Catalina C++: Using headers yield error: no member named 'signbit' in the global namespace

Question

After upgrading to Catalina from Mojave, Setuping: /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk in the env.

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Answer 1

I have just got this error when trying to compile gRPC after recently upgrading to 10.15.4 and Xcode 11.4 and I started to look at all the solutions offered (here and Can't compile a C program on a Mac after upgrading to Catalina 10.15), and tried a few of them (though not trying to recreate /usr/include as that would violate the separation that Apple were trying to create) - nothing seemed to work.

I then looked closely at the actual complier invocations that the make process was producing and noticed that there was an explicit

-I/Library/Developer/CommandLineTools/SDKs/MacOSX10.15.sdk/usr/include

that was ultimately causing the includes to happen in the wrong order - removing this explicit include path allowed the compilation to succeed with a default install of catalina, Xcode and the Xcode command-line tools, as you would expect, no other tricks/compiler flags needed.