'Error: 'no member named 'signbit' in the global namespace' After Catalina Upgrade: What's the Solution?'

Error: "no member named 'signbit' in the global namespace" After Catalina Upgrade

When upgrading to macOS Catalina from Mojave, users have encountered an error when compiling programs using the header:

error: no member named 'signbit' in the global namespace

This error stems from the fact that Catalina purges and protects /usr/include with System Integrity Protection (SIP). Therefore, any projects that expect to find C headers in this directory will fail to compile.

Solution:

To resolve this issue, it is necessary to direct the build system to the appropriate headers:

1. Ensure Xcode is Updated: Use the latest version of Xcode to avoid potential incompatibilities.

2. Set CMAKE_OSX_SYSROOT: Set this variable to the result of xcrun --show-sdk-path using one of the following methods:

   • set(CMAKE_OSX_SYSROOT /sdk/path)
   • set(CMAKE_CXX_FLAGS "[...] -isysroot /sdk/path")

If these steps resolve the problem, consider exploring better approaches for setting these flags in CMake. Additionally, disabling SIP (although adventurous) may provide a temporary solution. However, it is recommended to report bugs to projects that still expect C headers in /usr/include.

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