[syserr.syserr.overview]

The class system_error describes an exception object used to report error conditions that have an associated error code.

Such error conditions typically originate from the operating system or other low-level application program interfaces.

[Note 1:

If an error represents an out-of-memory condition, implementations are encouraged to throw an exception object of type bad_alloc rather than system_error.

— end note]

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namespace std { class system_error : public runtime_error { public: system_error(error_code ec, const string& what_arg); system_error(error_code ec, const char* what_arg); system_error(error_code ec); system_error(int ev, const error_category& ecat, const string& what_arg); system_error(int ev, const error_category& ecat, const char* what_arg); system_error(int ev, const error_category& ecat); const error_code& code() const noexcept; const char* what() const noexcept override; }; }