Public
Authored by Adrien Oliva

Build bug on zero

Source

https://stackoverflow.com/questions/9229601/what-is-in-c-code

Usage

Force a compilation error if condition is true, but also produce a result (of value 0 and type size_t), so the expression can be used e.g. in a structure initializer (or whereever else comma expressions aren't permitted).

Explain

sizeof(struct { int: -!!(e); }))

  • (e) compute expression e
  • !!(e) Logically negate twice: 0 if e == 0, otherwise 1
  • -!!(e) numerically negate the expression from step 2

If it was 0, then we declare a struct with an anonymous integer bitfield that has width zero. Everything is fine and we proceed as normal. On the other hand, if it is not zero, then it will be some negative number. Declaring any bitfield with negative width is a compilation error.

bug_on_zero.c 132 Bytes
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