Path: csiph.com!x330-a1.tempe.blueboxinc.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!border3.nntp.dca.giganews.com!Xl.tags.giganews.com!border1.nntp.dca.giganews.com!nntp.giganews.com!local2.nntp.dca.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 30 May 2011 14:07:54 -0500 From: Pete Becker Organization: Roundhouse Consulting, Ltd. Newsgroups: comp.lang.c++ Date: Mon, 30 May 2011 09:07:54 -1000 Message-ID: <2011053009075475971-pete@versatilecodingcom> References: <2011053008582491296-pete@versatilecodingcom> <0221c077-9b0c-4953-9be2-71ef9298864a@t16g2000vbi.googlegroups.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: implicit promotion User-Agent: Unison/2.1.4 Lines: 55 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-xlEiZjDw1MAgSBuGrQwp1WSC7lFXFMh0Pb9PMw4Zzpb4sEYlv5RzeFT6RQMfPtk2GXsns26uthfH62C!w209bkDGAXoFEUR6tNUugiP9lgb2WhH0/NjXpLbi43OBlLa0yNoEj+JqQjI333RcGhbReu0= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 X-Original-Bytes: 3091 Xref: x330-a1.tempe.blueboxinc.net comp.lang.c++:5842 On 2011-05-30 09:01:48 -1000, Öö Tiib said: > On May 30, 9:58 pm, Pete Becker wrote: >> On 2011-05-30 02:49:08 -1000, Öö Tiib said: >> >> >> >> >> >>> On May 30, 2:45 pm, Juha Nieminen wrote: >>>> Paavo Helde wrote: >>>>>> If you write >> >>>>>> float tot = (float)sum/tally->size(); >> >>>>>> you then have a float divided by an int, 1.5. >> >>>>> Yes, for getting floating-point division one needs to cast only one >>>>> operand to a floating-point type, the other would be cast to the type of >>>>> the first automatically. In the original line from OP both operands were >>>>> cast, possibly because the original author liked symmetry or clarity. >> >>>>   Actually, if a float is divided by an int, aren't both of them cast >>>> to double first? (Not that it probably makes any difference in practice, >>>> but just pointing out.) >> >>> Most things about floating point arithmetics is implementation defined >>> so what really happens depends on platform and compiler. >> >> Not here. Read about "usual arithmetic conversions". If one argument is >> float and the other is int, the int is converted to float. > > Or into something bigger and more precise if implementation wants. Or > that is how i read the 5/10 in "usual arithmetic conversions". No, the type of the result is float. There is general license to do floating-point math at higher precision, but that doesn't affect the type of the result. void f(float); void f(double); f(1.0f/3); // calls f(float) The relevant wording is [emphasis added]: Otherwise, if either operand is float, the other *shall be* converted to float. -- Pete Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The Standard C++ Library Extensions: a Tutorial and Reference (www.petebecker.com/tr1book)