Learn C Programming

Lesson 1 of 8 · Undefined Behaviour, Debugging and Reading Real C

Module 16 · Undefined Behaviour, Debugging and Reading Real C

Undefined Behaviour: the Rules You Did Not Know You Were Breaking

ProReading

Kenji's game adds bonuses to scores, and he worries about overflow. So he wrote a check: if x + 1 is smaller than x, the addition must have wrapped. He tried it on the Playground with the largest int, 2147483647.

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What is inside Undefined Behaviour: the Rules You Did Not Know You Were Breaking

  1. Kenji's check, and what GCC 12 made of it
  2. Undefined behaviour is a contract with the compiler
  3. Undefined, implementation-defined, unspecified
  4. The gallery: nine promises you have met
  5. Two more deleted checks, in the listing
  6. UBSan catches it while it happens
  7. Prevent the overflow, do not detect it afterwards
  8. A binary search by hand
  9. Annex J.2: the whole list