How to find and provide C++ library headers for clang? - c++

Question

I've built LLVM and Clang from sources using following instruction in order to try some of the latest C++ features.
When I try to compile basic C++ program using this clang I get errors about missing basic headers:
% /usr/local/bin/clang++ -std=c++20 main.cpp
In file included from main.cpp:1:
main.cpp:3:10: fatal error: 'array' file not found
#include <array>
I similarly have brew installed clang, which works perfectly.
The instruction mentions providing C++ library headers to clang, but I don't understand:
How to locate those?
How to make sure, that they are also up to date to support latest C++ features?
I have MacOS Monterey 12.4

Answer 1

You should specify a path to the sdk for your target platform.
You can retreive this by relying on xcrun:
/usr/local/bin/clang++ -isysroot $(xcrun --show-sdk-path) -std=c++20 main.cpp
In case you want to target other platforms (in the example bellow, for iphone) you have to specify both the target triple and the path to the appropiate sdk:
/usr/local/bin/clang++ -target arm64-apple-ios -isysroot $(xcrun --sdk iphoneos --show-sdk-path) -std=c++20 main.cpp
There is also an alternative to the -isysroot option. You could set up the SDKROOT environment variable to point to the target sdk path:
export SDKPATH=$(xcrun --show-sdk-path)
/usr/local/bin/clang++ -std=c++20 main.cpp