021

## NAME

FBB::Arg - A singleton class interfacing command line arguments

## SYNOPSIS

#include <bobcat/arg>
Linking option: -lbobcat

## DESCRIPTION

Singleton class (see Gamma et al., 1995) built around getopt()(3) and getopt_long()(3). The class handles short- and long command-line options,

## NAMESPACE

FBB
All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace FBB.

## INHERITS FROM

-

## ENUMERATION

The FBB::Arg::Type enumeration is defined by the FBB::Arg class. It is used to specify whether or not long options require arguments. It defines the following values: None, Required, Optional.

- None: the long option does not use an argument;
- Required: the long option requires an argument value;
- Optional: the long option may optionally be provided with an argument value;

These values are used when constructing objects of the following (nested) class FBB::Arg::LongOption.

## THE NESTED CLASS FBB::Arg::LongOption

Long options are defined using objects of the nested class FBB::Arg::LongOption. This class provides the following constructors:

- FBB::Arg::LongOption(char const *name, FBB::Arg::Type type = FBB::Arg::None):
  This constructor is used to define a long option for which no corresponding short option is defined. The parameter name is the name of the long option (without prefixing the -- characters, which are required when specifying the long option).

- FBB::Arg::LongOption(char const *name, int optionChar):
  This constructor is used to define a long option for which a corresponding short option is defined. The parameter name is the name of the long option (without prefixing the -- characters, which are required when specifying the long option).

In a program, long options may be specified as follows:

- First, construct an array

          FBB::Arg::LongOption longOptions[] = { c1, c2, ... cn };

  Where c1, c2, ..., cn are n constructor invocations of FBB::Arg::LongOption() constructors

- Next, pass longOptions, LongOptions + n as 2nd and 3rd arguments to Arg's member initialize()

The class LongOptions is primarily used internally by the Arg object, but it can also be used outside of the Arg object. For that situation the following members are provided:

- std::string const &longName() const:
  returns the LongOption's long option name;
- int optionChar() const:
  returns the LongOption's option character (or one of the Arg::Type enumeration values if there is no option character associated with the LongOption).

## CONSTRUCTORS

Since the class is a Singleton there are no public constructors. Instead, static members are offered for initializing and accessing the single FBB::Arg object.

## STATIC MEMBERS

- FBB::Arg &initialize(char const *optstring, int argc, char **argv):
  Initializes the FBB::Arg singleton. May be called only once. Throws an FBB::Exception exception if called repeatedly or if called with argv containing an undefined option. If so, the Exception object's what() member provides details. A reference to the singleton object is returned.

- FBB::Arg &initialize(char const *optstring, LongOption const *const begin, LongOption const *const end, int argc, char **argv):
  Initializes the FBB::Arg singleton. Accepts two iterators of an array of Arg::LongOption objects. May be called only once. Throws an FBB::Exception exception if called repeatedly or if called with argv containing a undefined option. If so, the Exception object's what() member provides details. See the description of Arg::LongOption below. A reference to the singleton object is returned.

  The parameter optstring must point to a null-terminated byte string (NTBS) containing option characters, possibly postfixed by:

  - a colon (:), indicating that the option requires an option value.
  - a double colon (::), indicating that the option has an optional argument. With short options the option value is considered absent unless it it directly attached to the short option (e.g., -tvalue). Long options optionally accepting arguments should always immediately be followed by an assignment character (=). Here the option's value must immediately follow the = character, and must start with a non-blank character. E.g., --value= indicates an absent option value, --value=text indicates the option's value equals text. If an option value itself contains blanks, it must be surrounded by single or double quotes (e.g., -t'this value', or --text='this value'). The surrounding quotes are not part of the option's value.

- FBB::Arg &instance():
  Returns a reference to the iitialized Arg object. If called before initialization, an FBB::Exception exception is thrown.

## OVERLOADED OPERATOR

- char const *operator[](size_t idx) const:
  Returns argument[idx], after having removed all specified options. It returns 0 if no arg[x] is available. The program's name (argv[0]) is NOT counted here: index 0 refers to the first ARGUMENT, e.g., the program's argv[1].

## NON-STATIC MEMBER FUNCTIONS

- char const **argPointers() const:
  Returns argv-like set of pointers to all remaining arguments. The last element is guaranteed to be a 0-pointer. The first nArg() elements point to the respective values of the NTBS arguments that were passed to the program.

  The caller is responsible for returning the array of pointers to the common pool, but should not delete the C-strings to which the pointers point. The following two statements illustrate this:

          char const **ptr = Arg::instance().argPointers();
          delete[] ptr;

- std::string const &basename() const:
  Returns the program's basename.

- size_t beyondDashes() const:
  Returns the index of the first argument after a -- argument or returns nArgs() if no -- argument was encountered.
  A -- argument ends Arg's argument processing, and all arguments beyond the first -- argument are kept `as is'. The beyondDashes member returns the index of the first argument beyond the -- argument, which itself is removed from the remaining set of arguments.

- void help() const:
  If the member versionHelp (see below) has been called then this member calls the usage function that was passed to versionHelp. If versionHelp has not been called (i.e., if no usage function has been specified) an FBB::Exception is thrown.

- size_t nArgs() const:
  Returns the number of arguments left after option-removal. The program name argv[0] is NOT counted here.

- size_t nLongOptions() const:
  Returns the number of long options not having short option synonyms If long options are multiply specified, then each specification is counted.

- size_t nOptions() const:
  Returns the number of specified single character options. If short options have long option synonyms, then these long option synonyms are counted as if they were specified as single character options. If single character options (or their long option synonyms) are multiply specified, then each specification is separately counted.

- size_t option(int option) const:
  Returns the number of times `option' was specified (or its long option synonym, if defined).

- size_t option(std::string const &options) const:
  Returns the number of times each of the options specified in the `option' argument were specified (or their long option synonyms). Note that each character in options must specify a single-character option.

- size_t option(string *value, int option) const:
  Returns the number of times the provided option (or its long option synonym) was present. If the return value is non-zero then the value of the first occurrence of this option is stored in *value, which is left untouched if `option' was not present. The parameter value may be initialized to 0 if the option does not have a value or if the option's value should not be stored.

- size_t option(size_t idx, string *value, int option) const:
  Returns the number of times the provided option (or its long option synonym) was present. If the return value is non-zero then the value of the idxth occurrence (0-based offset) of this option is stored in *value, which is left untouched if `option' was not present or if idx is or exceeds the number of specifications of the provided option. 0 may be specified for value if the option does not have a value or if the value should not be stored.

- size_t option(size_t *idx, string *value, int option) const:
  Returns the number of times the provided option (or its long option synonym) was present. If the return value is non-zero then the offset (within the series of option specifications) of the first option having a non-empty option value is returned in *idx, while its option value is stored in *value. Both *value and *idx are left untouched if `option' was not present. 0 may be specified for value if the option does not have a value or if the value should not be stored.

- size_t option(string *value, char const *longOption) const:
  Returns the number of times the specified long option (not having a single-character synonym) was present. Its value is then stored in *value, which is left untouched if the long option was not present. 0 may be specified for value if the option does not have a value or if the value should not be stored.

- size_t option(size_t idx, string *value, char const * longOption) const:
  Returns the number of times the provided long option (not having a single-character synonym) was present. If the return value is non-zero then the value of the idxth occurrence (0-based offset) of this long option is stored in *value, which is left untouched if the long option was not present or if idx is or exceeds the number of specifications of the provided long option. 0 may be specified for value if the long option does not have a value or if the value should not be stored.

- size_t option(size_t *idx, string *value, int longOption) const:
  Returns the number of times the provided long option (not having a single-character synonym) was present. If the return value is non-zero then the offset (within the series of this long option specifications) of the first long option having a non-empty option value is returned in *idx, while its option value is stored in *value. Both *value and *idx are left untouched if long option was not present. 0 may be specified for value if the long option does not have a value or if the value should not be stored.

- void versionHelp(void (*usage)(std::string const &progname), char const *version, size_t minArgs, int helpFlag = 'h', int versionFlag = 'v') const:
  If the helpFlag was specified usage() is called with argument basename() whereafter the program throws int 0.

  If versionFlag was specified the program's name (using basename()) and version is displayed to std::cout whereafter the program throws int 0.

  If there are fewer arguments than minArgs usage() is called with argument basename() and the program ends with exit value 1.

  Note that versionhelp compares minArgs against nArgs. If minArgs should be compaired against the number of arguments up to a possible `--' argument (i.e., beyondDashes' return value), then add nArgs() - beyondDashes() to the minArg argument. E.g.,

          arg.versionHelp(usage, version, 2 + arg.nArgs()
                                            - arg.beyondDashes());

  The address of the usage() function, the current version and the minimum number of arguments must be specified. Default argument values are provided for the option flags.

## EXAMPLE

The following example illustrates defining long options and shows an initialization. It is not a full-fledched example in the sense of a small runnable program.

    #include <bobcat/arg>

    using namespace FBB;
    using namespace std;

    namespace   // the anonymous namespace can be used here
    {
        Arg::LongOption longOptions[] =
        {
            Arg::LongOption{"debug"},
            Arg::LongOption{"filenames", 'f'},
            Arg::LongOption{"help", 'h'},
            Arg::LongOption{"version", 'v'},
        };
        auto longEnd = longOptions + size(longOptions);
    }

    int main(int argc, char **argv)
    try
    {
        Arg &arg = Arg::initialize("df:hv",
                        longOptions, longEnd,
                        argc, argv);

        // code using arg, etc.
    }
    catch (exception const &err)     // handle exceptions
    {
        cerr << err.what() << '\n';
        return 1;
    }

## FILES

bobcat/arg - defines the class interface

## SEE ALSO

bobcat(7)

## BUGS

None Reported.

## BOBCAT PROJECT FILES

- https://fbb-git.gitlab.io/bobcat/: gitlab project page;
- bobcat_5.07.03-x.dsc: detached signature;
- bobcat_5.07.03-x.tar.gz: source archive;
- bobcat_5.07.03-x_i386.changes: change log;
- libbobcat1_5.07.03-x_*.deb: debian package containing the libraries;
- libbobcat1-dev_5.07.03-x_*.deb: debian package containing the libraries, headers and manual pages;

## BOBCAT

Bobcat is an acronym of `Brokken's Own Base Classes And Templates'.

## COPYRIGHT

This is free software, distributed under the terms of the GNU General Public License (GPL).

## AUTHOR

Frank B. Brokken (f.b.brokken@rug.nl).