GCC 15 Union Initialization Change

GCC 15 Release Series Changes, New Features, and Fixes This page is a "brief" summary of some of the huge number of improvements in GCC 15. You may also want to check out our Porting to GCC 15 page and the full GCC documentation. Caveats • Support for Nios II targets, which was marked obsolete in GCC 14, has now been removed entirely. • In the AArch64 port, support for ILP32 (-mabi=ilp32) has been deprecated and will be removed in a future release. • {0} initializer in C or C++ for unions no longer guarantees clearing of the whole union (except for static storage duration initialization), it just initializes the first union member to zero. If initialization of the whole union including padding bits is desirable, use {} (valid in C23 or C++) or use -fzero-init-padding-bits=unions option to restore old GCC behavior.

A screenshot of the GCC 15 release notes shows a caveat highlighted in red: using a {0} initializer for a C or C++ union no longer guarantees that the entire union is cleared. The joke is a programmer reaction to an unexpectedly breaking compiler change, matching the uploader’s comment about recognizing oneself in the GCC 15 changelog. EN: A screenshot of the GCC 15 release notes shows a caveat highlighted in red: using a {0} initializer for a C or C++ union no longer guarantees that the entire union is cleared. The joke is a programmer reaction to an unexpectedly breaking compiler change, matching the uploader’s comment about recognizing oneself in the GCC 15 changelog.

• @ithueti / 15837 2025-04-25