C++ : How can I know the size of Base class SubObject? -


.

here discussing empty base optimization, , msalters made interesting comment:

no class can ever have sizeof(class)==0, empty or not. but we're talking on size of empty base class subobject. doesn't need own vtable, nor vtable pointer. assume common layout of vtable pointer @ offset 0; cause zero-sized base class subobject share vtable pointer derived class. no problem: should identical anyway, that's pretty point of virtual functions.

my question this: compiler may optimize when use empty class base class, or may not. how determine does?

and in general, how can know size of base class subobject? size of base subobject same irrespective of whether use base or not? compilers optimize empty base classes?

.

good answers.

by way, ms vc++ , g++ compilers can dump class layouts study.

with vc++ run cl.exe /c /d1reportallclasslayout <source>.cpp

this uses class , vtable layout dump code wrote in 1990 test proper layout objects, vtables, vbtables, etc.

to better understand how c++ compilers lay out objects in memory, might enjoy http://www.openrce.org/articles/files/jangrayhood.pdf , stan lippman's book inside c++ object model.

happy hacking!


Comments

Post a Comment

Popular posts from this blog

asp.net - repeatedly call AddImageUrl(url) to assemble pdf document -

i'm using abcpdf , i'm curious if can recursively call addimageurl() function assemble pdf document compile multiple urls? something like: int pagecount = 0; int theid = thedoc.addimageurl("http://stackoverflow.com/search?q=abcpdf+footer+page+x+out+of+", true, 0, true); //assemble document while (thedoc.chainable(theid)) { thedoc.page = thedoc.addpage(); theid = thedoc.addimagetochain(theid); } pagecount = thedoc.pagecount; console.writeline("1 document page count:" + pagecount); //flatten document (int = 1; <= pagecount; i++) { thedoc.pagenumber = i; thedoc.flatten(); } //now try again theid = thedoc.addimageurl("http://stackoverflow.com/questions/1980890/pdf-report-generation", true, 0, true); //assemble document while (thedoc.chainable(theid)) { thedoc.page = thedoc.addpage(); theid = thedoc.addimagetoc
Read more

java - Android recognize cell phone with keyboard or not? -

in android app, want detect user's device if device has keyboard(like motorola milestone) , show corresponding user interface. guys know how that? ! regards justicepenny http://developer.android.com/reference/android/content/res/configuration.html public int keyboard the kind of keyboard attached device. 1 of: keyboard_nokeys, keyboard_qwerty, keyboard_12key. that's it!
Read more

iphone - How would you achieve a LED Scrolling effect? -

how achieve led scrolling effect example below? led sign - led ticker emulator iphone , ipad http://img.skitch.com/20101201-rsfh4p1bajb1wp94k466pdpiuj.preview.jpg sometimes remunerates comment in other posts :) have put code you, should implement font '8pin matrix' realistic feeling. uilabel *label; - (void)viewdidload { [super viewdidload]; label = [[uilabel alloc]initwithframe:cgrectmake(10, 50, 300, 20)]; label.font = [uifont fontwithname:@"courier-bold" size:16.0]; label.backgroundcolor = [uicolor blackcolor]; label.textcolor = [uicolor greencolor]; label.linebreakmode = uilinebreakmodecharacterwrap; // otherwise "…" label.text = @"this led text scrolled "; // blanks space between [self.view addsubview:label]; [nstimer scheduledtimerwithtimeinterval:0.12f target:self selector:@selector(scrolllabel) use
Read more