[Kranar]

It's a common misconception that a conforming program may not engender undefined behavior. In fact this very article touches on how realloc has introduced new (and backwards incompatible) undefined behavior precisely to accommodate the POSIX standard (so that POSIX compliant implementations of C can redefine the otherwise undefined behavior however they please).

[AlotOfReading]

Can you cite that? It runs against a plain reading of the standards (both C and C++) and would be insane for the standard to allow "correct" programs to include those with undefined behavior. There was even an unadopted proposal (n853 [1]) attempting to clarify this.

While I was making sure I wasn't missing something obvious, I took a look through the rest of the WG14 proposals to see if I was somehow off in my understanding regarding translators being allowed to barf over UB anywhere in the program. There was a proposal clarifying the situation to the possible-execution understanding from upthread submitted by Victor Yodaiken (n2278 [2]), but unfortunately it was also never adopted.

[1] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n853.htm

[2] https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2278.pdf

[Kranar]

You are now mixing correct and conforming programs. Neither the C or C++ Standard mention anything involving correct programs. C uses the term conforming program and C++ uses the term well-formed program.

In C a conforming program is any program that satisfies any single conforming implementation, even if said implementation includes extensions or non-portable constructs. A strictly conforming program is a program that satisfies every conforming implementation, which implies that said program does not produce an output that depends on undefined, unspecified, or implementation defined behavior.

In C++ a well-formed program is any program that satisfies the syntax rules, diagnosable semantic rules and the one-definition rule.