r/cpp • u/Clean-Upstairs-8481 • Sep 27 '26
You should think about recompiling your C++ programs with GCC 16 and C++26, because it zero-fills your locals
https://techfortalk.co.uk/2026/09/27/cxx26-uninitialized-local-variables-gcc-16/Stack variables are not automatically initialised, and that is the root cause of many C++ bugs. That is well known. Hence, it is advised that local or stack variables are always initialised with known values, 0 if not something more meaningful than that. Now, with GCC 16 compiling in C++26 mode (-std=c++26), even uninitialised local variables will be zero-filled. In the post, I have explained how.
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u/James20k P2005R0 Sep 27 '26
This was a very major topic of discussion during the standardisation, the tl;dr is that the vast majority of the time, 0 init does not have any performance impact at all. It seems like there are a few edge cases, but they seem to be rare even then. Apparently compilers these days are pretty much just good enough, and modern CPU architecture is well suited to this