CakeMake

This is an entry for the 29th International Obfuscated C Code Contest (IOCCC29, 2025). This file was originally remarks.md.

Overview

This program produces a small textual artifact associated with a recurring annual occasion. At first glance the code appears to perform calculations related to dates or calendar formatting. Several constants and expressions hint at month-like arithmetic and offsets. The program also makes use of the standard __DATE__ macro. Running the program before studying the code is strongly recommended.

How to build and run

Build using the provided Makefile:

    make

This produces an executable named prog. Run it:

    ./prog

To customize the repeating message, define M at compile time:

    cc -DM="\"HAPPY BIRTHDAY ALICE\"" prog.c -o prog

If M is not defined, the program will not compile. The Makefile provides a default definition via the MESSAGE variable, which can be changed there directly.

Output

The output renders a small layered structure in ASCII characters, with three distinct regions from top to bottom. The topmost region is an unbordered row of repeated characters. The middle region draws from the compiler-provided __DATE__ macro, tiling it horizontally to fill a fixed-width framed band. If the program is compiled on a specific date — say, a birthday — that date will appear here, embedded in the output naturally and without any hardcoded string in the source. The lowermost framed band uses the string supplied via M, also tiled to fill the width, followed by a solid bottom border.

The macro M

M supplies a short text pattern that repeats across the lower band. The repetition is intentional. It is inspired by the continuous printed motifs found on commercial gift ribbon and wrapping paper, where a short phrase tiles seamlessly across the surface. This also makes the program naturally reusable. To pass it on as a gift for someone else, simply recompile with a new -DM= value and on the appropriate date.

Obfuscation notes

Several elements in the source intentionally resemble date or calendar arithmetic. Examples include:

• constants such as 30 and 15
• variables that suggest calendar offsets
• bit manipulation that superficially resembles month-boundary logic

This is deliberate misdirection. No string literal appears anywhere in the source. All character values are derived through arithmetic, bit manipulation, and the __DATE__ macro. The purpose of the program is therefore not apparent from casual inspection or strings(1).

There is an additional reason for the absence of string literals beyond mere style. This program was written as a surprise. The intended recipient is a programmer who will likely read the source before running it. A stray quoted string would give the game away immediately. Keeping all character values in arithmetic form is therefore load-bearing misdirection, not decoration.

By the same token, the overall appearance of the code — date arithmetic, calendar constants, __DATE__ — is designed so that a casual reader forms a plausible but wrong hypothesis about what the program does. The strings(1) output is deliberately sterile. The true output is meant to be a surprise.

Implementation notes

The program uses recursive invocation of main as its sole iteration mechanism. Each call advances a counter and emits exactly one character via putchar. Character selection is performed by a single deeply nested conditional expression. Branches produce characters derived from:

• computed integer constants
• the __DATE__ macro
• the macro M

Code size

The source was arranged to occupy exactly 255 bytes. This value was chosen deliberately. It is not a coincidence.

The name

The project is named CMake. It resembles the well-known cross-platform build tool. Here it means something else entirely: C cake make.

The Makefile completes the joke by greeting the builder with:

Happy birthday.
Eggs, flour, and sugar are ready.
Now make the cake yourself!