double free or corruption (fasttop)

Question

The following section of my code gives me this messege when executing * glibc detected ./a.out: double free or corruption (fasttop): 0x08e065d0 **

i have gone through the code many times but i cant clealry see how i am misusing the free (temp2)

bool found= false;
int x=0;
for ( x=0; x<=312500; x++)
{
    while (count <=32)
    {
        fscanf (file, "%d", &temp->num);  

        temp->ptr=NULL;

        newNode = (NODE *)malloc(sizeof(NODE));
        newNode->num=temp->num;
        newNode->ptr=NULL;

        if (first != NULL)
        {
            temp2=(NODE *)malloc(sizeof(NODE));

            temp2=first;
            while (temp2 != NULL && !found)
            {
                if (temp2->num == newNode->num) 
                {found=true;}

                temp2= temp2->ptr;
            }

            free(temp2);

            if (!found)
            { 
                last->ptr=newNode;
                last=newNode;
                count=count+1;
            }   
        }   
        else  
        {
            first = newNode;
            last = newNode;
            count=count+1;
        }

        fflush(stdin);
    }

Flagstaff

What is the purpose of this program fragment ? BTW: temp2=(NODE *)malloc(sizeof(NODE)); temp2=first; will at least leak memory. – Washbowl

You should check (first->ptr) != NULL – Agony

fflush have undefined behavior. If you want to discard data on stdin, read them and discard but avoid the usage of fflush. – Capreolate

Possible duplicate of How to track down a "double free or corruption" error – Cowbird

Answer 1

The problem is here:

        temp2=first;

Basically, when you free temp2, you free first, not the memory allocated here:

        temp2=(NODE *)malloc(sizeof(NODE));

, which remains a memory leak, because after the assignment it can't be freed anymore.

Also, your code has probably some more problems (one is that you shouldn't use fflush on an input stream), but without some more details, it's impossible to tell.

Calcariferous

@Abhineet: I don't think Paul92 meant to; to me it looks like he just made a typo. He meant to write shouldn't but didn't hit the n. So what came out was should't which you read as should. – Shafer