Weekend projects: getting silly with C

Switch tricks, Duff’s device, and control‑flow abuse

• Several comments connect the article’s “switch shenanigans” to Duff’s device: exploiting fallthrough and the ability to interleave switch with loops to unroll code.
• Others argue the article’s tricks differ: more about removing angle brackets and pushing control keywords left, whereas Duff’s device is specifically a loop‑unrolling pattern.
• Some see these patterns as clever but dangerously unclear, preferring explicit goto over abusing switch.

Memory‑mapped I/O, volatile, and intrinsics

• One line of discussion criticizes treating MMIO as normal memory plus volatile, calling it a type‑system hack and a layering violation.
• The alternative proposed is platform‑specific intrinsics for MMIO operations, making constraints explicit (alignment, bit‑level writes).
• Pushback: others see volatile and even register as acceptable, with implementation‑defined behavior being natural in this domain; they consider atomics intrinsics more problematic in practice.

C learning, style, and tooling

• Multiple commenters value learning C for its closeness to hardware and as a foundation for understanding abstractions.
• Modern compilers and static analysis are said to mitigate many classic footguns (e.g., assignments in if conditions).
• Debate around “Yoda conditions” (if (1 == x)) versus relying on warnings; some consider such defensive style unnecessary and less readable.
• Comparison with Python: students gravitate to high‑level tools but may not understand underlying computation or statistics, leading to fragile code.

Undefined behavior and “time travel”

• Long subthread on whether UB can affect behavior before the UB point (“time‑traveling UB”).
• One side asserts C’s model (especially in C23) requires observable behavior before UB to remain as specified; UB cannot “go back in time.”
• Others note that compilers assume absence of UB and may optimize aggressively, sometimes appearing to remove or reorder side effects; examples with divisions by zero and volatile are discussed.
• There is disagreement over how strictly compilers conform and whether some optimizations violate the intended guarantees.

Compiler extensions and oddities

• GNU/Clang extensions highlighted: case 1 ... 10: ranges, computed gotos, ternary without middle expression.
• Unusual but standard C behaviors: 4[arr] == arr[4]; lifetime rules allowing goto to a label that uses a variable declared later in the block.
• Switch‑based macros for coroutines and for auto‑breaking cases are mentioned as real‑world but niche techniques.

Obfuscation vs everyday practice

• Several commenters stress that the most extreme examples (including IOCCC‑style code) are not used in normal C development.
• Real “C wizardry” is seen more in managing overflow, concurrency, architecture, and build systems than in syntactic tricks.