WTF? Fix to "string.h not found" in macOS

OK, I love macOS but I sometimes hate the hassle when it comes to Xcode and its toolchains. Randomly I get errors like "string.h" not found... WTF?

Here is the fix. You probably have the Xcode command line tools installed; Run
open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.1X.pkg

where you want to put the right version yourself. (X = 4 for Mojave, 5 for Catalina, etc)

If you don't have the package, try deleting and re-installing the tools and re-try

sudo rm -rf /Library/Developer/CommandLineTools

xcode-select --install

If that does not work, try
sudo xcode-select -s /Applications/Xcode.app/Contents/Developer

Hope this fixes!

*** EDIT ***

Sometimes with CLion, you may get similar error. For that, the fix is rather simple. Go to Tools --> CMake --> Reset Cache and Reload Project. That's it!