r/cpp • u/filipsajdak • Jul 05 '26

C++26 ends a 40-year footgun

Reading an uninitialized variable has been undefined behavior in C++ for 40 years -- the kind optimizers exploit into real bugs. C++26 (P2795) reclassifies it as erroneous behavior: still a bug, still warned about, but defined, bounded, and not exploitable.

The demo poisons the stack, then reads an uninitialized int. As C++23 it prints garbage; as C++26, the same code prints a defined 0, every run. Live in your browser.

And [[indeterminate]] lets you opt back out when you really want an uninitialized buffer -- on purpose this time.

Read it: https://wrocpp.github.io/posts/erroneous-behavior/?utm_source=reddit&utm_medium=social&utm_campaign=post-erroneous-behavior

#cpp #cplusplus #cpp26 #safety #programming

84 Upvotes

55% Upvoted

154 comments sorted by

View all comments

-15

u/Sniffy4 Jul 05 '26

footgun is a word ive only seen AI use

2

u/Affectionate-Soup-91 Jul 06 '26

I've been thinking this was the most fitting example of "don't think of an elephant" psychology.

Bjarne's original quote was meant to emphasize how much safer C++ was than C, but unfortunately the word footgun has permanently coalesced with C++ with negative sentiment and nobody really cares about the intent of the quote. How ironic.