libboost-system1.71-dev 1.71.0-6ubuntu1 (amd64 binary) in ubuntu focal

 This package forms part of the Boost C++ Libraries collection.
 .
 The Boost System library provides simple, light-weight error_code
 objects that encapsulate system-specific error code values, yet also
 provide access to more abstract and portable error conditions via
 error_condition objects. Because error_code objects can represent
 errors from sources other than the operating system, including
 user-defined sources, each error_code and error_condition has an
 associated error_category.