Help understanding warning messages: Upon Updating Packages

[mfherman]

In addition to installing Xcode you could try running the installer mentioned in step 2 in this post. When I upgraded to Mojave I needed to do this to compile packages successfully.

Can't install most packages on Mac

After upgrading to Mojave myself, and seeing a couple issues, I've determined two things you generally need to do to get up and running again. Both at the command line: xcode-select --install Run installer -pkg /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg -target / which has been related to a number of strange issues (including one with rcpp autocomplete and with xml2) You may need to use sudo with the second command. This stack overflow post provides a lot more detail about the missing stdlib.h header, but the second suggestion I've given here seemed to be the solution there too.