boostsystem

Boost.System is a component of the Boost C++ Libraries that provides a portable framework for representing and propagating error conditions. It introduces a small set of types and utilities designed to unify how errors from OS calls and library operations are reported across platforms. The core entities are boost::system::error_code and boost::system::error_condition, along with the boost::system::system_error exception that carries an error_code.

The central idea is to separate the source of an error from how it is reported to the caller. error_code represents a platform-dependent error condition, while error_condition provides a portable, cross-platform view that can be compared and mapped across libraries. Boost.System defines two standard error categories: system_category, which reflects OS- or platform-specific errors, and generic_category, which corresponds to portable errno-like values. The library also allows libraries to supply their own error categories and to create error codes that can be converted to error_conditions.

Usage patterns in Boost.System emphasize both throwing and non-throwing error handling. A typical workflow is to check an error_code after a call and either handle the failure or throw boost::system::system_error if exceptions are preferred. Because many Boost libraries (notably Boost.Filesystem and Boost.Asio) use Boost.System for error reporting, it serves as a common backbone for cross-library error sharing and message formatting.

History and impact: Boost.System was developed to provide a consistent, portable error-reporting mechanism for Boost libraries and influenced later standardization efforts around std::error_code and std::system_error. It remains a lightweight, widely used component within the Boost ecosystem.