I'm trying to compile a simple hello world C++ program on my MacBook Pro. I have a M3 Pro (Nov 2023) running Sequoia 15.6. The program is: #include <iostream> int main() { std::cout << "Hello World!"; return 0; } The error I get is: In file included from test.cpp:1: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/iostream:42: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ios:220: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__locale:15: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/shared_ptr.h:13: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__compare/compare_three_way.h:13: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__compare/three_way_comparable.h:12: In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__compare/common_comparison_category.h:15: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/cstddef:42:5: error: <cstddef> tried including <stddef.h> but didn't find libc++'s <stddef.h> header. This usually means that your header search paths are not configured properly. The header search paths should contain the C++ Standard Library headers before any C Standard Library, and you are probably using compiler flags that make that not be the case. 42 | # error <cstddef> tried including <stddef.h> but didn't find libc++'s <stddef.h> header. \ | ^ However, I can see stddef.h in /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/ and in /usr/local/include