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]

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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.

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[ 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);

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Effects: Constructs an object of class system_­error.

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Postconditions: code() == ec.

string(what()).find(what_­arg) != string​::​npos.

system_error(error_code ec, const char* what_arg);

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Effects: Constructs an object of class system_­error.

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Postconditions: code() == ec.

string(what()).find(what_­arg) != string​::​npos.

system_error(error_code ec);

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Effects: Constructs an object of class system_­error.

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Postconditions: code() == ec.

system_error(int ev, const error_category& ecat, const string& what_arg);

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Effects: Constructs an object of class system_­error.

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Postconditions: code() == error_­code(ev, ecat).

string(what()).find(what_­arg) != string​::​npos.

system_error(int ev, const error_category& ecat, const char* what_arg);

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Effects: Constructs an object of class system_­error.

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Postconditions: code() == error_­code(ev, ecat).

string(what()).find(what_­arg) != string​::​npos.

system_error(int ev, const error_category& ecat);

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Effects: Constructs an object of class system_­error.

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Postconditions: code() == error_­code(ev, ecat).

const error_code& code() const noexcept;

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Returns: ec or error_­code(ev, ecat), from the constructor, as appropriate.

const char* what() const noexcept override;

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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 ]