Why is 'signbit' Missing from After Upgrading to Catalina?

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Catalina C : Dealing with the "signbit" Error in

In the wake of upgrading from Mojave to Catalina, users may encounter compilation issues when referencing the header in C programs. This problem manifests itself as errors pertaining to the absence of "signbit" in the global namespace.

Initially, attempts to modify the CFLAGS, CCFLAGS, and CXXFLAGS environment variables appear to yield no results. However, upon closer examination, the root cause of the issue lies elsewhere.

The Role of CMAKE_OSX_SYSROOT

The value of CMAKE_OSX_SYSROOT plays a pivotal role in this issue. By default, it points to an incorrect location after upgrading to Catalina. This misconfiguration results in the build system using the wrong header files, which lack the necessary definitions.

Solution: Setting the Correct CMAKE_OSX_SYSROOT

To rectify the situation, it is essential to manually specify the proper path to the SDK headers. This can be achieved by employing the following steps:

1. Ensure that Xcode is up to date to avoid potential compatibility issues.
2. Utilize the xcrun --show-sdk-path command to determine the correct SDK path.
3. Modify the CMake configuration as follows:

set(CMAKE_OSX_SYSROOT /sdk/path)

Alternatively, you can set the -isysroot flag directly for the CXX compiler:

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

Conclusion

By addressing the improper setting of CMAKE_OSX_SYSROOT, you can successfully resolve the error related to "signbit" and continue developing C programs with in the Catalina environment.

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