C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Question about size of class          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Kouisawang Guest Posted: Sat Oct 28, 2006 9:10 am    Post subject: Question about size of class Example code: -------------------------------------------------------------------------------- class Foo{ private: double a; int b; }; -------------------------------------------------------------------------------- Question here is that when member variable is of type int (require 4 bytes) and double (require 8 bytes), why the total size is 16, not 12? I used "sizeof" to check the size. Thanks in advance -O.Kittipot Back to top Salt_Peter Guest Posted: Sat Oct 28, 2006 9:10 am    Post subject: Re: Question about size of class Kouisawang wrote: Quote: Example code: -------------------------------------------------------------------------------- class Foo{ private: double a; int b; }; -------------------------------------------------------------------------------- Question here is that when member variable is of type int (require 4 bytes) and double (require 8 bytes), why the total size is 16, not 12? I used "sizeof" to check the size. Thanks in advance -O.Kittipot Padding is added according to the platform in use. Otherwise, if you had a huge container of these, your system would slow to a crawl. Don't worry about it. Back to top Alf P. Steinbach Guest Posted: Sat Oct 28, 2006 9:10 am    Post subject: Re: Question about size of class * Kouisawang: [Placing response above relevant quote] [Quoting signature] Please don't top-post, /especially/ not in the middle of an article! And please don't quote signatures. Thank you. * Kouisawang: Quote: Alf P. Steinbach wrote: * Kouisawang: Example code: -------------------------------------------------------------------------------- class Foo{ private: double a; int b; }; -------------------------------------------------------------------------------- Question here is that when member variable is of type int (require 4 bytes) and double (require 8 bytes), why the total size is 16, not 12? You mean, "require ... with my compiler". Could you clarify about the options that I have specified? What is it? Can I change its size? Nobody but you know which options you have specified, or even which compiler you're using. Thus, nobody but you know which options are available to you. However, you might look at alignment options. There might also be some option to specify the sizes of 'double' and 'int'. E.g., compiling for different environments, or some compatibility mode, or whatever. But *DO NOT* ask about compiler specific options in this group. Ask in the/an appropriate group for your compiler. -- A: Because it messes up the order in which people normally read text. Q: Why is it such a bad thing? A: Top-posting. Q: What is the most annoying thing on usenet and in e-mail? Back to top Jim Langston Guest Posted: Sat Oct 28, 2006 9:10 am    Post subject: Re: Question about size of class "Kouisawang" <KOuisawang (AT) gmail (DOT) com> wrote in message news:1162020935.153899.228800 (AT) i3g2000cwc (DOT) googlegroups.com... Quote: Alf P. Steinbach wrote: * Kouisawang: Example code: -------------------------------------------------------------------------------- class Foo{ private: double a; int b; }; -------------------------------------------------------------------------------- Question here is that when member variable is of type int (require 4 bytes) and double (require 8 bytes), why the total size is 16, not 12? You mean, "require ... with my compiler". Could you clarify about the options that I have specified? What is it? Can I change its size? And the answer is, your compiler, with the options you have specified, adds some unused space, e.g. for making access more efficient or (on some computers) possible. Some compilers let you change the alignment of variables. Sometimes, however, when you do that the code doesn't work anymore on some specific machines. I would suggest wholeheartedly not to do this, but if you're using a Microsoft comopiler, look at #pragma pack Back to top Alf P. Steinbach Guest Posted: Sat Oct 28, 2006 9:10 am    Post subject: Re: Question about size of class * Kouisawang: Quote: Example code: -------------------------------------------------------------------------------- class Foo{ private: double a; int b; }; -------------------------------------------------------------------------------- Question here is that when member variable is of type int (require 4 bytes) and double (require 8 bytes), why the total size is 16, not 12? You mean, "require ... with my compiler". And the answer is, your compiler, with the options you have specified, adds some unused space, e.g. for making access more efficient or (on some computers) possible. -- A: Because it messes up the order in which people normally read text. Q: Why is it such a bad thing? A: Top-posting. Q: What is the most annoying thing on usenet and in e-mail? Back to top Kouisawang Guest Posted: Sat Oct 28, 2006 9:10 am    Post subject: Re: Question about size of class Alf P. Steinbach wrote: Quote: * Kouisawang: Example code: -------------------------------------------------------------------------------- class Foo{ private: double a; int b; }; -------------------------------------------------------------------------------- Question here is that when member variable is of type int (require 4 bytes) and double (require 8 bytes), why the total size is 16, not 12? You mean, "require ... with my compiler". Could you clarify about the options that I have specified? What is it? Can I change its size? Quote: And the answer is, your compiler, with the options you have specified, adds some unused space, e.g. for making access more efficient or (on some computers) possible. -- A: Because it messes up the order in which people normally read text. Q: Why is it such a bad thing? A: Top-posting. Q: What is the most annoying thing on usenet and in e-mail? Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.