3019. Presentation of "program defined classes derived from error_category" [syserr.errcat.derived] unclear and contains mistakes

Section: 22.5.2.4 [syserr.errcat.derived] Status: New Submitter: Thomas Köppe Opened: 2017-09-20 Last modified: 2017-11-09

Priority: 3

View all issues with New status.

Discussion:

The presentation of section [syserr.errcat.derived] is currently somewhat problematic:

Partial wording proposal:

  1. In 22.5.2.1 [syserr.errcat.overview] p1, change:

    -1- The class error_category serves as a base class for types used to identify the source and encoding of a particular category of error code. Classes may be derived from error_category to support categories of errors in addition to those defined in this International Standard. Such classes shall behave as specified in this subclause22.5.2.4 [syserr.errcat.derived]. [Note: error_category objects are passed by reference, and two such objects are equal if they have the same address. This means that applications using custom error_category types should create a single object of each such type. — end note]

  2. In 22.5.2.4 [syserr.errcat.derived], change:

    virtual const char* name() const noexcept override  = 0;
    

    -1- Returns: A string naming the error category.

    virtual error_condition default_error_condition(int ev) const noexcept override;
    

    -2- Returns: An object of type error_condition that corresponds to ev.

    virtual bool equivalent(int code, const error_condition& condition) const noexcept override;
    

    -3- Returns: true if, for the category of error represented by *this, code is considered equivalent to condition; otherwise, false.

    virtual bool equivalent(const error_code& code, int condition) const noexcept override;
    

    -4- Returns: true if, for the category of error represented by *this, code is considered equivalent to condition; otherwise, false.

[2017-11 Albuquerque Wednesday night issues processing]

Priority set to 3.

Jonathan to talk to Chris K and Walter about writing a paper describing the use of error_code, error_condition and defining your own.

Proposed resolution: