Defect Report #132

Submission Date: 03 Dec 93
Submittor: WG14
Source: Clive Feather
Can undefined behavior occur at translation time, or only at run time? If the former, then how does one distinguish the two cases in the C Standard?
Consider the translation unit:
/* No headers included */
int checkup()
Case 1 */
if (0)
Case 2 */
return 2 || 1 / 0;

Case 1 calls a function with a variable number of arguments without a prototype in scope. But the call is never actually executed. Now, subclause, in the first paragraph of page 41, states that this is undefined. Is it undefined to translate the code, or to execute it? The definition of undefined behavior (subclause 3.16) clearly allows the former, and subclause does not say that the undefined behavior occurs only if the call is actually executed.
On the other hand, while subclause 6.3.5 uses similar wording about division by zero, ``we all know'' that my Case 2 is strictly conforming.
So what is the answer? If undefined behavior cannot occur at translation time, why the wording in subclause 3.16? If it can, how do I distinguish the possibilities? And, by the way, what is the answer for my Case 1?
The Response to Defect Report #109 addresses this issue. The translation unit must be successfully translated.
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