destroying a structue

This is a discussion on destroying a structue within the C Programming forums, part of the General Programming Boards category; I'm trying to write a linked list with structures using gcc. I have a node structure: Code: struct Node { ...

  1. #1
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    Question destroying a structue

    I'm trying to write a linked list with structures using gcc. I have a node structure:

    Code:
    struct Node
    {
         void *value;
         Node *next;
         Node *prev;
    };
    value is a pointer to some data in memory that is allocated using malloc.
    Each node is created using malloc.

    When I destroy the list i call free on every Node pointer, but the memory that value was pointing to is still there, right?
    If so, is there some sort of destructor I can use with structs?

    ...The goal is to separate the list-specific functions as much as possible and still be able to use the list for different types of data.

  2. #2
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    free() releases the memory you malloc'ed back to the OS.

    It's still in the computer, but you can't use it.

    C doesn't have destructors, but you can make a function that calls free() for you and acts like an explicitly called destructor. Like fclose.

  3. #3
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    Sorry to hijack the thread, but when you free a Node, do you also have to manually free the pointers within, such as next and prev, or does freeing the Node automatically take care of that for you?

  4. #4
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    nope. you need to explicitly call free() on every thing you malloc.

  5. #5
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    Oh right I misread your question.

    value is still there... you have to free it. But you just said that.

  6. #6
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    haha yeah i sorta realized it was easier than i thought..
    free( (*n).value );

    but that's what i get for coding at 3:30 in the morning.

  7. #7
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    even easier:

    free( n->value );

  8. #8
    C++まいる!Cをこわせ!
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    Beware of linked lists, which is the case with the struct above. You should not free the the next, previous pointers there because they keep the list together.
    So don't randomly go about freeing them, instead just free one node and tie the rest of the list together.
    Of course, if you're meant to destroy the entire list, then it's another matter.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

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