Arg_parser is an argument parser that follows POSIX and GNU conventions for command line arguments. There exist C++ and C versions of Arg_parser. The C++ version is implemented as a C++ class, while the C version is implemented as a single struct plus associated functions. Both are simpler, easier to use, and safer than 'getopt_long'.

For maximum stability, Arg_parser is self-contained. It extracts all the information it needs from its arguments to avoid refering to them later. This avoids index-out-of-bounds errors.

Arg_parser does not modify its arguments, nor uses any global variables. So you may create more than one parser in your program if you need or want to.

The C++ version of Arg_parser can also parse options from configuration files.

To use Arg_parser in your own programs simply copy the files 'arg_parser.h' and '' (or 'carg_parser.h' and 'carg_parser.c' for the C version) in your source tree. See the file '' ('cmain.c') for an example of use.

Arg_parser was developed as the argument parser for GNU moe, because moe's argument parsing is rather complex. Then I used it in my other projects, including GNU ddrescue, GNU ed, lzip, GNU ocrad, tarlz, and zutils, with excellent results.


The manual is available in the info system of the GNU Operating System. Use info to access the top level info page. Use info arg_parser to access the Arg_parser section directly.

An online manual for Arg_parser can be found at manual/arg_parser_manual.html.


The latest released version of Arg_parser can be found at You may also subscribe to arg-parser-bug and receive an email every time a new version is released.

To decompress Arg_parser tarballs you may need lzip from Then use "tar -xf arg_parser[version].tar.lz" or "lzip -cd arg_parser[version].tar.lz | tar -xf -" to extract the files.

How to Get Help

For general discussion of errors (bugs) in Arg_parser, the mailing list is the most appropriate forum. Please send messages as plain text. Please do not send messages encoded as HTML nor encoded as base64 nor included as multiple formats. Please include a descriptive subject line with the word "arg_parser" in it.

An archive of the bug report mailing list is available at

How to Help

To contact the author, either to report an error (bug) or to contribute fixes or improvements, send mail to Please send messages as plain text. If posting patches they should be in unified diff format against the latest version. They should include a text description.

See also the Arg_parser project page at Savannah.


This library is free software distributed under a 2-clause BSD license.

Valid HTML 4.01 Strict

Copyright © 2022 Antonio Diaz Diaz

You are free to copy, modify, and distribute all or part of this article without limitation.

Updated: 2022-02-05

This page does not use javascript.