Xcode offers -std=c 20 but command line clang does not-CodePudding

I have the Xcode command line tools installed and can use clang fine for versions up to C 17. In Xcode itself, I can select C 20 in the build settings:

But when I try to compile using clang from the command line with this option:

error: invalid value 'c  20' in '-std=c  20'
note: use 'c  17' for 'ISO C   2017 with amendments' standard
note: use 'gnu  17' for 'ISO C   2017 with amendments and GNU extensions' standard
note: use 'c  2a' for 'Working draft for ISO C   2020' standard
note: use 'gnu  2a' for 'Working draft for ISO C   2020 with GNU extensions' standard

What would be the reason for this inconsistency? In case it matters:

~/ which clang  
/usr/bin/clang  
~/ clang   -v
Apple clang version 11.0.3 (clang-1103.0.32.29)
Target: x86_64-apple-darwin20.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

(I also tried clang -x c ).

CodePudding user response：

Like you have noticed, Xcode and system uses different instance of Command Line Tools. Xcode uses the one that is embedded in Xcode, and the system will use a copy located in Library/Developer/, which is not automatically upgraded along with Xcode.

Support of c 20 flag is only added for later versions of Apple Clang, which seems like the clang embedded within your Xcode does support it, but the clang install in Library/Developer does not.

To force them be the same version, you might need to download it yourself from https://developer.apple.com/download/all/?q=command line tools, and choose the version that matches your Xcode.