packing - Why doesn't C++ make the structure tighter? -



packing - Why doesn't C++ make the structure tighter? -

for example, have class,

class naive { public: char a; long long b; char c; int d; };

and according testing program, a d built 1 after another, like

a------- bbbbbbbb c---dddd

- means unused.

why not c++ create tighter, like

ac--dddd bbbbbbbb

class , struct members required standard stored in memory in same order in declared. in example, wouldn't possible d appear before b.

also, architectures prefer multi-byte types aligned on 4- or 8-byte boundaries. compiler can leave empty padding bytes between class members.

you can minimize padding reordering members yourself, in increasing or decreasing size order. or compiler might have #pragma pack alternative or similar, seek minimize padding @ possible expense of performance , code size. read docs compiler.

c++ packing

Comments

Post a Comment

Popular posts from this blog

iphone - Dismissing a UIAlertView -

iphone - Dismissing a UIAlertView - i set in app purchase app, , when user taps button, purchase started. basically, tap button, , depending on speed on net connection, waiting 10 seconds until new alert view comes asking if purchase product. user tap button multiple times since nil came up, , multiple purchase alert views come up. additionally, maybe seen user app bug. in end, problem. i want alert view come spinning wheel says "loading..." when users taps purchase button. problem is, how dismiss when new alert view comes asking user if want purchase product? if ([uialertview alloc] says: @"whatever apple's alert view says") { //dismiss "loading..." alert view here } i uncertainty work, input appreciated. thanks! you need have access alertview. can this. create alertview instance var in app delegate , when want show loading initialize instance var assign property , when want dismiss phone call [alertviewinstance d...
Read more

intellij idea - Update external libraries with intelij and java -

intellij idea - Update external libraries with intelij and java - simple plenty really. i'm using apache jars, i'll create changes jar's every often. these jars listed external libs in intelij (i.e classpath looking install dir of jar's). when create changes intelij doesn't seem know new implementation. have remove jar external library , re-ad it. does know have intelij picks changes automatically ? i've done clean , rebuild project had little effect. you can go preferences -> build, execution, deployment -> build tools -> maven -> importing , check box says import maven projects automatically . in mac, can command + shift + a , come in action reimport , click on reimport maven projects . intellij-idea
Read more

javascript - send data from a new window to previous window in php -

javascript - send data from a new window to previous window in php - i have image in main.php file : <img src="..\images\image.gif" class="cur" onclick="imgwin();"> when click on image below function has called : function imgwin() { imagewin=window.open("../pages/img.php","imagewin","toolbar=no,width=500,height=200,directories=no,menubar=no,scrollbars=yes"); } this function opens img.php in new window img.php file : <html> <head> <title>upload image</title> </head> <body> <form name="imgform" method="get" action="#"> address : <input type="file" name="imgurl" size="50"> description : <input type="text" name="description" size="50"> <input type="submit" value="sumbit...
Read more