Checklist: Transition to C17 as the minimum required C standard version

[carlescufi]

Summary

This task tracks the transition from C99 to C17 as the minimum required C standard version in order to compile Zephyr applications. This started originally as an RFC in #30105.

The TSC discussed this on the 30th of April 2025, the minutes can be found here.
An email was then sent out to the devel mailing list.

Checklist

Toolchains

The following toolchains have been checked to verify if they provide complete or near-complete C17 support:

• ✅ GCC (See C language)
• ✅ Clang/LLVM (See C Support in Clang)
• ✅ IAR (See this comment)
• ✅ Arm Toolchain for Embedded (based on Clang/LLVM, see releases)
• ✅ Synopsys Metaware (MWDT, based on Clang/LLVM)
• ❌ Cadence 2017 (based on GCC 4.4.x)
• ✅ Cadence 2022 (based on Clang/LLVM 10.x)

C standard libraries

• ✅ Minimal libc (compiles, but doesn't offer the features)
• ✅ Picolibc (confirmed by maintainer @keith-packard)
• newlib ?

Pull Request

The PR that transitions to C17 by default is #97076

[nordicjm]

Looks like nanopb has problems with this @pdgendt #97076

[pdgendt]

Looks like nanopb has problems with this @pdgendt #97076

See my comment here: #97076 (review)

[nashif]

need data from mwdt and cadence based toolchains used by many platforms.

[carlescufi]

need data from mwdt and cadence based toolchains used by many platforms.

Who can provide that @nashif ?

[nashif]

need data from mwdt and cadence based toolchains used by many platforms.

Who can provide that @nashif ?

@ruuddw @kv2019i ^^