ioccc/next/guidelines.md

# 29th International Obfuscated C Code Contest Official Guidelines

<p class="leftbar">
Copyright &copy; 2025 Leonid A. Broukhis and Landon Curt Noll.
</p>

All Rights Reserved.  Permission for personal, education or non-profit
use is granted provided this copyright and notice are included in its
entirety and remains unaltered.  All other uses must receive prior
permission in writing by [contacting the Judges](../contact.html).


# Guidelines Version

<p class="leftbar">
These Guidelines are version **29.08 2025-12-02**.
</p>

<p class="leftbar">
The <span style='font-size:28px;'><b>&verbar;</b></span> symbol
indicates an **change** from the previous IOCCC.
</p>

<p class="leftbar">
Because the **IOCCC29**  was a substantial rewrite, only **important
changes** from **IOCCC28** have been marked.
</p>

<div id="guidelines">
# Guidelines
</div>

These [Guidelines](guidelines.html) are **hints** and **suggestions**,
**NOT** [Rules](rules.html).

While submissions that violate the [Guidelines](guidelines.html) are
allowed, submissions that remain within the
[Guidelines](guidelines.html) are preferred.

You are encouraged to review the following [FAQs](../faq.html):

* [How to enter the IOCCC](../quick-start.html#enter)

* [Obtaining and compiling the most recent mkiocccentry
toolkit](../faq.html#mkiocccentry)

* [How to upload your submission](./submit.html)

While the contest is **[open](../faq.html#open)**, you may modify your
previously uploaded submission by rebuilding your submission with the
[mkiocccentry toolkit](https://github.com/ioccc-src/mkiocccentry), and
then re-uploading it to **the same slot number** on the [submit
server](https://submit.ioccc.org).

Be sure to read the [Rules](rules.html).


<div id="guideline1">
<div id="guideline1-c">
# Guidelines for [Rule 1 - C program](rules.html#rule1-c)
</div>
</div>

<p class="leftbar">
While you submission **MUST** be a C program, there is nothing wrong if
your `prog.c` file happens to also be a code for another language, say
an interpreter of JavaScript.
</p>

<p class="leftbar">
We would prefer if you do not use `#include` statements just to include
lots of data to circumvent [Rule 2 - Size
restrictions](rules.html#rule2-size) in an excessive way. This is what
they invented `fopen(3)` for. :-)
</p>

<p class="leftbar">
We would prefer if you do not require lots and lots of implicit defines
on the C compiler command line (i.e., lots of `-Dfoo`, and
`-Dcurds=whey` style command line args to the C compiler in the
Makefile) to get around the [Rule 2 - Size
restrictions](rules.html#rule2-size) in an excessive way.
</p>

<p class="leftbar">
Some use of `#include` statements (i.e. `-include stdio.h`) and/or
implicit `#define`s (i.e.  `-Dfoo=bar`) on the C compiler command line
is perfectly reasonable..
</p>

<p class="leftbar">
As a guide, consider the level of `#include` statements and/or implicit
defines on the C compiler command line that are found in [winning
Entries](https://www.ioccc.org/years.html), and try to **NOT** set a
new record.
</p>

<p class="leftbar">
If you believe you need to significantly abuse `#include` statements
and/or implicit defines on the C compiler command line, then try to
make a case for why in your submission's `remarks.md` file: maybe the
Judges won't reject your submission.
</p>


Jump to: [top](#)


<div id="guideline2">
<div id="guideline2-size">
# Guidelines for [Rule 2 - Size restrictions](rules.html#rule2-size)
</div>
</div>

<p class="leftbar">
You should pay attention to our observations on [code size and Rule 2
remarks for IOCCC28](../2024/index.html#code-size-and-rule-2).
</p>

Your submission must satisfy **BOTH** the
[Rule 2a - Gross Size](rules.html#rule2a-gross-size)
**AND**
[Rule 2b - Net Size](rules.html#rule2b-net-size) rules.

To check your code against
[Rule 2 - Size restrictions](rules.html#rule2-size), use the
`iocccentry(1)` tool. For example:

``` <!---sh-->
    iocccsize prog.c
```

The `iocccsize(1)` algorithm can be summarized as follows:

> The size tool counts most C reserved words (keyword, secondary, and
selected preprocessor keywords) as 1.  The size tool counts all other
bytes as 1 excluding ASCII whitespace, and excluding any '`;`', '`{`'
or '`}`' followed by ASCII whitespace, and excluding any '`;`', '`{`'
or '`}`' byte immediately before the end of file.
>
> ASCII whitespace includes ASCII tab, ASCII space, ASCII newline,
ASCII formfeed, and ASCII carriage return.
>
> When '`;`', '`{`' or '`}`' are within a C string, they may still not
be counted by the IOCCC size tool.

In cases where the above summary and the algorithm implemented by
`iocccsize(1)` conflict, the algorithm implemented by the minimum
required version of `iocccsize(1)` is preferred by the
[Judges](../judges.html).

Make sure `iocccsize` does not flag any issues with your `prog.c`.

**NOTE**: by default `iocccsize` will only report the size, unless the
code surpasses the limit.

There a much less need to `#define` C reserved words in an effort to
get around the size limits of [Rule 2 - Size
restrictions](rules.html#rule2-size) because of the `iocccsize(1)`
algorithm.

Yes Virginia, **the previous guideline sentence is an important hint**!

Don't expect the [Rule 2 - Size restrictions](rules.html#rule2-size) to
[change any time soon](../faq.html#size_slow_change).

See the FAQ on "[How has the Rule 2 size restrictions rule changed over
the years?](../faq.html#size_rule_history)".


Jump to: [top](#)


<div id="guideline3">
<div id="guideline3-register">
# Guidelines for [Rule 3 - Register for the IOCCC](rules.html#rule3-register)
</div>
</div>

<p class="leftbar">
If a group of people work on a submission, then they should [register
for the IOCCC](../quick-start.html#enter) using either a valid group
email address, or an email address for one of the authors.
</p>

<p class="leftbar">
Processing your registration is an activity overseen by a Judge.
Please be **patient** while a Judge processes your registration.
</p>

It can take a few days to process your registration and for the server
to email your details, therefore make sure to allow yourself ample time
to register and submit your entries; **DO NOT WAIT UNTIL THE FINAL
DAYS** to register!  The Judges are **NOT** responsible for delayed or
lost email or for those who wait until the last minute to try to
register!

<p class="leftbar">
If after a few days you believe your registration hasn't been process,
then [contact the Judges](../contact.html).
</p>

<p class="leftbar">
After your UUID and temporary password are emailed to you, you have up
to fortnight (**14 days**) to login and change your temporary password.
If you fail to change your temporary password by that deadline, then
you'll need to [contact the Judges](../contact.html) by email to
request a reset.
</p>

See the
FAQ on "[How to register for the IOCCC](register.html)".

See the
FAQ on "[Entering the IOCCC: the bare minimum you need to
know](../quick-start.html#enter)".


Jump to: [top](#)


<div id="guideline7">
<div id="guideline7-original">
# Guidelines for [Rule 7 - Original Work](rules.html#rule7-original-work)
</div>
</div>

While it is **NOT** required, you are allowed to use tools or services
such as:

* Code generators
* Static and runtime code analysis tools
* Machine learning tools
* Natural language models
* Large language models (LLMs)
* Code copilot tools
* So called "_AI services_"
* Etc.

The IOCCC has a rich history of remarkable winning entries created by
authors who skillfully employed various techniques (often their own
tools) to develop their code.  If you do make use of such tools or
services, then we **ENCOURAGE you to describe how you used such tools**
in your `remarks.md` file.

<p class="leftbar">
In short: you created it, you own it, its an original work **OR** you have
explicit permission to the work that you document in your remarks.
</p>

See the
FAQ on "[May I use AI, LLM, Virtual coding assistants, or similar tools
to write my submission?](../faq.html#ai)".


Jump to: [top](#)


<div id="guideline8">
<div id="guideline8-submitting">
# Guidelines for [Rule 8 - Submitting requirements](rules.html#rule8-submitting-requirements)
</div>
</div>

Do **NOT** register more than one account just to try and get around
the limit on the number of submission slots, because if you do and we
discover that you did so your submissions will be rejected for
violating the rules.


Jump to: [top](#)


<div id="guideline9">
<div id="guideline9-no-interactive-compiling-allowed">
<div id="guideline9-no-interactive">
# Guidelines for [Rule 9 - No interactive compiling allowed](rules.html#rule9-no-interactive)
</div>
</div>
</div>

Don't forget that the building of your program should be done **WITHOUT
human intervention**.  So don't do things such as:

``` <!---makefile-->
    prog: prog.c
        #echo this next line requires data from standard input
        cat > prog.c
        ${CC} prog.c -o prog
```

However, you can do something cute such as making your program do
something dumb (or cute) when it is built 'automatically', and when it
is run with a human involved, do something more clever.  For example,
one could put in their `Makefile`:

``` <!---makefile-->
    prog: prog.c
        ${CC} prog.c -DNON_HUMAN_COMPILE -o prog
        @echo "See remarks section about alternate ways to compile"
```

and then include special notes in your `remarks.md` file for alternate
/ human intervention based building.


Jump to: [top](#)


<div id="guideline11">
<div id="guideline11-abuse">
# Guidelines for [Rule 11 - Legal rule abuse](rules.html#rule11-legal-rule-abuse)
</div>
</div>

We do realize that there are holes in the [Rules](rules.html), and
invite submitters to attempt to apply creative rule interpretation.  A
rule abuse though, even if not rewarded, may result in a subsequent
rule change for future contests.

We sometime award '**Best abuse of the rules**' or '**Worst abuse of
the rules**', or some variation, to a submission that creatively
attempts to exploit a holes in the [Rules](rules.html).

When we do need to plug a hole in the [Rules](rules.html) or
[Guidelines](guidelines.html), we will attempt to use a very small
plug, if not smaller.

Or, maybe not. :-)

Legal rule abuse may involve, but is not limited to, doing things that
are technically allowed by the [Rules](rules.html) and yet do not fit
the spirit of what we intended to be submitted.

Legal abuse of the [Rules](rules.html) is **NOT** an invitation to
violate the [Rules](rules.html) (especially [Rule 17 - Use
mkiocccentry](./rules.html#rule17-mkiocccentry)). A submission that
violates the [rules](rules.html) in the opinion of the
[Judges](../judges.html), **WILL** be disqualified.  **_RULE ABUSE
CARRIES A CERTAIN LEVEL OF RISK!_**

If you intend to abuse the [Rules](rules.html), indicate so in your
`remarks.md` file.  You **MUST** try to justify, plead, beg, why you
consider your rule abuse to be allowed under the [Rules](rules.html).
Humor or creativity help plead a case.

As there is no guarantee that you will succeed, you might consider
submitting an alternate version that conforms to the
[Rules](rules.html), if it might otherwise be interesting; one that
does not abuse the [Rules](rules.html) and one that does, making sure
to note in the one that does not abuse the rules that this is another
version, so that the Judges do not assume you uploaded it by mistake.

If you do bypass the `mkiocccentry(1)` warnings about
[Rule 2a - Gross Size](rules.html#rule2a-gross-size)
and/or about
[Rule 2b - Net Size](rules.html#rule2b-net-size)
**or any other
rule** and submit it anyway, you **MUST** try to justify why the
[Judges](../judges.html) should not reject your submission due to a rule
violation, and **you would be wise** to do this towards the top of your
`remarks.md` file so as not to be overlooked.

We are often asked why the contest [Rules](rules.html) and
[Guidelines](guidelines.html) seem strange or contain mistakes, flaws,
or grammatical errors.  One reason is that we sometimes make genuine
mistakes, but in many cases such problems, flaws or areas of confusion
are deliberate.

Changes to [Rules](rules.html) and [Guidelines](guidelines.html) in
response to rule abuses, are done in a minimal fashion.  Often we will
deliberately leave behind holes (or introduce new ones) so that future
rule abuse can continue.  A clever author should be able to read and
"drive a truck through the holes" in the [Rules](rules.html) and
[Guidelines](guidelines.html).

At the risk of stating the obvious, this contest is a parody of the
software development process.  The [Rules](rules.html) and
[Guidelines](guidelines.html) are only part of the overall contest.
Even so, one might think the contest [Rules](rules.html) and
[Guidelines](guidelines.html) process as a parody of the sometimes
tragic mismatch between what a customer (or marketing) wants and what
engineering delivers. Real programmers must face obfuscated and
sometimes conflicting, ballooning specifications, and requirements from
marketing, sales, product management and even from customers themselves
on an all too regular basis.  This is one of the reasons why the
[Rules](rules.html) and [Guidelines](guidelines.html) are written in
obfuscated form.


Jump to: [top](#)


<div id="guideline12">
<div id="guideline12-utf8">
# Guidelines for [Rule 12 - UTF-8](rules.html#rule12-utf8)
</div>
</div>

The IOCCC no longer discourages the use of multibyte UTF-8 characters
in `C` code.


<div id="guideline13">
<div id="guideline13-nocr">
# Guidelines for [Rule 13 - No carriage returns in prog.c](rules.html#rule13-nocr)
</div>
</div>

We **DISLIKE** C code with trailing control-M's (`\r` or `\015`) that
results in compilation failures.

Some non-UNIX/non-Linux tools such as MS Visual C and MS Visual C++
leave trailing control-M's on lines.  Users of such tools should strip
off such control-M's before submitting their submissions.  In some
cases tools have a "Save As" option that will prevent such trailing
control-M's being added.

<p class="leftbar">
If your `prog.c` is near the [Rule 2a Gross
Size](rules.html#rule2a-gross-size) and/or [Rule 2b Net
Size](rules.html#rule2b-net-size) limit, you are permitted to **NOT**
end source with a newline.  If you need to do this, please document
that in your `remarks.md` file.
</p>

<p class="leftbar">
If your compiler complains about about not ending in a newline, please
note this in your `remarks.md` file, and if possible add an appropriate
`-Wno-` to the `CSILENCE` variable in your Makefile.
</p>


Jump to: [top](#)


<div id="guideline15">
<div id="guideline15-gnu-makefile">
# Guidelines for [Rule 15 - GNU Makefile](rules.html#rule15-gnu-makefile)
</div>
</div>

Submissions will be judged in an environment that has no **IDE**.  Any
submission that fails to compile/build because it requires an **IDE**
will be rejected.

<p class="leftbar">
We will use the GNU `make(1)` tool, your `Makefile`, as well as tools
found in the [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
(UNIX-like) environments, and commonly found on systems that reasonably
conform to the [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
in the building and compiling of your submission.
</p>

<p class="leftbar">
Your `Makefile` **MUST** be compatible with GNU `make` and we suggest
you use [Makefile.example](Makefile.example) as a template, renamed as
`Makefile` of course.
</p>

See the
FAQ on "[What are the detailed recommendations for a submission
Makefile?](../faq.html#makefile_details)".


Jump to: [top](#)


<div id="guideline17">
<div id="guideline17-mkiocccentry">
# Guidelines for [Rule 17 - Use mkiocccentry](rules.html#rule17-mkiocccentry)
</div>
</div>

<p class="leftbar">
We **STRONGLY** recommend you **do** install the most recent release of
[mkiocccentry toolkit](https://github.com/ioccc-src/mkiocccentry)
because use of older versions of the mkiocccentry toolkit are **HIGHLY
LIKELY** to be **REJECTED**!
</p>

<p class="leftbar">
If you submit your own JSON files (**OTHER THAN** `.auth.json` and
`.info.json`!) then they do **NOT** have to be valid JSON.
</p>

<p class="leftbar">
However, if you do provide invalid JSON files, **PLEASE** document and
**clearly explain** this in your `remarks.md` file.
</p>

<p class="leftbar">
An _extra file_ is defined as a file that is not `prog.c`,
`prog.alt.c`, `try.sh`, `try.alt.sh`, `remarks.md`, `Makefile`,
`.auth.json` and `.info.json`: unless it's not in the top level
directory, in which case it **IS** an _extra file_.
</p>

<p class="leftbar">
The **non**-extra files are considered _free files_, and do not count
towards the [Rule 17 - Use
mkiocccentry](rules.html#rule17-mkiocccentry) limit of **31** _extra
files_.
</p>

<p class="leftbar">
If you use an optional filename for something other than their intended
use in order to get past the file limit, we will consider that an abuse
of rules.
</p>

<p class="leftbar">
The `mkiocccentry` generated tarball does **NOT** reveal who you are!
For this reason, the tarball **MUST** be a **v7 format** tarball.
</p>

<p class="leftbar">
You should NOT use a tarball as an _extra file_ for a test-suite unless
you have a very good reason for this: if you do include a tarball as an
_extra file_, then you **MUST** specify why in your `remarks.md` file.
</p>

<p class="leftbar">
If you **DO** include a tarball as an _extra file_, and the build
process or the program extracts said tarball(s), the make `clobber`
rule **MUST** remove the extracted files.
</p>

<p class="leftbar">
Instead of including a large test-suite that requires a lot of files as
part of your submission, if your submission doesn't require the
test-suite to be available to run, then in your `remarks.md` you could
include URL where such a test-suite may be downloaded from and how to
use the test-suite to test your submission, assuming it does not reveal
who you are, i.e. **DO NOT** use a GitHub URL which contains your
username, in case the judges know who you are. See [Rule 16 - Anonymous
judging](rules.html#rule16-anonymous-judging).
</p>

<p class="leftbar">
If you **DO** include a tarball then make sure it uses the v7 format.
This is because it will not reveal who you are.
</p>

<p class="leftbar">
See the FAQ on "[extra files](../faq.html#extra-files)" for details on
how to make a v7 tarball.
</p>

<p class="leftbar">
We recommend that all markdown files in your submission observe our
[IOCCC markdown guidelines](../markdown.html).
</p>

See the
FAQ on "[What should I do with the `try.sh` and `try.alt.sh`
scripts?](../faq.html#try_scripts)".

See the
FAQ on "[What is a `.auth.json` file?](../faq.html#auth_json)".

See the
FAQ on "[What is a `.info.json` file?](../faq.html#info_json)".

See the
FAQ on "[How can I validate my submission
directory?](../faq.html#chksubmit)".

See the
FAQ on "[What permissions may my files be and what if I need different
permissions?](../faq.html#file_perms)".

See the
FAQ on "[What are the detailed recommendations for a submission
Makefile?](../faq.html#makefile_details)".

See the
FAQ on "[What are the details behind Rule 17 - Use
mkiocccentry?](../faq.html#rule17)".


Jump to: [top](#)


<div id="general">
<div id="general-guidelines">
# General Guidelines
</div>
</div>


<div id="general-overall-guidelines">
<div id="overall-guidelines">
## Overall Guidelines
</div>
</div>

<p class="leftbar">
The **official locale** of the **IOCCC** is **C**.
</p>

You are **encouraged** to examine the [winners of previous
contests](../years.html).

Because the [Rules](rules.html) change from year to year, some [past
winning entries](../years.html) may be rejected this year.  What was
_was_ unique and novel one year _might be 'old' the next year_.

A submission is usually examined in a number of ways.  We typically
apply a number of tests to a submission:

* look at the original source
* C pre-process the source ignoring `#include` lines
* C pre-process the source ignoring `#define` _and_ `#include` lines
* run it through a C beautifier (such as `clang-format(1)`)
* examine the algorithm
* compile it (with flags to enable all warnings)
* execute it
* ...and various other things only we know about :-)

You should consider how your submission looks in each of the above
tests.  You should ask yourself if your submission remains obscure
after it has been '_cleaned up_' by the C pre-processor and a C
beautifier.

Your submission need not pass all of the above tests as in certain
cases, a test is not important.

Submissions that compete for the '**strangest/most creative source
layout**' need not do as well as others in terms of their algorithm.

Given two submissions, we are more inclined to pick the submission that
does something interesting when it's executed.

**IMPORTANT:** Be sure that **your submission works** as documented in
your `remarks.md` file.

We sometimes make an effort to debug a submission that has a slight
problem, particularly in or near the final round.  On the other hand,
we have seen some otherwise excellent submissions fall down because
they didn't work as documented.

If you submission has bugs and/or mis-features, you are **MUCH BETTER**
off documenting such bugs and/or mis-features in your `remarks.md`
file.

Consider an example of a [prime
number](https://en.wikipedia.org/wiki/Prime_number) printing program
that claims that 16 is a prime number.  Noting such a bug in your
`remarks.md` file could save your submission:

> "_this submission sometimes prints the 4th power of a prime by mistake_"

Sometimes a strange bug or (mis-)feature can even help the submission!
Of course, a correctly working submission might be better.

We tend to look down on a [prime
number](https://en.wikipedia.org/wiki/Prime_number) printer that claims
that 16 is a prime number.  Clever people will note that 16 might be
prime under certain conditions.  :-) Wise people, when submitting
something clever will **fully explain such cleverness** in their
submission's `remarks.md` file.

People who are considering to just use some complex mathematical
function or state machine to spell out something such as "_hello,
world!_" **really really, _and we do mean REALLY_, do need to be more
creative**.

Consider using misleading or subtle tricks layered on top of or under
an appropriate level of obfuscation.

A clean looking program with misleading comments and variable names
might be a **VERY GOOD START** to a great submission!

Try to avoid submissions that play music that some people believe is
copyrighted music.

Did we remember to indicate that programs that blatantly use some
complex state machine to do something simple, are boring?  We think we
did. :-)

Given two versions of the same program, one that is a compact blob of
code, and the other that is formatted more like a typical C program, we
tend to favor the second version.  Of course, a third version of the
same program that is formatted in an interesting and/or obfuscated way,
would definitely win over the first two!

Remember, you can submit more than one submission.  See the
[Rules](rules.html) for details (in particular, [Rule 8 - Submitting
requirements](rules.html#rule8-submitting-requirements)).

Please note that the C source below, besides lacking in obfuscation, is
**NOT** the smallest C source file that when compiled and run, dumps
core:

``` <!---c-->
    main;
```

Unless you specify `-fwritable-strings` (see `COTHER` in the example
Makefile, described in the
FAQ on "[What are the detailed recommendations for a submission
Makefile](../faq.html#makefile_details)"), do not
assume this sort of code will work:

``` <!---c-->
    char *T = "So many primes, so little time!";
    ...
    T[14] = ';';    /* modifying a string requires: -fwritable-strings */
```

Even so, one should probably not assume that this is universally
accepted.

Initialized char arrays are OK to write over.  For instance, this is
OK:

``` <!---c-->
    char b[] = "Is this OK";
    b[9] = 'k';     /* modifying an initialized char array is OK */
```


Jump to: [top](#)


<div id="likes">
<div id="dislikes">
## Our Likes and Dislikes
</div>
</div>

We **VERY MUCH LIKE** submissions that use an edited variant of the
example `Makefile`, as described and linked to in the
FAQ on "[What are the detailed recommendations for a submission
Makefile?](../faq.html#makefile_details),
renamed as `Makefile` of course.

This makes it easier for the [Judges](../judges.html) to test your
submission. And if your submissions wins, it makes it easier to
integrate it into the [Official IOCCC winner
website](https://www.ioccc.org/index.html).

We **VERY MUCH LIKE** submissions that have some educational value.
This does **NOT** mean that your submission should not be obfuscated
but rather that the IOCCC has moved away from the idea of "spoilers".
You should not encrypt or rot13 content in your `remarks.md` file.

The above statement does not mean encryption/decryption tools will not
win, nor does it mean that if you have such a submission that you could
not encrypt some remarks (such as obfuscation details), but if you do
so please put them in a separate file and indicate how to decipher it.
Please do **NOT** use any cipher to encrypt your `remarks.md`.

It is **VERY MUCH** appreciated if your remarks or `prog.c` have some
educational value. And although educational value is not required, it
is an **EXCELLENT** bonus.

We **LIKE** submissions that use an edited version of the `try.sh`
example script (and if you have alternate code, the same applies with
the `try.alt.sh` script):

- [view example try.sh](%%REPO_URL%%/next/try.sh)
- <a href="try.sh">download example try.sh</a>

- [view example try.alt.sh](%%REPO_URL%%/next/try.alt.sh)
- <a href="try.alt.sh">download example try.alt.sh</a>

Of course, it is quite possible that only one invocation is possible,
so it is not necessarily detrimental to your submission if you do not
include one, though we do like interesting and creative uses of
submissions. See also the FAQ on "[submitting try.sh and try.alt.sh
scripts](../faq.html#try_scripts)".


<p class="leftbar">
Even if it only has one invocation we still **LIKE** the try scripts
because we use them during judging and in publishing the winning
entries.
</p>

<p class="leftbar">
If you do include a `try.sh` then **PLEASE** remove the `try` rule in
the Makefile.
</p>

<p class="leftbar">
If you do include a `try.alt.sh` then **PLEASE** remove the `try.alt`
rule in the Makefile.
</p>

<p class="leftbar">
If you don't have a prog.alt.c, then **PLEASE** remove the `try.alt`
rule as well.
</p>


We tend to **DISLIKE** programs that:

* are very hardware specific
* are very OS version specific (`index(3)`/`strchr(3)` differences are
OK, but sockets/streams specific code is likely not to be)
* dump core or have compiler warnings (it is OK only if
you warn us in your `remarks.md` file)
* won't compile or run in a [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
(UNIX-like) environment
* depend on a utility or application not normally found
in systems that conform to the [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
* abuse the build file to get around the size limit
* obfuscate by use of ANSI trigraphs
* obfuscate by use of digraphs
* <p class="leftbar">obfuscate by use of `goto`s</p>
* are larger than they need to be
* have more lines than they need to have
* are "blob-ier" (just a pile of unformatted C code) than they need to be
* are rather similar to **[previous winners](../years.html)** :-(
* are **identical** to **[previous losers](https://en.wikipedia.org/wiki/Null_device)** :-)
* that mandate the exclusive use of a specific Integrated Development Environment (IDE)

In order to encourage submission portability, we **DISLIKE**
submissions that fail to build unless one is using an IDE. For example,
do not mandate that one must use Microsoft Visual Studio to compile
your submission.



Jump to: [top](#)


<div id="about-cpp">
### About C preprocessor
</div>

Doing masses of `#define`s to obscure the source has become 'old'.  We
tend to 'see thru' masses of `#define`s due to our pre-processor tests
that we apply.  Simply abusing `#define`s or `-Dfoo=bar` won't go as
far as a program that is more well rounded in confusion.

**Many** C compilers **DISLIKE** the following code, and so do we:

``` <!---c-->
    #define d define
    #d foo             /* <-- don't expect this to turn into #define foo */
```

In other words, it is a compilation error, and in order to get older
IOCCC winning entries that did this to compile, we had to update them
to not do this.

When declaring local or global variables, you should declare the type:

``` <!---c-->
    int this_is_fine;
```

and **NOT** like this:

``` <!---c-->
    this_is_not;       /* <-- Try to avoid implicit type declarations */
```

We really **DISLIKE** submissions that make blatant use of `#include`
of large data files to get around the source code size limit. This does
not mean `#include` of standard header files, just files you provide,
or system files such as `/usr/share/dict/words`.

On 28 January 2007, the Judges rescinded the requirement that the `#`
in a C preprocessor directive must be the 1st non-whitespace byte.


<div id="about-compilers">
### About compilers
</div>

We tend to **like _less_** a submission that requires either `gcc`
**OR** `clang`.  **We _prefer_ submissions** that can compile under
**BOTH** `gcc` **AND** `clang`. **Hint!**

We **RECOMMEND** that the compiler flags you use in your submission's
`Makefile` are supported by **BOTH** `gcc` **AND** `clang`.

We **DISLIKE** the use of obscure compiler flags, especially if `gcc`
and/or `clang` do not support it.  We **suggest** that you not use any
really obscure compiler flags if you can help it.


<div id="about-nested-functions">
<div id="nested-functions">
### About nested functions
</div>
</div>

One side effect of the above is that you cannot assume the use of
nested functions such as:

``` <!---c-->
     int main() {
|        void please_dont_submit_this() {
|           printf("The machine that goes BING!!\n");
         }
|        please_dont_submit_this();
     }
```

On 2012 July 20, the [Judges](../judges.html) rescinded the
encouragement of nested functions.  Such constructions, while
interesting and sometimes amusing, will have to wait until they are
required by a C standard that are actually implemented in **BOTH**
`gcc` **AND** `clang`.

We **DISLIKE** submissions that require the use of
`-fnested-functions`.


<div id="about-variadic-functions">
### About variadic functions
</div>

If your submission uses functions that have a variable number of
arguments, **be careful**. Systems implement `va_list` in a wide
variety of ways.  Because of this, a number of operations using
`va_list` **are not portable and _must not_ be used**:

* assigning a non-`va_list` variable to/from a `va_list` variable
* casting a non-`va_list` variable into/from a `va_list` variable
* passing a `va_list` variable to a function expecting a non-`va_list` arg
* passing a non-`va_list` variable to a function expecting a `va_list` arg
* performing arithmetic on `va_list` variables
* using `va_list` as a structure or union

In particular, do not treat `va_list` variables as if they were a `char
**`.

We **DISLIKE** the use of `varargs.h`.  Use `stdarg.h` instead.


<div id="about-io">
### About I/O functions
</div>

We **DISLIKE** the use of `gets(3)`.  Use `fgets(3)` instead.


<div id="about-tarballs">
### About tarballs
</div>

We tend to **DISLIKE** the blatant use of tarballs in an attempt to
simply get around the extra file number limit. We realize there may be
cases where a tarball containing a number of extra files may be needed.
Such a need for a tarball **MUST** be explained in the `remarks.md`
file.

<div id="gotos">
<div id="goto">
### On `goto`s
</div>
</div>

<p class="leftbar">
Using a mass of `goto`s to obfuscate your code has become _old_ and is
unlikely to make it through the final rounds, if it even gets that far.
</p>


<div id="about-stdib">
<div id="about-exit">
### About `exit(3)`
</div>
</div>

The `exit(3)` function returns `void`.  Some broken systems have
`exit(3)` return `int`; your submission should assume that `exit(3)`
returns a `void`.


<div id="small">
### What it means to be small
</div>

Small programs are best when they are short, obscure and concise.
While such programs are not as complex as other winners, they do serve
a useful purpose: they are often the only program that people attempt
to completely understand.  For this reason, we look for programs that
are compact, and are instructional.

Programs that claim to be the smallest C source that does something, really
better be the smallest such program or they risk being rejected because
they do not work as documented.

We suggest that you avoid trying for the '**smallest self-replicating**'
source.  The smallest, a [zero byte entry](../1994/smr/index.html), won in
[1994](../years.html#1994).

<div id="one-liner">
## What a one-liner means
</div>

One line programs should be short one line programs: say around **80**
to **132** bytes long.  Going well beyond **132** bytes is a bit too
long to be called a one-liner in our vague opinion.
<div id="blobs">
## About blobs of code
</div>

We want to get away from source that is simply a compact blob of
bytes. **REALLY TRY** to be more creative than blob coding. **HINT!**

Unless you are cramped for space, or unless you are entering the
'**Best one liner**' category, we suggest that you format your program
in a more creative way than simply forming excessively long lines.

<div id="size">
## About size restrictions
</div>

The `Makefile` should not be used to try and get around the size limit.
It is one thing to make use of a several `-D`s on the compile line to
help out, but it is quite another to use many bytes of `-D`s in order
to try and squeeze the source under the size limit.

Please do not use things like `gzip(1)` to get around the size limit.
This was done years ago; please try to be much more creative.

Your source code, post-pre-processing, should not exceed the size of
[Microsoft Windows](https://en.wikipedia.org/wiki/Microsoft_Windows).
:-)


<div id="about-environment">
### About environment
</div>

The program must compile and link cleanly in a [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
(UNIX-like) environment. Therefore do not assume the system has a
[windows.h](https://en.wikipedia.org/wiki/Windows.h) include file:

``` <!---c-->
    #include <windows.h>  /* we DISLIKE this */
```

Other windows, on the other hand, might be OK: especially where "**X
marks the spot**". Yet on the third hand, windows are best when they
are "unseen" (i.e., not dirty). :-)

<p class="leftbar">
You should try to restrict commands used in the build file to commands
found in [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
(UNIX-like) environments and systems that conform to the [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification).
</p>

You may compile and use your own programs.  If you do, try to build and
execute from the current directory.  This restriction is not a hard and
absolute one.  The intent is to ensure that the building of your
program is reasonably portable.

We prefer programs that are portable across a wide variety of UNIX-like
operating systems (e.g., Linux, GNU Hurd, BSD, UNIX, macOS, etc.).

We prefer code that can run on either a 64-bit or 32-bit processor.
However, it is **UNWISE **to assume it will run on an some Intel-like
x86 architecture**.

While programs that only run in a specific word size are OK, if you
have to pick, choose a 64-bit word size.

If your submission **MUST** run only on a 64-bit or 32-bit
architecture, then you **MUST** specify the `-arch` on your command
line (see `ARCH` in the example Makefile, described in the FAQ on
"[What are the detailed recommendations for a submission
Makefile?](../faq.html#makefile_details).

Do not assume a processor word size without specifying `-arch`.  For
example:

``` <!---make-->
    ARCH= -m64
```

Note, however, that some platforms will not necessarily support some
architectures. For instance, more recent versions of `macOS` do **NOT**
support 32-bit, and more than zero Judges use it!



<div id="about-x">
### About X
</div>

X client submissions should be as portable as possible.  Submissions
that adapt to a wide collection of environments will be favored.

For example, don't depend on a particular type or size of display.

Don't assume the use of a particular browser.  Instead assume a generic
browser that forms to a widely used [W3C
standard](https://www.w3.org/standards/).

Don't assume a particular sound sub-system or video driver is installed
in the OS. Instead, make use of a well known and widely available open
source program (one that actually works) to display audio/visual data.

X client submissions should avoid using X related libraries and
software that are not in wide spread use.

As of Red Hat RHEL9.0, the X.org server is deprecated. See the FAQ on
"[Xorg deprecation](../faq.html#Xorg_deprecated)" for more details.
This does not mean that a submission using this will necessarily be
rejected, but it would be better if it can support Wayland in some way
or another.

We **DISLIKE** submissions that use proprietary toolkits such as the
`M*tif`, `Xv*ew`, or `OpenL*ok` toolkits, since not everyone has them.
Use an open source toolkit that is widely and freely available instead.

X client submissions should try to not to depend on particular items in
`.Xdefaults`.  If you must do so, be sure to note the required lines in
the your `remarks.md` file.

X client submissions should also not depend on any particular window
manager.


<div id="about-curses">
### About libcurses
</div>

One should restrict libcurses to portable features found on both BSD
and Linux curses.

<p class="leftbar">
If you do `#include <curses.h>` make **CERTAIN** you link in curses
(i.e.  `-lcurses`) and not ncurses (i.e. `-lncurses`).
</p>

Jump to: [top](#)


<div id="about_tab">
### About ASCII TAB
</div>

We **DISLIKE** the use of ASCII tab characters in markdown files, such
as in the required `remarks.md` file.

We don't mind the use of ASCII tab characters in your C code.  Feel
free to use ASCII tab characters if that suits your obfuscation needs.
If is perfectly **OK** to use tab characters elsewhere in your
submission, just not in markdown files as this tends annoy us when it
comes time to rendering your markdown content as it complicates the
process.

If you do use ASCII tab characters in your non-markdown files, be aware
that some people may use a tab stop that is different than the common 8
character tab stop.

**PLEASE** observe our [markdown guidelines](../markdown.html) when
forming your submission's `remarks.md` file.  And if your submission
contains additional markdown files, please follow those same Guidelines
for those files.

See also [Rule 4 - Required files](rules.html#rule4-required-files),
and the FAQ on "[markdown](../faq.html#markdown)".

Jump to: [top](#)

<div id="remarks">
### About remarks.md
</div>

You are better off explaining what your submission does in your
`remarks.md` file section rather than leaving it obscure for the
[Judges](../judges.html) as we might miss something and/or be too tired
to notice.

We freely admit that interesting, creative or humorous comments in your
`remarks.md` file help your chances of winning.  If you had to read so
many twisted submissions, you too would enjoy a good laugh or two.  We
think the readers of the contest winners do as well.  We do read your
`remarks.md` content during the judging process, so it is worth your
while to write a remarkable `remarks.md` file.

It is a very good idea to, in your `remarks.md` file, tell us why you
think your submission is obfuscated.  This is particularly true if your
submission has some very subtle obfuscations that we might otherwise
overlook.  **<<-- Hint!**

Anyone can format their code into a dense blob.  A really clever author
will try formatting their submission using a "normal" formatting style
such that at first glance (if you squint and don't look at the details)
the code might pass for non-obfuscated C.  Deceptive comments, and
misleading formatting, in some cases, may be a plus.  On the other
hand, a misleading code style requires more source bytes.

If you do elect to use misleading formatting and comments, we suggest
you remark on this point in your `remarks.md` where you talk about why
you think your submission is obfuscated.

If you are pushing up against the size limits, you may be forced into
creating a dense blob. Such are the trade-offs that obfuscators face!

We **LIKE** reading `remarks.md` files, especially if they contain
useful, informative, and even humorous content about your submission.
Yes, this is a **hint**. :-)

We **RECOMMEND** you put a reasonable amount effort into the content of
the `remarks.md` file: it is a required file for a reason.  :-)

Jump to: [top](#)


<div id="miscellaneous">
### Miscellaneous
</div>

While we recognize that UNIX is not a universal operating system, the
contest does have a bias towards such systems.  In an effort to expand
the scope of the contest, we phrase our bias to favor the [Single UNIX
Specification](https://en.wikipedia.org/wiki/Single_UNIX_Specification)
(UNIX-like).

You are **well advised** to submit code that conforms to the [Single
UNIX Specification Version 4](https://unix.org/version4/overview.html).

To quote the [Judges](../judges.html):

We **LIKE** programs that:

* are as concise and small as they need to be
* do something at least quasi-interesting
* are portable
* are unique or novel in their obfuscation style
* make use of a **NUMBER OF DIFFERENT TYPES OF OBFUSCATIONS!**  **<== HINT!!**
* make us laugh and/or throw up  :-)  (humor really helps!)
* make us want to eat good chocolate

Some types of programs can't excel (anti-tm) in some areas.  Your
program doesn't have to excel in all areas, but doing well in several
areas really does help.

Try to be even more creative!

If there are limitations in your submission, you are highly encouraged
to note such limitations in your `remarks.md` file.  For example if
your submission factors values up to a certain size, you might want to
state:

>   This submission factors values up
`2305567963945518424753102147331756070`.  Attempting to factor larger
values will produce unpredictable results.

The [Judges](../judges.html) might try to factor the value -5, so you
want to might state:

>   This submission factors positive values up
`2305567963945518424753102147331756070`. Attempting to factor large
values will produce unpredictable results.

However the [Judges](../judges.html) might try to also factor 0, so you
might want to state:

>   This submission factors values between 1 and
`2305567963945518424753102147331756070`.  Attempting to factor values
outside that range will produce unpredictable results.

Moreover they might try to also factor 3.5 or 0x7, or Fred, so you want
to might state:

>   This submission factors integers between 1 and
`2305567963945518424753102147331756070`.  Attempting to factor anything
else will produce unpredictable results.

You submission might be better off catching the attempt to factor bogus
values and doing something interesting.  So you might want to code
accordingly and state:

>   This submission factors integers between 1 and
`2305567963945518424753102147331756070`.  Attempting to factor anything
else will cause the program to insult your pet fish Eric.

The [Judges](../judges.html) might not have a pet fish named Eric, so
you might want to state:

>   This submission factors integers between 1 and
`2305567963945518424753102147331756070`.  Attempting to factor anything
else will cause the program to insult your pet fish Eric, or in the
case that you lack such a pet, will insult the pet that you do not
have.

When all other things are equal, a submission with fewer limitations
will be judged better than a submission with lots of limitations.  So
you might want to code accordingly and state:

>   This submission attempts to a factor value of any size provided
that the program is given enough time and memory.  If the value is not
a proper integer, the program might insult a fish named Eric.

Do not fear if you're not 100% sure of the significance of
`2305567963945518424753102147331756070` as it is not of prime
importance: or is it?  :-)

Jump to: [top](#)


<div id="mkiocccentry">
<div id="mkiocccentry_toolkit">
## Guidelines for the mkiocccentry toolkit
</div>
</div>

The [IOCCC submit server](https://submit.ioccc.org), and related
services use the **most recent version** of the [mkiocccentry
toolkit](https://github.com/ioccc-src/mkiocccentry): submissions that
package using older versions of the [mkiocccentry
toolkit](https://github.com/ioccc-src/mkiocccentry) are **LIKELY** to
be **REJECTED**!

You **REALLY SHOULD** use the latest [mkiocccentry
toolkit](https://github.com/ioccc-src/mkiocccentry) to package your
submission as submissions that use an older version are **WILL**
be **REJECTED**!

The `mkiocccentry(1)` tool runs a number of checks by way of these
[mkiocccentry toolkit](https://github.com/ioccc-src/mkiocccentry)
tools:

* `iocccsize(1)`
* `txzchk(1)`
* `fnamchk(1)`
* `chksubmit(1)`
* `chkentry(1)`

Do **NOT** use `txzchk(1)` or `fnamchk(1)` command line options that
are labelled "**for TESTING purposes**" in their respective man pages.

Do **NOT** use `fnamchk(1)` command line options that are labelled
"**for TESTING purposes**" in the `fnamchk(1)` man page.

Do **NOT** use `chksubmit(1)` command line options that are labelled
"**for the use by the Judges only**" in the `chksubmit(1)` man page.

Similarly do **NOT** use `chkentry(1)` command line options marked
"**for the use by the Judges only**" in the `chkentry(1)` man page.

To view [mkiocccentry
toolkit](https://github.com/ioccc-src/mkiocccentry) man pages, while
your current directory is the top of the source tree:

``` <!---sh-->
    man soup/man/man1/mkiocccentry.1
    man soup/man/man1/iocccsize.1
    man soup/man/man1/txzchk.1
    man test_ioccc/man/man1/fnamchk.1
    man soup/man/man1/chksubmit.1
    man soup/man/man1/chkentry.1
```

The above `man(1)` commands will show the toolkit man pages without
having to install them first.

So that you do not have to repeatedly answer all the `mkiocccentry(1)`
questions, use `mkiocccentry -a answers ...` to create a file
containing the answers you first give, and later enter `mkiocccentry -i
answers ...` to reuse those same answers.

The `mkiocccentry -A answers ...` does the same thing except that the
**answers file will be overwritten**.

The `mkiocccentry -i answers ...` will still be required to confirm
"_Yes/No_" questions.

Use `mkiocccentry -Y -i answers ...` to force a yes answers with **great
caution** because it might force a yes answer to something you do
**NOT** want, such as a change in your code that violates a detected
rule.

The `mkiocccentry -i answers ...` will still be required to confirm
"_Yes/No_" questions.  While `mkiocccentry -Y -i answers ...` will force
yes answers, use with **great caution**, because it might force a yes
answer to something you do **NOT** want.

To help with not having to repeatedly enter a UUID, put your UUID into
a file and use `mkiocccentry -u uuidfile ...`, or use `mkiocccentry -U
UUID ...` to give the `UUID` on the command line. If you also use `-a
answers` or `-A answers` the UUID will be recorded, assuming it is a
valid UUID.

If you wish to **test** that your submission passes the
`mkiocccentry(1)` tests without having to type in answers each time,
you can use the `-d` or `-s seed` option to `mkiocccentry` for the tool
to pseudo-randomly create answers for you.  For example:

``` <!---sh-->
    mkiocccentry -d workdir topdir
```

<p class="leftbar">
Do **NOT** submit a tarball formed by `mkiocccentry -d ...` **OR** by
`mkiocccentry -s seed ...` **OR** by using the `test` UUID.
</p>

<p class="leftbar">
The `mkiocccentry(1)` tool creates an `xz(1)` compressed **v7 format**
tarball using a `tar(1)` command of the form:
</p>

``` <!---sh-->
    cd workdir/UUID-slot_num && tar --format=v7 -cJf submit.UUID-slot_num.timestamp.txz UUID-slot_num
```

In many places the `mkiocccentry(1)` tool will prompt you to verify
what you input, allowing you to correct details as you go along.

<p class="leftbar">
Pressing the "_enter key_" at the `mkiocccentry(1)` tool prompts will
allow you to proceed with a default, however make sure the default is
the **CORRECT** answer.
</p>

The `mkiocccentry(1)` tool will use code from `iocccsize(1)` which
detects a number of issues (such as [Rule 2 - Size
restrictions](rules.html#rule2-size)) that you may ignore, however
ignoring such issues **comes with a SIGNIFICANT level of risk!**

Once the submission directory has been constructed the
`mkiocccentry(1)` tool will run `chksubmit(1)` to verify everything is
well, **before** forming the tarball.

Once the tarball is formed `mkiocccentry(1)` will run `txzchk(1)`,
which will also run `fnamchk(1)`, as part of its algorithm.

<p class="leftbar">
The use of `mkiocccentry -W ...` is **highly discouraged** as this may
ignore warnings about a problem that may cause your submission to be
**REJECTED!**
</p>

<p class="leftbar">
The same can be said of `mkiocccentry -Y ...` , and to a lesser extent
`mkiocccentry -y ...`: the `-y` is mostly for the test script and the
`-Y` is like `-y` but even more aggressive.
</p>

If `mkiocccentry` encounters an **error**, the program will exit and
the xz compressed tarball **will NOT be generated**: this is a
**feature, not a bug**!

If you encounter a **bug** with the [mkiocccentry
toolkit](https://github.com/ioccc-src/mkiocccentry) **PLEASE run the
`bug_report.sh` script to help us out here!**

<p class="leftbar">
While you don't have to install the [mkiocccentry
toolkit](https://github.com/ioccc-src/mkiocccentry), if you don't, in
order to run a tool outside the repo directory you will have to specify
`mkiocccentry(1)` command line options to locate required tools such as
`chkentry(1)` (`mkiocccentry -C chkentry ...`), `txzchk(1)`
(`mkiocccentry -T txzchk ...`), and `fnamchk(1)` (`mkiocccentry
-F fnamchk ...`).
</p>

<p class="leftbar">
The `mkiocccentry(1)` tool will ignore any filename or directory that
begins with a period (`.`).
</p>

<p class="leftbar">
The `mkiocccentry(1)` tool will ignore all files that begin with
`COPYING`, `COPYRIGHT`, and `LICENSE`, regardless of filename case.
</p>

<p class="leftbar">
The `mkiocccentry(1)` tool will reject any of the following files if
they are found directly under the top level directory (`topdir`):
</p>

<p class="leftbar">
* `README.md`
* `index.html`
* `prog`
* `prog.alt`
* `prog.alt.o`
* `prog.orig.c`
* filenames matching the `[0-9][0-9][0-9][0-9]_*.tar.bz2` file glob
</p>

<p class="leftbar">
The files listed in the above list are allowed to exist in
sub-directories: just **NOT** directly under the top level directory
(`topdir`).
</p>

<p class="leftbar">
The `mkiocccentry(1)` tool evaluates all filenames and directory names
in a case independent way: thus `FOO`, `Foo`, and `foo` are considered
the **SAME** file even if your filesystem doesn't do the same.
</p>

<p class="leftbar">
Having two or more filenames that differ only by case **WILL** lead to
problems because of the previous statement.
</p>

<p class="leftbar">
When the `mkiocccentry(1)` tool ignores a file, that file is **NOT**
included as part of your submission.
</p>

<p class="leftbar">
When the `mkiocccentry(1)` tool ignores a directory, that directory,
and everything under that directory is **NOT** included as part of your
submission.
</p>

<p class="leftbar">
The `mkiocccentry(1)` tool will ignore all symlinks.
</p>

<p class="leftbar">
Creating a directory directly under the top level directory (`topdir`)
that is normally considered to be a regular file, such as a directory
named `Makefile`, `prog.alt.c`, `prog.c`, `remarks.md`, `try.alt.sh`,
or `try.sh` is **NOT** a good idea and will likely cause the
`mkiocccentry(1)` tool to abort with a **fatal error**.
</p>

<p class="leftbar">
The required `Makefile` and `remarks.md` files may **NOT** be empty.
This does not mean just 0 bytes but also that it **MUST** have
**content**, and content that is relevant (e.g. a Makefile with just
comments is **NOT** allowed). However, with the exception of the
`Makefile`, the `mkiocccentry(1)` tool will **ONLY** check file size.
</p>

<p class="leftbar">
On the other hand, `chksubmit(1)` will check that `.auth.json` and
`.info.json` are valid.
</p>

<p class="leftbar">
If the optional file `try.alt.sh`, or `try.sh` exists and is an empty
file, the `mkiocccentry(1)` tool will abort with a **fatal error**.
</p>

<p class="leftbar">
If the `mkiocccentry(1)` tool encounters anything that isn't a file,
isn't a directory, and isn't a symlink (which the tool ignores), the
`mkiocccentry(1)` tool to abort with a **fatal error**.
</p>

See the
FAQ on "[How do I report bugs in an `mkiocccentry`
tool?](../faq.html#mkiocccentry_bugs)".

See [Rule 11 - Legal rule abuse](rules.html#rule11-legal-rule-abuse)
for warnings about ignoring `mkiocccentry(1)` tool warnings.

See the
FAQ on "[What is the `fnamchk` tool?](../faq.html#fnamchk)".

See the
FAQ on "[What is mkiocccentry in simple
terms?](../faq.html#about_mkiocccentry)".

See the
FAQ on "[What is the mkiocccentry tool, how do I obtain it and how do I
use it](../faq.html#mkiocccentry)".


Jump to: [top](#)


<div id="fun">
## Fun😄damental Guidelines
</div>

The reason for the times of day are so that key IOCCC events are
**calculated** to be a **fun**ctional UTC time.  :-)

At least 2 of several reasons for selecting the prime, 2503, for [Rule
2b - Net Size](rules.html#rule2b-net-size) may be found on the
["Curios!" about 2503](https://t5k.org/curios/page.php/2503.html).

The 2503 value for [Rule 2b - Net Size](rules.html#rule2b-net-size) is
a decimal anagram of the number of the kernel disk pack of one of the
judge's [BESM-6](https://en.wikipedia.org/wiki/BESM-6).

<p class="leftbar">
There may or may not be fewer than 2^7+1 reasons why these
[Guidelines](guidelines.html) seem obfuscated.
</p>

<p class="leftbar">
Excessively "_dotty"_ use of the `chksubmit(1)` or `chkentry(1)`
commands suggests that either you like silly things, or that you
[RTFS](https://en.wikipedia.org/wiki/RTFM) with some level of care.
</p>

Some people might question what actually constitutes a valid JSON file,
given the state of the "_so-called_" JSON spec. :-)

We prefer programs that do not require a fish license: crayons and cat
detector vans not withstanding.

<p class="leftbar">
This _guideline_ has a change mark at the very start of this line.
</p>

While those who are used to temperatures found on [dwarf
planets](https://science.nasa.gov/dwarf-planets/) (**yes Virginia,
dwarf planets _ARE_ planets!**), such as
[Pluto](https://science.nasa.gov/dwarf-planets/pluto/), might be able
to explain to the Walrus why our seas are boiling hot, the question of
whether pigs have wings is likely to remain a debatable point to most.

At least one judge prefers to maintain the use of the
[leap-second](https://en.wikipedia.org/wiki/Leap_second) as part of the
world's time standard.  If your code prints time with seconds, we
prefer that your code be capable of printing the time of day during a
leap-second where the value in seconds after the minute mark is **60**.

The [Judges](../judges.html), as a group, have a history giving wide
degree of latitude to reasonable submissions.  And recently they have
had as much longitudinal variation as it is possible to have on
[Earth](https://science.nasa.gov/earth/).  :-)

> You are in a maze of twisty _guidelines_, all different.

There are at least zero [Judges](../judges.html) who think that
[Fideism](https://en.wikipedia.org/wiki/Fideism) has little or nothing
to do with the Judging process.

> All generalizations are false, including this one. -- **Mark Twain**

<p class="leftbar">
There are more than about 1 typos in this very sentence.
</p>

This could be the only _guideline_ that contains the word
[fizzbin](https://en.wikipedia.org/wiki/List_of_games_in_Star_Trek#Fizzbin).

However, do you know how to play
[fizzbin](https://en.wikipedia.org/wiki/List_of_games_in_Star_Trek#Fizzbin)?
You do?!?  (Except on Tuesday?)

OK, there are actually 2 _guidelines_ that contain the word
[fizzbin](https://en.wikipedia.org/wiki/List_of_games_in_Star_Trek#Fizzbin),
unless you count this one, in which case there are 3. :-)

**NOTE**: The previous _guideline_ in this spot has been replaced by
this _guideline_:

<p class="leftbar">
You very well might not be completely prohibited from failing to not
partly misunderstand this particular _guideline_, but of course, we
could not possibly comment!  Nevertheless, you are neither prohibited,
nor are you fully or partly required to determine that this or the
previous sentence is either false and/or perhaps misleading.
Therefore, it might be wise for you to not fail to consider to not do
so, accordingly.  Thank you very much (allegedly).
</p>

Any complaints about the above _guideline_ could be addressed to the
Speaker of the House of Commons, or to the speaker of your national
parliament should you have one.

<p class="leftbar">
Please try to avoid this specific individual _guideline_, if it is at
all possible.
</p>

We believe that Mark Twain's quote:

> Get your facts first, then you can distort them as you please.

... is a good motto for those writing code for the IOCCC.

<p class="leftbar">
We do not recommend submitting [systemd](https://systemd.io) source
code to the IOCCC, if nothing else because that code is likely to
exceed [Rule 2 - Size restrictions](rules.html#rule2-size).  This isn't
to say that another highly compact and obfuscated replacement of
`init(8)` would not be an interesting submission.
</p>

<p class="leftbar">
The IOCCC size tool
[iocccsize](https://github.com/ioccc-src/mkiocccentry/blob/master/iocccsize.c)
is not an original work unless you are [Anthony C
Howe](../authors.html#Anthony_C_Howe), in which case it is original.
:-)
</p>

<p class="leftbar">
The IOCCC tarball validator
[txzchk](https://github.com/ioccc-src/mkiocccentry/blob/master/txzchk.c)
is not an original work unless you are [Cody Boone
Ferguson](../authors.html#Cody_Boone_Ferguson), in which case it is
original. :-)
</p>

<p class="leftbar">
Even so, those tools exceed the [Rule 2 - Size
restrictions](rules.html#rule2-size) so they wouldn't qualify for the
contest anyway.
</p>

<p class="leftbar">
If the [IOCCC judges](../judges.html) are feeling like it, they might
choose to compile your program for running on an Arduino or a PDP-11.
Heck, should we ever find an emulator of 60-bit CDC Cyber CPU, we might
just try your submission on that emulator as well :-)
</p>


<p class="leftbar">
With respect to [nested functions](#nested-functions), try `chkentry
-b`.
</p>


Jump to: [top](#)


<div id="more-information">
<div id="information">
# Further Reading
</div>
</div>

See the [Official IOCCC website news](../news.html) for additional
information.

For questions or comments about the contest, see [Contacting the
IOCCC](../contact.html).

**Be SURE** to review the current [IOCCC Rules and
Guidelines](index.html) as they often change year to year.  Especially
prior to submitting to the contest.

For the latest IOCCC news, follow the [IOCCC on
Mastodon](https://fosstodon.org/@ioccc).  See our FAQ on
"[Mastodon](../faq.html#try_mastodon)" for more information.

Also consider joining the [IOCCC Discord
Server](https://discord.com/invite/Wa42Qujwnw) for the latest news,
discussions about The Rules, questions for the Judges, and `C` in
general.

<hr style="width:10%;text-align:left;margin-left:0">
Jump to: [top](#)