C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Question on static and dynamic memory allocation          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message KK Guest Posted: Fri Nov 19, 2004 3:37 pm    Post subject: Question on static and dynamic memory allocation Greetings, I am trying to undersand the process of static and dynamic memory allocation for a two dimensional array. /* Example to illustrate the processes of memory allocation of a two dimensional array */ #include<iostream> using namespace std; int main(){ /*Static memory allocation */ cout<<"Case : static array allocation:n"; char A[2][3]; cout<<"&A["<<0<<"] = "<<(void *)(&A[0])< cout<<"A[0] ="<<(void *)A[0]< /*Dynamic memory allocation */ cout<<"Case : dynamic array allocation:n"; char **B=new char*[2]; for(int i = 0; i < 2; i++) B[i]= new char[3]; cout<<"&B["<<0<<"] = "<<(void *)(&B[0])< cout<<"B[0] ="<<(void *)B[0]< return 0; } The output of the program is as follows, Case : static array allocation: &A[0] = 0012FF78 A[0] = 0012FF78 Case : dynamic array allocation: &B[0] = 00320930 B[0] = 00320968 As you might have observed &A[0]==A[0] (static case) where as &B[0]!=B[0](dynamic case). Could anyone kindly reason out this inconsistent behaviour? Thank you in advance, -KK [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top jjr2004a Guest Posted: Tue Nov 23, 2004 10:45 am    Post subject: Re: Question on static and dynamic memory allocation [email]kewlkarun (AT) yahoo (DOT) com[/email] (KK) wrote in message news:<c8fd5039.0411182132.1aab5b9f (AT) posting (DOT) google.com>... Quote: Greetings, I am trying to undersand the process of static and dynamic memory allocation for a two dimensional array. /* Example to illustrate the processes of memory allocation of a two dimensional array */ #include<iostream using namespace std; int main(){ /*Static memory allocation */ cout<<"Case : static array allocation:n"; char A[2][3]; cout<<"&A["<<0<<"] = "<<(void *)(&A[0])< cout<<"A[0] ="<<(void *)A[0]< /*Dynamic memory allocation */ cout<<"Case : dynamic array allocation:n"; char **B=new char*[2]; for(int i = 0; i < 2; i++) B[i]= new char[3]; cout<<"&B["<<0<<"] = "<<(void *)(&B[0])< cout<<"B[0] ="<<(void *)B[0]< return 0; } The output of the program is as follows, Case : static array allocation: &A[0] = 0012FF78 A[0] = 0012FF78 Case : dynamic array allocation: &B[0] = 00320930 B[0] = 00320968 As you might have observed &A[0]==A[0] (static case) where as &B[0]!=B[0](dynamic case). Could anyone kindly reason out this inconsistent behaviour? Thank you in advance, The behavior is not inconsistent at all. By taking a look at how the memory is laid out you can see why. A is an array of six characters laid out in contiguous memory like this: +-+-+-+-+-+-+ Quote: 0|1|2|3|4|5| +-+-+-+-+-+-+ B is slightly more complicated layout. It consists of space for three pointers and space for six characters which are not contiguous. B B[0] +-+ +-+ +-+-+-+ Quote: *--->|*--->|0|1|2| +-+ +-+ +-+-+-+ +-+-+-+ *------------>|3|4|5| +-+ +-+-+-+ B[1] From this layout you can deduce that B == &B[0], B[0] == &B[0][0] and B[1] == &B[1][0] by definition. This is really a C question. I've found the book "Advanced C Tips and Techniques", by Kochan & Wood explains this stuff in depth. It may be out of print but they seem to have a website and it may be available from there for download. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] 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 (Moderated) 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.