Anonymous Structures in C found in Unix Kernel -

-

i have started reading lions commentary on unix v6. came across these snippets, have never seen used in c language. author provide sort of explanation, explain me happening here?

params.h :

sw 0177570 ......  struct { int integ; };

and used in unix/prf.c

if(sw->integ == 0)

explanation author

sw defined value 0177570. kernel address of read processor register stores setting of console switch register. meaning of statement clear: contents @ location 0177570 , see if zero. problem express in c. code if (sw == 0) not have conveyed meaning. sw pointer value should dereferenced. compiler might have been changed accept if (sw-> == 0) stands, syntactically incorrect. inventing dummy structure, element integ , programmer has found satisfactory solution problem.

my question how work? when compiler sees sw->integ, how associate sw anonymous structure?

iirc, ancient c compilers kept field names (such integ) in single namespace instead of creating namespace per struct type. did not distinguish between struct pointers , int pointers, every pointer has integ field corresponding first sizeof(int) bytes. since integ first value in struct , has type int, sw->integ corresponds *((int *)sw).


Comments

Post a Comment

Popular posts from this blog

ASP.NET/SQL find the element ID and update database -

-
basically i've got update query runs when click submit button. i have asp:repeater in page layer inside this <asp:repeater id="dgbookings" runat="server" onitemdatabound="itemdb"> <itemtemplate> <div class="bookingscontent"> <div class="bookingdetails" id="<%# databinder.eval(container.dataitem, "booking_ref") %>"> <p class="infotext"><%# databinder.eval(container.dataitem, "adults") %> <asp:linkbutton onclick="editdetails" text="edit..." runat="server"></asp:linkbutton></p> <p class="infotext"><asp:linkbutton onclick="submitdetails" text="submit..." runat="server"></asp:linkbutton></p> </div> </div> </itemtemplate> <asp:repeater> and outputs ...
Read more

jquery - appear modal windows bottom -

-
i have modal windows in application, work fine <div id="modal" class="modal hide fade" tabindex="-1" role="dialog" aria-labelledby="mymodallabel" aria-hidden="true"> but when modal appears, appear top of windows, , want appear bottom the application joomla 3.0! , using template of meet gavern any idea? i found solution i modified de css in bootstrap .modal.fade { top:-25%; -webkit-transition:opacity .3s linear, bottom .3s ease-out; -moz-transition:opacity .3s linear, bottom .3s ease-out; -ms-transition:opacity .3s linear, bottom .3s ease-out; -o-transition:opacity .3s linear, bottom .3s ease-out; transition:opacity .3s linear, bottom .3s ease-out; }
Read more

c++ - Compiling static TagLib 1.6.3 libraries for Windows -

-
i having super hard time compiling , using taglib 1.6.3 in qt project. i've tried can think of. taglib claims supported through cmake i'm not having luck. furthermore, i'm confused kinds of files need qt libs! i've built *.a files, *.lib, , *.dll. understand far... believe since i'm working in windows *.lib want. no matter do, end "undefined references" taglib functions try use when try compile qt project. have tried mingw32, msys, visual studio 2008, , cross-compiling windows on linux. turning nothing. what makes less sense me if compile same taglib source qt on mac (g++ think?) works fine! somewhere in windows compilation procedures have going wrong. have been smacking face on desk 30 (on , off) hours trying figure out. since qt uses mingw must compile taglib same compiler? if compile *.lib's visual studio not compatible? are *.a libraries usable in windows? (assuming mingw) i'm still trying handle on c++ stuff, after reading coun...
Read more