C Language, Bonehead malloc/free question

Bonehead malloc/free question

Author	Message
smills_9.. #1 / 5	Bonehead malloc/free question For example, if I have a linked list pointed to with ll_ptr, will this work o.k.? while(ll_ptr != NULL) { free((char )ll_ptr); ll_ptr = ll_ptr->next; Quote: } 2 troubling points: (1) My compiler seems to force me to cast the pointer to type char for free(char ptr) to work, (go figure - char ptr needs to be a char ). (2) pointing to the "next" after freeing the previous node seems weird. Are either of these points worth fretting over? Thanks for any input. Sent via Deja.com http://www.--.com/ Before you buy.
Tue, 31 Dec 2002 03:00:00 GMT

Jarm #2 / 5	Bonehead malloc/free question Quote: > For example, if I have a linked list pointed to with ll_ptr, will this > work o.k.? > while(ll_ptr != NULL) { > free((char )ll_ptr); > ll_ptr = ll_ptr->next; > } > 2 troubling points: > (1) My compiler seems to force me to cast the pointer to type char > for free(char ptr) to work, (go figure - char ptr needs to be a char > ). > (2) pointing to the "next" after freeing the previous node seems weird. > Are either of these points worth fretting over? > Thanks for any input. > Sent via Deja.com http://www.deja.com/ > Before you buy. 1. ll_ptr is obviously not a char so it has to be cast (if your compiler options are very picky, e.g. C++ mode) 2. it's not just weird, it's wrong and should be changed (keep a temporary copy of ll_ptr->next before freeing ll_ptr)
Tue, 31 Dec 2002 03:00:00 GMT

Mark McIntyr #3 / 5	Bonehead malloc/free question Quote: >For example, if I have a linked list pointed to with ll_ptr, will this >work o.k.? >while(ll_ptr != NULL) { > free((char )ll_ptr); > ll_ptr = ll_ptr->next; >} >2 troubling points: >(1) My compiler seems to force me to cast the pointer to type char >for free(char ptr) to work, (go figure - char ptr needs to be a char >). Your compiler is astonishingly old from the sounds of it - or worse its not a proper C compiler. Free takes a void and this would need no cast. Pre-ANSI compilers expected a char. Since ll_ptr is not a char, _you_ need the cast. Get a new compiler Quote: >(2) pointing to the "next" after freeing the previous node seems weird. What you're doing is illegal. You free the data, then access a member of it. Blammo! Find the next element BEFORE freeing the pointer... Quote: >Are either of these points worth fretting over? Yes -- Mark McIntyre C- FAQ: http://www.eskimo.com/~scs/C-faq/top.html
Tue, 31 Dec 2002 03:00:00 GMT

Richard B #4 / 5	Bonehead malloc/free question Quote: > For example, if I have a linked list pointed to with ll_ptr, will this > work o.k.? > while(ll_ptr != NULL) { > free((char )ll_ptr); > ll_ptr = ll_ptr->next; > } No. Quote: > 2 troubling points: > (1) My compiler seems to force me to cast the pointer to type char > for free(char ptr) to work, (go figure - char ptr needs to be a char > *). Have you remembered to #include <stdlib.h>? I can't think of any other decent reason to complain about that. Quote: > (2) pointing to the "next" after freeing the previous node seems weird. And is. You're invoking undefined behaviour; this _may_ work, but only by accident. The computer is quite at liberty to dump core on you from twelve feet high if you try this. You should, as you suspected, never use memory after you've freed it. Try this one: while (ll_ptr) { temp_ptr=llptr->next; free(ll_ptr); ll_ptr=temp_ptr; } Richard
Wed, 01 Jan 2003 03:00:00 GMT

Keith Thompso #5 / 5	Bonehead malloc/free question [...] Quote: > (1) My compiler seems to force me to cast the pointer to type char * > for free(char ptr) to work, (go figure - char ptr needs to be a char > ). Do you have a #include <stdlib.h>? -- San Diego Supercomputer Center <> <http://www.sdsc.edu/~kst> Welcome to the last year of the 20th century.
Wed, 01 Jan 2003 03:00:00 GMT

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