[ub:expr.mul.div.by.zero] Code comment does not agree with normative wording

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#9,341 opened on Sep 21, 2026 1 comment 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 2/5
Estimated time: 1-3 hours
Newbie friendliness: 78/100

Issue type: Documentation
Clarity: Clearly specified
Activity status: Active
Tech stack: cpp, tex
Domain: documentation

Research direction

Start at the [ub:expr.mul.div.by.zero] example and compare its comment with the normative wording in [expr.mul]/4 and the note in [expr.pre]/4. Correct the example so its statement about floating-point division by zero agrees with those passages, then check the linked wording for consistency.

Written by the indexing model from the issue text.

Description

ub-ifndr

[ub:expr.mul.div.by.zero]:

int main() {
  int x = 1 / 0;        // undefined behavior, division by zero
  double d = 1.0 / 0.0; // undefined behavior on systems where the range of
                        // representable values of double is [-max,+max], on systems where
                        // representable values is [-inf,+inf] this would not be undefined behavior
}

The normative wording is ([expr.mul]/4):

If the second operand of / or % is zero, the behavior is undefined ([ub:expr.mul.div.by.zero]).

That is, the behavior of 1.0 / 0.0 is undefined even on systems that have positive and negative infinity.

In addition, a note in [expr.pre]/4 (added by P3899R3 "Clarify the behavior of floating-point overflow") mentions:

If the operands are of a type that adheres to ISO/IEC 60559, division by zero is the only case where an arithmetic expression has undefined behavior ([expr.mul]).

Dominant language: TeX
Stars: 221
Forks: 813
Avg merge: 17h 45m
Merged PRs (30d): 34

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