# FBB::Arg(3bobcat)

## Command Line Arguments
(libbobcat-dev_6.06.02)

## 2005-2024

## 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_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 defining long options (like --version), which are defined as objects of the (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 specifying the -- characters which are only required when specifying a long option when calling a program).

- 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 specifying the -- characters which are only required when specifying a long option when calling a program).

To define long options use the following procedure:

- 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 arguments to an Arg::initialize member that supports long options.

Objects of the class LongOptions are normally used internally by the Arg object, but they can also be used outside of the Arg object. For that situation the following members are available:

- 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 Arg is a singleton there are no public constructors. Instead, static members are available to initialize and to access the single FBB::Arg object.

## STATIC MEMBERS

All initialize members initialize the FBB::Arg singleton, and can only be called once. An exception is thrown when called multiple times. All initialize members return a reference to the initialized Arg singleton object.

All initialize members define the parameters argc and argv which are interpreted as main's argc and argv parameters. When an argv element points to two consecutive dashes (--) then that element is ignored, and all of argv's subsequent elements are considered arguments instead of options.

- FBB::Arg &Arg::initialize(char const *optstring, int argc, char **argv):
  The parameter optstring is a null-terminated byte string (NTBS) optionally starting with a + character, but otherwise containing option characters. One or two colons may be postfixed to option characters:

  > - a single colon (:) indicates that the option requires an option value.
  > - a double colon (::) indicates that the option has an optional argument. With short options the option value is considered absent unless it is attached to the short option (e.g., -tvalue). Long options optionally accepting arguments should always immediately be followed by an assignment character (=), immediately followed by the option's value (which 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.

  When optstring's first character is + then all non-specified options are considered arguments, appearing in the final arguments list at their current argument positions. E.g., when optstring is +ab and no long options are defined, then calling

          prog -a -z -b -yvalue --long arg1 arg2

  results in the member argv returning a vector containing the elements -z, -yvalue, --long, arg1, and arg2. If optstring's first character isn't + and an undefined option is encountered then an exception is thrown.

- FBB::Arg &Arg::initialize(int accept, char const *optstring, int argc, char **argv):
  Acts like the previous member, but in addition defines the parameter accept specifying an option character from where all subsequent arguments and options are considered arguments. To ignore accept the value 0 (not the character '0') can be specified or an initialize members can be used that does not define an accept parameter.

  When arguments contain both an accept option and two consecutive dashes then the first one is interpreted, resulting in all remaining argv elements being interpreted as mere arguments. For example, when specifying initialize('t', ...) and calling

          prog one -ttwo -c -- three

  then the member argv returns a vector containing the elements one, -tttwo, -c, --, and three (see also the member beyondDashes below).

- FBB::Arg &Arg::initialize(char const *optstring, Arg::LongOption const *const begin, Arg::LongOption const *const end, int argc, char **argv):

  Acts like the first Arg::initialize member, but in addition defines two parameters specifying the range of elements of an array of Arg::LongOption objects specifying long options. The parameter begin points to the first element of the range, the parameter end points just beyond the last element of the range. E.g., after defining

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

  the arguments passed to begin and end could be specified as

          initialize(..., longOptions, longOptions + size(longOptions), ...);

- FBB::Arg &Arg::initialize(char accept, char const *optstring, LongOption const *const begin, LongOption const *const end, int argc, char **argv):

  Acts like the previous Arg::initialize member, but in addition defines an accept parameter as defined by the second Arg::initialize member.

- FBB::Arg &Arg::instance():
  Once an Arg::initialize member has been called this member can be called from anywhere in the program (and it can be called multiple times), returning a reference to the initialized Arg object.

  If it is called before an Arg::initialize member has been called an exception is thrown.

## OVERLOADED OPERATOR

- char const *operator[](size_t idx) const:
  Returns argument[idx], after all options have been removed. 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

- string const &argv0() const:
  Returns the program's name as specified by argv[0] (see also the member basename);

- char const **argPointers() const:
  Returns argv-like set of pointers to all remaining arguments. Element nArgs() + 1 is a 0-pointer. The first nArgs() elements point to the respective values of the NTBS arguments that were passed to the program, after having removed the options.

  The caller is responsible for returning the array of pointers returned by this member to the common pool, but the caller should not delete the NTBSs to which the pointers point as illustrated by the following two statements:

          char const **ptr = Arg::instance().argPointers();
          delete[] ptr;   // don't delete ptr[idx] elements!

- std::vector<std::string> const &args() const:
  Returns a vector of strings containing all arguments after having removed all options. The program's name (argv[0]) is NOT included here: its first element refers to the first ARGUMENT, e.g., the program's argv[1];

- std::string const &basename() const:
  Returns the program's basename (i.e., argv0()'s value beyond the last directory separator);

- std::vector<std::string>::const_iterator begin() const:
  Returns the iterator to the program's first argument (i.e., args().begin()). This member, in combination with the member end, allows processing of all arguments by generic algorithms;

- size_t beyondDashes() const:
  Returns the index of the first argument beyond the -- argument or returns the index of the accept argument (whichever comes first) or returns nArgs() if no -- or accept argument was encountered. See also the member nArgs below;

- std::vector<std::string>::const_iterator end() const:
  Returns the iterator pointing beyond the program's last argument (i.e., args().end()). This member, in combination with the member begin, allows processing of all arguments by generic algorithms;

- void help() const:
  If the member versionHelp (see below) was 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 exception is thrown;

- size_t nArgs() const:
  Returns the number of arguments after having removed the options (i.e., it returns args().size()). Note that the program's name is not counted here;

- size_t nLongOptions() const:
  Returns the number of long options not having short option synonyms. Multiply specified long options are each 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_6.06.02-x.dsc: detached signature;
- bobcat_6.06.02-x.tar.gz: source archive;
- bobcat_6.06.02-x_i386.changes: change log;
- libbobcat1_6.06.02-x_*.deb: debian package containing the libraries;
- libbobcat1-dev_6.06.02-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).