#undefined-behavior
3 posts tagged #undefined-behavior.
C++26 makes an uninitialized read a defined bug
Reading an uninitialized variable has been undefined behavior in C++ since the beginning, and compilers optimize on that assumption. C++26 (P2795) reclassifies it as erroneous behavior: still a bug the compiler diagnoses, but with a defined value and no licence for the optimizer to delete surrounding code. A poisoned-stack demo shows the same source printing garbage under C++23 and a defined 0 under C++26.
C++ is writing down all of its undefined behavior
The structural move at WG21 Brno was not a feature -- it was a catalogue. P3596 adds two annexes that enumerate every case of undefined behavior and every ill-formed-no-diagnostic-required corner in the standard, and P3100 turns that list into a case-by-case program to close each one for C++29. There are exactly 80 core-language UB cases, and 70% of them are memory-safety bugs.
WG21 Brno: with C++26 done, the committee turns to undefined behavior
The WG21 Brno meeting (June 8-13, 2026) was the first since C++26 was finalized, and per Herb Sutter's trip report the theme is unmistakable: catalogue and eliminate undefined behavior, push memory-safety profiles toward C++29, and finish the pieces the C++26 MVP deferred. Reflection, the headline of C++26, was not on the marquee -- and that is exactly what shipping looks like.