c++ - What are those two long in vtable assembly code emitted by GCC? -


this question has answer here:

i checked assembly code generated gcc following c++ code snippet.

class interface { public:  virtual int f() = 0;  virtual int g() = 0; };  class concrete : public interface { public:  virtual int f();  virtual int g(); };

seams there 2 long in each vtable, , assembly code seams doesn't use it, purpose of 2 viable?

          .globl __ztv8concrete           .const_data           .align 3   __ztv8concrete:           .long   0   <<<< thos 2 long doesn"t used.           .long   0            .long   __zn8concrete1gev           .long   __zn8concrete1fev           .globl __ztv9interface           .weak_definition __ztv9interface           .section __data,__const_coal,coalesced           .align 3   __ztv9interface:           .long   0    <<<< thos 2 long doesn"t used also.           .long   0            .long   ___cxa_pure_virtual           .long   ___cxa_pure_virtual           .section __text,__textcoal_nt,coalesced,pure_instructions           .weak_definition        ___x86.get_pc_thunk.cx           .private_extern ___x86.get_pc_thunk.

the constructor:

  __zn8concretec1ev:   lfb8:           pushl   %ebp   lcfi9:           movl    %esp, %ebp   lcfi10:           pushl   %ebx           subl    $20, %esp   lcfi11:           call    ___x86.get_pc_thunk.bx   l2$pb:           movl    8(%ebp), %eax           movl    %eax, (%esp)           call    __zn9interfacec2ev           movl    8(%ebp), %edx 2>        leal    __ztv8concrete-l2$pb(%ebx), %eax           leal    8(%eax), %eax    <<<< skip 2 two long vtable           movl    %eax, (%edx)           addl    $20, %esp           popl    %ebx

one of 2 "spaces" should rtti (the second one), other multiple inheritance (the first one). see example http://tinydrblog.appspot.com/?p=89001, or better https://stackoverflow.com/a/5712953/613130


Comments

Post a Comment

Popular posts from this blog

html - How to style widget with post count different than without post count -

i have border below li elements in wordpress widget types appropriate. element inside set block gives them nice easy click full width. the problem, when choose option "show post count" when adding widget such categories or archives displays post count plain text after tag , because tag block pushes post number text line below. whether choose show post count or not show post count still gives exact same element identifyer example "widget_categories". how style post count not on next line still keep links non post count list items full width? here's example on sidebar www.bbmthemes.com/themes/modular/blog-standard/ in order solve problem need remove display:block; for ul.widgets ul a , add in it's place line-height: 33px; what going achieve have same visual effect. what going lose doing links going work on text , not on "box". the other way out of find post count coming , make changes this. example change text count i
Read more

How to remove text and logo OR add Overflow on Android ActionBar using AppCompat on API 8? -

have researched death , cannot find answer. i have actionbar using appcompat. supporting api v7 (api v8 do). actionbar works api v11. api < v11 has problem of removing icon (and feature) actionbar without supplying overflow. big picture have app logo, app title, , 3 icons squidging same actionbar on low end phone. trying make room! i happy 1 of 2 solutions. either: a method of getting overflow functionality can retrieved pull down. (preferred) method of removing icon , text actionbar below current xml api 11+: <resources> <!-- base application theme api 11+. theme replaces appbasetheme res/values/styles.xml on api 11+ devices. --> <style name="appbasetheme" parent="theme.appcompat.light.darkactionbar"> <item name="android:actionbarstyle">@style/liteactionbarstyle</item> <item name="actionbarstyle">@style/liteactionbarstyle</item> </st
Read more

javascript - storing input from prompt in array and displaying the array -

i want take the inputs user prompt, store input in array, , display it. want take 10 inputs user using for loop. have tried do-while shown below. var givennames = new array(); var pattern = /[\w\d]{1,}/ig; do{ var name = prompt("enter names. letters , digits accepted!\nentering empty field stops asking",""); if(name && name.match(pattern)){givennames.push(name);} } while(name != ""); function displaynames(){ if(givennames.length > 0){ document.getelementbyid("list").innerhtml = "<span style='color:navy;font- weight:bold;'>given names are:<\/span><br><br>" + givennames.join("<br><br>"); } else { document.getelementbyid("list").innerhtml = "<span style='color:navy;font-weight:bold;'>nothing has been given!<\/span>"; } } how replace for loop? var givennames = new array();
Read more