ioccc/1994/schnitzi

To build:

    make all

There are two alternate versions, one that has an increased buffer size and one that uses fgets(); neither are completely functional. See below section Bugs and (mis)features for details and the Alternate code section for how to use.

Bugs and (Mis)features:

The current status of this entry is:

STATUS: uses gets() - change to fgets() if possible

For more detailed information see 1994/schnitzi in bugs.html.

To use:

    ./schnitzi < textfile

Try:

    ./try.sh

Alternate code:

These alternate versions are for those who wish to help with getting the entry to use fgets(3). See the FAQ on "gets and fgets" for why this is desired.

The first version, schnitzi.alt.c, uses fgets(3) but when fed its own code it will generate code that still uses gets(3). What's more that code will not compile. Other functionality of the alt version works fine.

The second version, schnitzi.alt2.c, has an increased buffer size but when fed its own source code it will generate code that, although it can compile but, it has the original buffer size. This is due to a comment which is explained in more detail in 1994/schnitzi in bugs.html.

Alternate build:

    make alt

Alternate use:

Use schnitzi.alt and schnitzi.alt2 as you would schnitzi above except that feeding the source code to it will not work right.

Alternate try:

    ./try.alt.sh

Judges' remarks:

Try:

    ./schnitzi < schnitzi.c

Compare the output of the program with its source. Sure the output is different, but there is more than meets the diff's eye. Can you find out why?

You might also wish to redirect the output to another file, compile it and compare how it works to the original code.

NOTICE to those who wish for a greater challenge:

If you want a greater challenge, don't read any further: just try to understand the program via the source.

If you get stuck, come back and read below for additional hints and information.

Author's remarks:

This is a program which takes any text file as input and 'flips' the input file along a diagonal running from the top left corner down to the bottom right. In other words, the first row in the file ends up written down the first column of the result, the second row is written down the second column, etc. The program is run by redirecting a file into the executable on the command line; for instance, for the file 'info', the program would be run as follows:

    ./schnitzi < info

The program generates interesting results when its source file is used as input:

    ./schnitzi < schnitzi.c

The result of this command is a program which does the exact same thing -- in other words, both the program and the "flipped" version of itself work identically (you'll need to redirect the output of the above command into a separate file and compile it). You might notice some differences in the flipped version, though. First off, a secret message becomes visible that was not visible in the original program. Also, much of the code shows up in different places in the flipped program than it appeared in the first program. My first version of this program was perfectly symmetrical along the diagonal, but I later found out there were interesting ways to break the symmetry. The best way to see this is to load both the original and flipped versions of the program into an editor and switch back and forth between them rapidly.

C tokens longer than a character (such as main()) proved difficult to use in both the original and flipped versions (after flipping, they show up as a string of single letters on successive lines). However, I found that it was possible to get around this through a few well-placed comments. An earlier version of this program used nearly every single-character token in the "shared" area; however, it proved to be too large for contest guidelines (although the code itself is only about 300 characters, the extra whitespace needed to pad it put it over the limit -- it nearly filled a 79 by 79 area, adding up to over 4000 total characters).