I often end up writing little command line programs that behave differently depending on the options that they are passed. Most of the software libraries that I publish include examples requiring command line options. I had been using the getopt() function to help me with the necessary parsing.

Since getopt() isn't ANSI, it's not included with all ANSI C compilers. That means that I need to include a copy of getopt() with any of my code samples so people with compilers that don't provide the getopt() function can still use my code. Fortunately there is at least one getopt() implementation published under version 2 of the GNU LGPL. The version even allows upgrading to new versions of the LGPL, so I had been using that in my projects licensed under version 2.1 of the LGPL.

When version 3 of the LGPL was released I decided that I wanted to explicitly license my projects under the newer version. There's no reason that I couldn't continue to use the version 2 getopt() library, but there are things that I don't like about getopt() that I wanted to change, and the license upgrade seemed like a good reason to write a library that worked the way I wanted it to work.

Now that my replacement library works pretty much the way that I want it to work, I am publishing it under version 3 of the GNU LGPL in hopes that they will be of use to other people.

The rest of this page discusses, the optlist library, my replacement for getopt().

Michael Dipperstein

Optlist Library


The optlist library provides the functions GetOptList() and FreeOptList(). The GetOptList() function is similar to getopt(). Its most notable differences are that it returns a linked list to the command line arguments and their parameters. One call to GetOptList() will return all of the command line options and their arguments.

Other Differences:

  • GetOptList() will not modify argc or argv
  • GetOptList() does not use global variables
  • GetOptList() is thread safe and reenterant
  • Unfortunately, GetOptList() allocates memory which must be freed one element at a time or by calling FreeOptList()

New Types and Prototypes

typedef struct option_t

char option;
char *argument;
int argIndex;
struct option_t *next;

} option_t;

option_t *GetOptList(int argc, char *const argv[], char *const options);
void FreeOptList(option_t *list);


GetOptList()'s parameters "argc" and "argv" are usually the argument count and array as passed to the main() function on program invocation. An element of argv that starts with "-" is an option element. The character following the "-" is an option character.

The "options" parameter is a string containing legitimate option characters. If such a character is followed by a colon, the option requires an argument. (e.g. "a:bc?" a, b ,c, and, ? are all options. a should be followed by an argument.)

GetOptList() returns a linked list of type option_t. The *next field of the element at the end of the list will be set to NULL. The option field will contain the option character. If the option accepts an argument, a pointer to the text that follows in the same argv-element, or the text of the following argv-element will be stored in the arguement field. Otherwise the arguement field is set to NULL. The index of the argv-element containing the argument will be stored in the argIndex. If there is no argument, the field will contain OL_NOINDEX.

FreeOptList() accepts one parameter, *list, a pointer to the head of the option_t type list to be freed. FreeOptList() will free each element in the list and set the value of list to NULL.


option_t *optList, *thisOpt;

/* get list of command line options and their arguments */
optList = NULL;
optList = GetOptList(argc, argv, "a:bcd:ef?");

/* display results of parsing */
while (optList != NULL)

thisOpt = optList;
optList = optList->next;

if ('?' == thisOpt->option)
printf("Usage: %s <options>\n\n", RemovePath(argv[0]));
printf(" -a : option excepting argument.\n");
printf(" -b : option without arguments.\n");
printf(" -c : option without arguments.\n");
printf(" -d : option excepting argument.\n");
printf(" -e : option without arguments.\n");
printf(" -f : option without arguments.\n");
printf(" -? : print out command line options.\n\n");

FreeOptList(thisOpt); /* done with this list, free it */

printf("found option %c\n", thisOpt->option);

if (thisOpt->argument != NULL)
printf("\tfound argument %s", thisOpt->argument);
printf(" at index %d\n", thisOpt->argIndex);
printf("\tno argument for this option\n");

free(thisOpt); /* done with this item, free it */



All the source code that I have provided is written in strict ANSI C. I would expect it to build correctly on any machine with an ANSI C compiler. I have tested the code compiled with gcc on Linux and mingw on Windows XP.

Actual Software

I am releasing my implementation of the OptList() library under the LGPL. As I add enhancements or fix bugs, I will post them here as newer versions. The larger the version number, the newer the version. I will retaining the older versions for historical reasons. I recommend that most people download the newest version unless there is a compelling reason to do otherwise.

Each version is contained in its own zipped archive which includes the source files and brief instructions for building an executable. None of the archives contain executable programs. A copy of the archives may be obtained by clicking on the links below.

Version Comment
Version 0.4 Adds the FindFileName() function to find where the file name starts in a path, because I always use it with GetOptList().
  Written with tighter adherence to Michael Barr's Top 10 Bug-Killing Coding Standard Rules.
Version 0.3 Adds support for multiple options after a single dash (−).
Version 0.2 Adds FreeOptList() function.
Version 0.1 Initial Release.

If you have any further questions or comments, you may contact me by e-mail. My e-mail address is: mdipper@alumni.engr.ucsb.edu

Last updated on November 23, 2014