Why GCC’s Switch to C++20 Matters for Every C++ Developer

The C++ ecosystem is undergoing a major transition as the language officially enters the C++20 era. GCC, a core modern C++ compiler, has decided to make C++20 (specifically the GNU++20 dialect) the default standard, replacing the previous C++17 default.

Historically, GCC 11 switched its default from C++14 to C++17 in 2020. Earlier this month, GCC developers discussed and approved the change to C++20 without requiring an explicit flag. The change is now live: compiling C++ code with GCC will automatically use C++20 unless the developer specifies a different standard such as -std=c++17.

GCC developers acknowledge that parts of the compiler’s own codebase were not yet fully compatible with C++20, but they have been actively fixing these issues to ensure that the upcoming GCC 16 release will work flawlessly with the new default.

As of the November 19 change, the default is GNU++20, and the GCC Git repository continues to address remaining C++20‑related problems.

Although GCC 16.1 stable has entered its third development stage, the default‑standard change has already been approved, and the latest GCC Git source has been updated to reflect this modern default.

For projects that have not yet prepared for C++20 and do not explicitly set -std=c++17 (or another flag), the new default may cause build failures. Open‑source projects that regularly test with GCC Git have a few months to ensure their codebases conform to C++20 or to pin the standard to C++17 in their build systems.

Conclusion

Switching to GCC 20 will introduce new warnings and behavioral changes across codebases of any size, necessitating appropriate adjustments. This move encourages developers to adopt modern C++ idioms and take advantage of the language’s latest features.

References:

https://www.phoronix.com/news/GCC-16-Now-CPP20-Default

https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=004438857554f47eb5491d59b067e56fdacf0e74