sorting element from linked list

Question

void sortlist()
{
    struct node *a;
    struct node *temp=head;

    struct node *temp1=head->next;

    while(temp!=NULL)
    {
        while(temp1->next!=NULL)
        {
            if(temp->data > temp1->data)
            {
                a->data=temp->data;
                temp->data=temp1->data;
                temp1->data=a->data;
            }
            else
            {
                temp1=temp1->next;
            }
        }
        temp=temp->next;
    }
}

//I am new to data structures.i am encountering some problem here while trying to sort elements of linked list.list does not get sorted.any help is greatly appreciated.

simonc · Accepted Answer · 2013-07-29 06:47:56Z

4

a is an uninitialised pointer so the line

a->data=temp->data;

invokes undefined behaviour. Crashing is the most likely result here as you'll try to write to memory at an undefined address that may not be writeable by your code or may be in use by another part of your program.

You could fix this by giving a the same type as temp->data instead.

void sortlist()
{
    int a; // change type to match node->data if required
    ...
            if(temp->data > temp1->data)
            {
                a=temp->data;
                temp->data=temp1->data;
                temp1->data=a
            }
    ...
}

EDIT: There is also a potential NULL dereference crash in the line while(temp1->next!=NULL). The code below shows a potential implementation of sortlist which avoids this.

void sortlist()
{
    struct node *ptr=head;
    while(ptr!=NULL) {
        struct node *next;
        if (ptr == NULL)
            return;
        next = ptr->next;
        while(next!=NULL) {
            if(ptr->data > next->data) {
                int a=ptr->data;
                ptr->data=next->data;
                next->data=a;
            }
            next = next->next;
        }
        ptr=ptr->next;
    }
}

edited Jul 29, 2013 at 6:47

answered Jul 23, 2013 at 16:40

simonc

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5 Comments

user1944441 Over a year ago

Or just make a local struct so you don't even have to deal with types.

CodeDada Over a year ago

@simonc Thanks buddy,The crash of program got solved.but still elements does not get sorted properly

simonc Over a year ago

@sujai Can you give an example of a list you have tried to sort? What was the result of calling sortlist? Was there no change in the list or did it sort the items incorrectly?

simonc Over a year ago

@sujai If the problem was that sortlist crashes for single-element lists, I've posted an updated answer that should fix this.

CodeDada Over a year ago

ther was an error on the above code , i.e , you have given next = ptr->next; code got struck when i ran this code. instead used next=next->next and it works fine ; but anyway thanks for your support buddy .

RadhaKrishna · Accepted Answer · 2013-07-23 16:49:35Z

0

I made changes in the code and add the comments for the changes

void sortlist()
{

    // struct node *a; /* this is not required. */

    /* NULL checks are required,if head is NULL,head->next will crash.*/
    if(head == NULL || head->next == NULL) return;

    struct node *temp=head;

    struct node *temp1=head->next;

    while(temp!=NULL)
    {
        while(temp1->next!=NULL)
       {

           if(temp->data > temp1->data)
           {
                /* assuming you data is integer*/
                int d=temp->data;
                temp->data=temp1->data;
                temp1->data=d;
           }
           //else /* else is not required, better to remove it.*/
           //{
                temp1=temp1->next;
           //}
       }
    temp=temp->next;
    }
}

answered Jul 23, 2013 at 16:49

RadhaKrishna

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1 Comment

CodeDada Over a year ago

@ RadhaKrishna thanks,but the elements does not get sorted properly

simonc · Accepted Answer · 2013-07-29 06:52:30Z

0

//at last i found answer to my own problem and this is the solution,thanks for your help buddies

void sortlist()
{
    struct node *temp=head;
    int s;
    struct node *temp1=temp->next;

    while(temp!=NULL)
    {
        temp1=temp->next;                       
        while(temp1!=NULL)
        {
            if(temp->data > temp1->data)
            {
                s=temp->data;
                temp->data=temp1->data;
                temp1->data=s;
            }
            temp1=temp1->next;
        }
        temp=temp->next;
    }
}

edited Jul 29, 2013 at 6:52

simonc

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answered Jul 29, 2013 at 6:39

CodeDada

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