22 Diagnostics library [diagnostics]

22.5 System error support [syserr]

22.5.7 Class system_­error [syserr.syserr]

22.5.7.1 Class system_­error overview [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
:
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
]
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;
  };
}

22.5.7.2 Class system_­error members [syserr.syserr.members]

system_error(error_code ec, const string& what_arg);
Effects: Constructs an object of class system_­error.
Postconditions: code() == ec and string(what()).find(what_­arg) != string​::​npos.
system_error(error_code ec, const char* what_arg);
Effects: Constructs an object of class system_­error.
Postconditions: code() == ec and string(what()).find(what_­arg) != string​::​npos.
system_error(error_code ec);
Effects: Constructs an object of class system_­error.
Postconditions: code() == ec.
system_error(int ev, const error_category& ecat, const string& what_arg);
Effects: Constructs an object of class system_­error.
Postconditions: code() == error_­code(ev, ecat) and
string(what()).find(what_­arg) != string​::​npos.
system_error(int ev, const error_category& ecat, const char* what_arg);
Effects: Constructs an object of class system_­error.
Postconditions: code() == error_­code(ev, ecat) and
string(what()).find(what_­arg) != string​::​npos.
system_error(int ev, const error_category& ecat);
Effects: Constructs an object of class system_­error.
Postconditions: code() == error_­code(ev, ecat).
const error_code& code() const noexcept;
Returns: ec or error_­code(ev, ecat), from the constructor, as appropriate.
const char* what() const noexcept override;
Returns: An ntbs incorporating the arguments supplied in the constructor.
[Note
:
The returned ntbs might be the contents of what_­arg + ": " + code.message().
end note
]