alloca() function

This is a discussion on alloca() function within the C Programming forums, part of the General Programming Boards category; I would like to dynamically allocate memory for nodes in a linked list. I used to use malloc() and free() ...

  1. #1
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    alloca() function

    I would like to dynamically allocate memory for nodes in a linked list. I used to use malloc() and free() afterwards, but heard lately that it's simpler (with certain limitations like running out of memory) to use alloca().

    My question is what to put inside the brackets. If this is my person:

    Code:
    typedef struct node
    {
        char name[10];
        int age;
        int id;
        struct node *next;
    } Person;
    what should this line look like

    Code:
    Person *new = alloca(???)
    I tried to put sizeof(Person) but it fails miserably

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    And by "fails miserably" you mean what, exactly?

  3. #3
    and the hat of wrongness Salem's Avatar
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    > I would like to dynamically allocate memory for nodes in a linked list.
    So what good is alloca()?
    Your list would go out of scope as soon as the function calling alloca() returned.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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    When I input name: "abc", age: "20", id: "1" the printout function returns this to the screen

    NAME: ????!?!? AGE: 1832928 ID: 29382235

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    @Salem - did I then misunderstand the purpose of alloca? Is it not suppose to do the allocating and freeing of memory instead of ... Me?

  6. #6
    and the Hat of Guessing tabstop's Avatar
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    Did you read the description of alloca?
    Code:
    DESCRIPTION
           The  alloca() function allocates size bytes of space in the stack frame
           of the caller.  This temporary space is automatically  freed  when  the
           function that called alloca() returns to its caller.

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    yes i did read it and thats what led me to believe that instead of remembering to free everything I could use alloca

  8. #8
    and the hat of wrongness Salem's Avatar
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    It saves you from having to free it, but it doesn't save you from having to think
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  9. #9
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    dang nabbit

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