Solved

why memory is not freed?

Posted on 2008-10-30
8
167 Views
Last Modified: 2012-05-05
Hello group,

I was reading a book which has a nice example to start with link lists (in snippet) but I'm wondering why allocated memory is not given back to system?!
Is this an exception or is missed?

since I'm still learning I need to make sure things I'm learning here are right.

Regards,
ak

#define RECORDS 6
 

int main()

{

  struct jb {

    char actor[25];

    struct jb *next;

};
 

  char *bonds[RECORDS] =  {

     "Sean Connery",

     "David Niven",

     "George Lazenby",

     "Roger Moore",

     "Timoth Dalton",

     "Pierce Brosnan"
 

  };
 

  struct jb *first_item;

  struct jb *current_item;

  struct jb *new_item;

  int index = 0;
 

  first_item = (struct jb *)malloc(sizeof(struct jb));

  current_item = first_item;
 

  //this loop is only for feeding the structure

  while(1)

  {

    strcpy(current_item->actor, bonds[index]);

    index++;

    if (index< RECORDS)

    {

      new_item=(struct jb *)malloc(sizeof(struct jb));

      current_item->next = new_item;

      current_item       = new_item;

    }

    else {

      current_item->next = NULL;

      break;

    }

  }
 

  current_item = first_item;   /*start over*/

  index = 1;
 

  while(current_item)

  {

    printf("Structure %d: ", index++);

    printf("%s\n", current_item->actor);

    current_item = current_item->next;

  }
 

  return 0;
 

}

Open in new window

0
Comment
Question by:akohan
  • 2
  • 2
  • 2
  • +2
8 Comments
 
LVL 28

Expert Comment

by:chilternPC
Comment Utility
you hAVE TO UN-MALLOC THE MEMORY WHEN YOU HAVE FINISHED WITH IT
OTHERWISE IT WILL BE RELEASED WHEN THE PROGRAM ENDS
(SORRY CAPS ON)
0
 

Author Comment

by:akohan
Comment Utility

So, using fee() function only is enough?
e.g.


  free(first_item);
  first_item=NULL:
and etc...


0
 
LVL 53

Expert Comment

by:Infinity08
Comment Utility
>> (SORRY CAPS ON)

lol. You know you can turn it off, don't you ? ;)


akohan, dynamically allocated memory has to be explicitly free'd using free :

        http://www.cplusplus.com/reference/clibrary/cstdlib/free.html
0
 
LVL 84

Expert Comment

by:ozo
Comment Utility
if not explicitly freed, the allocated memory is given back to system when the program exits
0
Enabling OSINT in Activity Based Intelligence

Activity based intelligence (ABI) requires access to all available sources of data. Recorded Future allows analysts to observe structured data on the open, deep, and dark web.

 
LVL 53

Expert Comment

by:Infinity08
Comment Utility
>> So, using fee() function only is enough?

For every malloc, you need to have a corresponding free. So, in your case, every node in the linked list needs to be free'd.
0
 
LVL 28

Expert Comment

by:chilternPC
Comment Utility
p.s. only free the memory once you have finished using it. :-)
if you write to the memory  after you have sent it back the program will throw exeption

cool,  I like this CAPs ON CAPS off  toggle Key , although my keyboard has
stupidly marked as 'caps lock'  :-))
0
 
LVL 23

Expert Comment

by:Mysidia
Comment Utility
Actually, no.

Usually no exception will be thrown if you attempt to write to free()'d memory.
What happens in practice is far more insidious.

Writing to free()'d memory will very likely corrupt the heap, and (if you're lucky) cause your program to crash the next time you attempt to allocate or free memory.

If you are unlucky, another malloc()'  call will have assigned that memory, and you will be silently corrupting data  elsewhere in your program.


If you want to release the memory,  you should free it after you take it out of your list, and perform no further operations on removed nodes, once they are freed.

 





struct jb* temp;
 

  while(current_item)

  {

    printf("Structure %d: ", index++);

    printf("%s\n", current_item->actor);

    temp = current_item;

    current_item = current_item->next;
 

    free(temp); /* temp is no longer in the list, now free it... */

  }

Open in new window

0
 
LVL 84

Accepted Solution

by:
ozo earned 50 total points
Comment Utility
If the he value of a pointer that refers to space deallocated by a call to the free or
realloc function is used, the behavior is undefined.
0

Featured Post

How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

Join & Write a Comment

Suggested Solutions

An Outlet in Cocoa is a persistent reference to a GUI control; it connects a property (a variable) to a control.  For example, it is common to create an Outlet for the text field GUI control and change the text that appears in this field via that Ou…
This tutorial is posted by Aaron Wojnowski, administrator at SDKExpert.net.  To view more iPhone tutorials, visit www.sdkexpert.net. This is a very simple tutorial on finding the user's current location easily. In this tutorial, you will learn ho…
Video by: Grant
The goal of this video is to provide viewers with basic examples to understand and use nested-loops in the C programming language.
The goal of this video is to provide viewers with basic examples to understand how to create, access, and change arrays in the C programming language.

744 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

16 Experts available now in Live!

Get 1:1 Help Now