Doc. No.:  X3J16/96-0200
                                           WG21/N1018
                                Date:      November 7, 1996
                                Project:   Programming Language C++
                                Reply To:  Sandra Whitman
                                           Digital Equipment Corporation
                                           whitman@tle.enet.dec.com
 
 
Clause 19 (Diagnostics Library) Issues List - Version 3
 
Revision History
 
Version 1 - May 22, 1996:       Distributed in pre-Stockholm mailing.
Version 2 - July 15, 1996:      Distributed in post-Stockholm mailing.
Version 3 - November 7, 1996:   Distributed in pre-Hawaii mailing. 
 
Introduction
 
This document is a summary of the issues identified in Clause 19.  For
each issue the status, a short description, and pointers to relevant
reflector messages and papers are given.  
 
 
Active Issues
-------------------------------------------------------------------------
 
Work Group:     Library Clause 19
Issue Number:   19-002
Title:          Derived exception classes in <stdexcept> are broken.
Sections:       19 Diagnostics Library [lib.diagnostics]
Status:         active
Description:    Kevlin Henney in c++std-lib-4925:

    >As currently specified all the derived exception classes in 
    ><stdexcept> are broken. Consider:
    >
    >    try
    >    {
    >        throw logic_error("undefined behaviour");
    >    }
    >    catch(logic_error &ex)
    >    {
    >        cerr << ex.what() << endl;
    >    }
    >
    >The string passed to logic_error is a temporary that is destroyed as the
    >stack unwinds. No surprises there, except that the postcondition for all
    >the exceptions in <stdexcept> states
    >
    >    "Postcondition: what() == what_arg.data()"
    >
    >Implying an implementation of
    >
    >    class logic_error
    >    {
    >    public:
    >        logic_error(const string& what_arg) : ptr(what_arg.data()) {}
    >        virtual const char *what() const { return ptr; }
    >    private:
    >        const char *ptr;
    >    };
    >
    >Clearly (I hope) string content equality rather than pointer equality was
    >intended:
    >
    >    "Postcondition: strcmp(what(), what_arg.c_str()) == 0"
    > 
    >As an aside, it seems that an implementation is not entitled to add any
    >extra info (eg. "logic_error: " prefix), which in some ways is a shame.

Proposed Resolution:

    Change Postcondition sections in 19.1.1 [lib.logic.error],
    19.1.2 [lib.domain.error], 19.1.3 [lib.invalid.argument],
    19.1.4 [lib.length.error], 19.1.5 [lib.out.of.range], 
    19.1.6 [lib.runtime.error], 19.1.7 [lib.range.error],
    19.1.8 [lib.overflow.error], 19.1.9 [lib.underflow.error]

    from: Postcondition: what() == what_arg.data() 
    to:   Postcondition: strcmp(what(), what_arg.c_str()) == 0
 
Requestor:      Kevlin Henney, Kevlin@two-sdg.demon.co.uk
Owner:          Sandra Whitman
Emails:         c++std-lib-4925.
Papers:         None.


Closed Issues
-------------------------------------------------------------------------

Issue Number: 19-001
Title:        Use and Treatment of Clause 19 Predefined Exceptions Inconsistent
Last Doc.:    N0936R1=96-0118R1
Resolution:   closed, no action (Stockholm)