Cannot compile on Mac without specifying -isysroot flag

[Jonathan Wakely]

On Tue, 2 Oct 2018 at 00:51, Kyle Martin <martinky24@gmail.com> wrote:
>
> In follow up,
>
> From a Mac (also Mojave) where g++ works, g++ -v returns:
>
> $ g++ -v
> Configured with: --prefix=/Library/Developer/CommandLineTools/usr
> --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include/c++/4.2.1
> Apple LLVM version 10.0.0 (clang-1000.10.44.2)
> Target: x86_64-apple-darwin18.0.0
> Thread model: posix
> InstalledDir: /Library/Developer/CommandLineTools/usr/bin
>
> On mine (which fails), I get:
>
> $ g++ -v
> Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr
> --with-gxx-include-dir=/usr/include/c++/4.2.1
> Apple LLVM version 10.0.0 (clang-1000.11.45.2)
> Target: x86_64-apple-darwin18.0.0
> Thread model: posix
> InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
>
> Does anyone perhaps have an understanding of what it takes to reset my installation to have the proper default directories?

The gxx-include-dir path is fixed, so can't be changed. You'd need to
rebuild GCC. The prefix path is just where GCC installs itself to, and
doesn't matter. You can move the whole installation later (preserving
the directory structure) and it will still work.