Compilation errors on macOS

[csparker247]

We've been getting some reports of compilation errors on macOS related to C/C++ includes like stddef.h. I've just experienced this myself so I wanted to report what I did to fix it.

In my case, I always do the following:

• Only installed/linked the following dependencies with Homebrew: cmake clang-format doxygen git git-lfs ninja python3 qt. Everything else must be brew unlinked when you first run CMake for vc-deps and volume-cartographer. Otherwise, CMake picks up Homebrew libraries when it shouldn't. After both have successfully built, you can brew install to your heart's content.
• Installed the remaining dependencies with vc-deps to a common directory on the system so multiple projects could share the built libraries: ~/source/custom_prefix

Using this approach, I have had a working build directory for some time. However, when I attempted to a new build directory for debugging new code, I started getting compiler errors like the following:

In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/__debug:16:
/Library/Developer/CommandLineTools/SDKs/MacOSX14.0.sdk/usr/include/c++/v1/cstddef:46:5: 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.
#   error <cstddef> tried including <stddef.h> but didn't find libc++'s <stddef.h> header. \
    ^

Obviously, quite a weird error to have happen, especially since my origin build directory would compile without issue. On macOS, this sort of thing is always, always, always a dependency issue. There's either a Homebrew dependency linked that shouldn't be, or something weird has changed in the toolchain. My clue was that I recently upgraded to macOS 14 (Ventura). Having done this too many times, I know that when the system updates, so too do the SDKs and toolchains.

First, I erased my common vc-deps install and attempted to rebuilt it from scratch. This failed with an error while trying to build boost. Notably, it was also an error related to a standard library function. After first clearing my vc-deps build and install directories again, I installed/linked Boost with Homebrew, and reconfigured vc-deps with the CMake flag -DVCDEPS_BUILD_BOOST=OFF. This installed the dependencies successfully. After that, my VC builds started working again with no issues.

[csparker247]

Homebrew's VTK has updated to use Qt6, so users can use Homebrew dependencies from now on.