C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Will my memory be deallocated?          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message s Guest Posted: Wed Mar 03, 2004 9:52 pm    Post subject: Will my memory be deallocated? Regarding the following pseudocode: <pseudocode> char *buffer = new char[10]; //put some values in buffer if( some_condition ) { char *temp = new char[10]; //put some values in temp delete[] buffer; buffer = temp; temp = NULL; } //continue doing stuff with buffer </pseudocode> Question: Is the "temp = NULL;" statement necessary? If it still points to what it was originally set, will that memory be deallocated when I leave the scope of that if block? Thanks, s Back to top John Harrison Guest Posted: Wed Mar 03, 2004 9:58 pm    Post subject: Re: Will my memory be deallocated? "s" <youshouldbe (AT) home (DOT) with.yourself> wrote Quote: Regarding the following pseudocode: pseudocode char *buffer = new char[10]; //put some values in buffer if( some_condition ) { char *temp = new char[10]; //put some values in temp delete[] buffer; buffer = temp; temp = NULL; } //continue doing stuff with buffer /pseudocode Question: Is the "temp = NULL;" statement necessary? If it still points to what it was originally set, will that memory be deallocated when I leave the scope of that if block? No, definitely no. Memory is allocated with new[] is deallocated using delete[], no other way. Quote: Thanks, s john Back to top Dave Guest Posted: Wed Mar 03, 2004 10:02 pm    Post subject: Re: Will my memory be deallocated? "s" <youshouldbe (AT) home (DOT) with.yourself> wrote Quote: Regarding the following pseudocode: pseudocode char *buffer = new char[10]; //put some values in buffer if( some_condition ) { char *temp = new char[10]; //put some values in temp delete[] buffer; buffer = temp; temp = NULL; } //continue doing stuff with buffer /pseudocode Question: Is the "temp = NULL;" statement necessary? If it still points to what it was originally set, will that memory be deallocated when I leave the scope of that if block? Thanks, s temp = NULL has nothing to do with deallocation. You need to specifically delete [] the address allocated in line "char *temp = new char[10];". Back to top Mike Wahler Guest Posted: Wed Mar 03, 2004 10:03 pm    Post subject: Re: Will my memory be deallocated? "s" <youshouldbe (AT) home (DOT) with.yourself> wrote Quote: Regarding the following pseudocode: pseudocode char *buffer = new char[10]; //put some values in buffer if( some_condition ) { char *temp = new char[10]; //put some values in temp delete[] buffer; buffer = temp; temp = NULL; } //continue doing stuff with buffer /pseudocode Question: Is the "temp = NULL;" statement necessary? No. (However it might be useful for testing purposes). Don't lose the value now in 'buffer', or you'll leak memory. Quote: If it still points to what it was originally set, Whether it does or not ... Quote: will that memory be deallocated when I leave the scope of that if block? No. You allocated it, you must free it. This is why you need to retain the value orignally returned by 'new' (as you've done above), whether in the original pointer or some copy of it. -Mike Back to top David Harmon Guest Posted: Wed Mar 03, 2004 11:35 pm    Post subject: Re: Will my memory be deallocated? On Wed, 3 Mar 2004 21:58:16 -0000 in comp.lang.c++, "John Harrison" <john_andronicus (AT) hotmail (DOT) com> was alleged to have written: Quote: If it still points to what it was originally set, will that memory be deallocated when I leave the scope of that if block? No, definitely no. Memory is allocated with new[] is deallocated using delete[], no other way. But don't forget std::auto_ptr etc. Back to top John Harrison Guest Posted: Thu Mar 04, 2004 8:15 am    Post subject: Re: Will my memory be deallocated? "David Harmon" <source (AT) netcom (DOT) com> wrote Quote: On Wed, 3 Mar 2004 21:58:16 -0000 in comp.lang.c++, "John Harrison" [email]john_andronicus (AT) hotmail (DOT) com[/email]> was alleged to have written: If it still points to what it was originally set, will that memory be deallocated when I leave the scope of that if block? No, definitely no. Memory is allocated with new[] is deallocated using delete[], no other way. But don't forget std::auto_ptr etc. Well no, but what does auto_ptr use to deallocate memory? Either something non-standard, or it uses delete (not delete[] of course). john Back to top Duane Hebert Guest Posted: Fri Mar 05, 2004 1:23 am    Post subject: Re: Will my memory be deallocated? "Mike Wahler" <mkwahler (AT) mkwahler (DOT) net> wrote Quote: "s" <youshouldbe (AT) home (DOT) with.yourself> wrote in message news:404653B5.D118B513 (AT) home (DOT) with.yourself... Regarding the following pseudocode: pseudocode char *buffer = new char[10]; //put some values in buffer if( some_condition ) { char *temp = new char[10]; //put some values in temp delete[] buffer; buffer = temp; temp = NULL; } //continue doing stuff with buffer /pseudocode Question: Is the "temp = NULL;" statement necessary? No. (However it might be useful for testing purposes). Or preventing possible delete from the wrong pointer. Back to top Mike Wahler Guest Posted: Fri Mar 05, 2004 7:19 pm    Post subject: Re: Will my memory be deallocated? "Duane Hebert" <spoo (AT) flarn2 (DOT) com> wrote Quote: "Mike Wahler" <mkwahler (AT) mkwahler (DOT) net> wrote "s" <youshouldbe (AT) home (DOT) with.yourself> wrote in message news:404653B5.D118B513 (AT) home (DOT) with.yourself... Regarding the following pseudocode: pseudocode char *buffer = new char[10]; //put some values in buffer if( some_condition ) { char *temp = new char[10]; //put some values in temp delete[] buffer; buffer = temp; temp = NULL; } //continue doing stuff with buffer /pseudocode Question: Is the "temp = NULL;" statement necessary? No. (However it might be useful for testing purposes). Or preventing possible delete from the wrong pointer. That's still a 'test' (delegated to operator 'delete'). But assigning NULL blindly for that only purpose imo is poor practice. One could easily be doing such a 'safe' delete, but leaving something else 'undeleted' which should have been, possibly having it 'bite' you later (e.g. assigning a new value to a pointer that's still pointing to allocated storage.) -Mike Back to top Duane Hebert Guest Posted: Sat Mar 06, 2004 12:27 am    Post subject: Re: Will my memory be deallocated? "Mike Wahler" <mkwahler (AT) mkwahler (DOT) net> wrote Quote: Or preventing possible delete from the wrong pointer. That's still a 'test' (delegated to operator 'delete'). But assigning NULL blindly for that only purpose imo is poor practice. One could easily be doing such a 'safe' delete, but leaving something else 'undeleted' which should have been, possibly having it 'bite' you later (e.g. assigning a new value to a pointer that's still pointing to allocated storage.) I don't disagree. I don't use this idiom. Just commenting on a "possible" use. 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