Thread: Function which insert one Node in a List

  1. #1
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    Function which insert one Node in a List

    Hi everybody,

    I'm writing this post because I can't understand a function, which is thought to insert a node at the beginning of a linked list.

    Here we have the function:

    void pre_insert(struct list ** doubleptr, float value);

    Code:
    void pre_insert(struct list ** doubleptr, float value) { 
    /*INPUT of the function:
    -pointer which points to a pointer which points to a record;
    -float.*/
    
    struct list * temporary; /*I create a pointer to a record*/
    
    
        temporary = *doubleptr; /*The pointer I created point to the pointer
    pointed by the doublepointer of the input*/
    
    
        *doubleptr = (struct list *)malloc(sizeof(struct list)); /*I create a new record, 
    I give his adress to the double pointer of the input*/
    
    
        (*doubleptr)->value = value; /*I can't understand what happen here*/
        (*doubleptr)->next_ptr = temporary;/*I can't understand what happen here*/
        }

    Can anyone tell me:
    - if the sentences written as comments are correct;
    - what happen in the last two lines.
    Thank a lot!!!
    Last edited by letthem; 06-24-2019 at 03:04 PM. Reason: Font size abuse

  2. #2
    and the hat of int overfl Salem's Avatar
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    Well you are going about it backwards.

    Naming all your variables 'tmp' and 'ptr' doesn't add any clarity either.

    Code:
    void pre_insert(struct list **head, float value) { 
        struct list *newnode = malloc(sizeof(*newnode));
        newnode->value = value;
        newnode->next = *head;
    
        *head = newnode;
    }
    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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