listnode循环，分段错误

Question

Haven't managed to find a simplified version of this problem.

I'm new to listnodes so I probably just don't understand something simplea bout them. Everything seems to work until I pass my for loop.

while(temp2 != NULL){

    for(int i = temp2->data; i > 0; i--){
    //////////////
    temp1 = head;
    temp3 = Product.head;

        while(temp1 != NULL || temp3 != NULL){
            cout << "\ntemp1->data: " << temp1->data;
            cout << "\ntemp3->data: " << temp3->data;


            temp1 = temp1->next;
            temp3 = temp3->next;
        }
    /////////////
    cout << "\n\ndecrement: " << i;
    }

temp2 = temp2->next;    
}

Everything runs except between the comments.

My thought was that I could traverse to the end of the listnode (temp1), then once I reached the end I point back to the head and traverse through it as many times as necessary. I'm getting a segmentation fault there though.

I cant traverse through temp2 just fine, what am I doing wrong though when it comes to traversing through temp1 multiple times? Can I only refer to the head of the list once?

edit: I figured out that I just left a conditional in. Now Its my 3rd list that is giving me the segmentation fault. it will run for a single loop but once out of the while loop it breaks.

Answer 1

Think about it like this. In a specific iteration of your while loop, temp1 points to an address and temp1->next points to NULL . temp3 points to an address and temp3->next also points to an address.

temp1 == address

temp1->next == NULL

temp3 == address

temp3->next == NULL

You iterate through the current address, printing the data from temp1 and temp3 . Then you set them equal to their next pointers. Now temp1 points to NULL and temp3 points to an address.

Your condition of the while loop checks to see if either of the pointers do not point to NULL . Because temp3 does not point to NULL , it will try to print out the data for temp1 and temp3 . But this will cause a problem because temp1 points to NULL and you are trying to dereference a NULL pointer, which will cause a segmentation fault.

To solve this issue, you should use an AND (&&) condition for your while loop so that it only prints when temp1 AND temp3 don't point to NULL .