c++ compiler not working after macOS sequoia update

It’s probably just you |-:

I have a post that covers this general topic: Investigating Third-Party IDE Integration Problems. Please run through that process and write back if you hit a snag with the Apple side of this.

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I am seeing this on my Mac which I've just upgraded to Sequoia:

$ cat hello.cpp
#include <iostream>
int main() {
  std::cout << "Hello, world!!\n";
}
$ clang hello.cpp
hello.cpp:1:10: fatal error: 'iostream' file not found
    1 | #include <iostream>
      |          ^~~~~~~~~~
1 error generated.

I have one Mac with Sonoma where this works; the above error is from my other Mac where I just installed Sequoia. I do C++ development (on multiple platforms) for a living -- the only change is my having installed Sequoia on my one Mac, whereat a hello-world C++ program no longer compiles.

After uninstall and reinstall of xcode (version 2409 reported before & after) I can compile hello-world using clang++ and g++

I am also getting same error test.cc:1:10: fatal error: 'iostream' file not found 1 | #include <iostream> | ^~~~~~~~~~ 1 error generated. make: *** [test] Error 1 while compiling from terminal, but Xcode is working