220 34272 article Path: news.gmane.org!.POSTED!not-for-mail From: Bo Persson Newsgroups: gmane.comp.lang.c++.isocpp.proposals Subject: Re: Proposal to add constructors to std::bad_alloc exception class. 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Original-Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1do5SN-0004Ct-R0 for std-proposals@isocpp.org; Sat, 02 Sep 2017 12:15:15 +0200 X-Injected-Via-Gmane: http://gmane.org/ Original-Lines: 80 Original-X-Complaints-To: usenet@blaine.gmane.org In-Reply-To: <42389eb4-97a9-4a1d-bbfb-c653ba62097f@isocpp.org> Content-Language: sv X-Original-Sender: gclcip-std-proposals@m.gmane.org X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 195.159.176.226 is neither permitted nor denied by best guess record for domain of gclcip-std-proposals@m.gmane.org) smtp.mailfrom=gclcip-std-proposals@m.gmane.org Precedence: list Mailing-list: list std-proposals@isocpp.org; contact std-proposals+owners@isocpp.org List-ID: X-Google-Group-Id: 399137483710 List-Post: , List-Help: , List-Archive: List-Subscribe: , List-Unsubscribe: , Xref: news.gmane.org gmane.comp.lang.c++.isocpp.proposals:34272 Archived-At: On 2017-09-02 01:04, Nicol Bolas wrote: > On Friday, September 1, 2017 at 3:28:44 PM UTC-4, Rich Sposato wrote: >=20 > *5.**Allowing allocators to inform callers exactly why allocations > failed.* >=20 >=20 > Allocations may fail for reasons other than the program ran out > memory. There are specialized allocators that only handle requests > for specific sizes, such as pool allocators, that could throw > exceptions if they receive requests for sizes they cannot handle. >=20 >=20 > This example shows how an allocator might throw a bad_alloc > exception with actionable information. >=20 >=20 > void * PoolAllocator::Allocate( std::size_t bytes, std::align_val_t > alignment ) >=20 > { >=20 > if ( ( bytes < minAllowedSize ) || ( maxAllowedSize < bytes ) ) >=20 > { >=20 > throw *SmartBadAllocException(* >=20 > *=E2=80=9CError! This allocator only handles allocations from 16 thro= ugh 64 > bytes in size.=E2=80=9D, __LINE__, __FUNCTION__ );* >=20 > } >=20 > if ( !IsValidAlignment( alignment ) ) >=20 > { >=20 > throw *SmartBadAllocException(* >=20 > *=E2=80=9CError! This allocator only handles alignments on 4 byte > boundaries.=E2=80=9D, __LINE__, __FUNCTION__ );* >=20 > } >=20 > void * place =3D FindPlace( bytes, alignment ); >=20 > if ( place =3D=3D nullptr ) >=20 > { >=20 > throw SmartBadAlloc( =E2=80=9CError! Unable to allocate bytes.=E2=80= =9D, >=20 > __LINE__, __FUNCTION__ ); >=20 > } >=20 > return place; >=20 > } >=20 >=20 > Unless you write an English language parser to figure out what those=20 > mean, the only "actionable" thing that can be done is by the=20 > /programmer/ (aka: spitting the message out to the log), not by the=20 > program itself. >=20 > The only way to make this detectable by the program itself is to have it= =20 > throw something other than (or more than) `bad_alloc`. None of which=20 > requires playing games with its string. Instead of parsing strings to identify a set of known reasons, we could=20 just as well have an enum failure_reason with those reasons specified. An enum value is a lot easier to copy than a string. :-) And now we are very close the the feastures already available in the=20 header . --=20 You received this message because you are subscribed to the Google Groups "= ISO C++ Standard - Future Proposals" group. To unsubscribe from this group and stop receiving emails from it, send an e= mail to std-proposals+unsubscribe@isocpp.org. To post to this group, send email to std-proposals@isocpp.org. To view this discussion on the web visit https://groups.google.com/a/isocpp= ..org/d/msgid/std-proposals/ooe0b6%24d99%241%40blaine.gmane.org. .