to delete the element of the linked list by using memcmp

Question

In this code i want to delete any element in the list this is being done by delpos, i am using memcmp to do it, i am doing this as i have to use this same logic in another program where i get a value and i have to compare that value present in the linked list,(there i wll be comparing structure so strating off with just an integer) can any one please tell what mistake i have done in delpos, while displaying it is displaying some junk values.

#include<stdio.h>
#include<stdlib.h>

void insertbeg();
void delpos();
void display();

struct node {
    int info;
    struct node *link;
} *first = NULL;

struct node *create();
int item, key;

main() {
    int choice;
    while (1) {
        printf("\nchoices are:\n");
        printf("\n1.Insertbeg\n2.delpos\n3.display\n4.exit\n");
        printf("Enter U'r choice: ");
        scanf("%d", &choice);
        switch (choice) {
            case 1: insertbeg();
                break;
            case 2: delpos();
                break;
            case 3: display();
                break;
            case 4: exit(1);
            default: printf("INVALID CHOICE TRY AGAIN\n");

        }
    }
}

struct node *create() {
    struct node *new;
    new = (struct node*) malloc(sizeof (struct node));
    return (new);
}

void insertbeg() {
    struct node *new;
    new = create();
    printf("Enter element to be inserted: ");
    scanf("%d", &item);
    if (first == NULL) {
        new->info = item;
        new->link = NULL;
        first = new;
    } else {
        new->info = item;
        new->link = first;
        first = new;
    }
}

void delpos() {
    int key;
    struct node *temp, *prev = NULL;
    int cmp_value, cmp_value1;
    if (first == NULL) {
        printf("LIST IS EMPTY\n");
        return;
    } else {
        temp = first;
        printf("Enter the KEY element which is to be deleted: ");
        scanf("%d", &key);
        while (temp->link != NULL) {
            cmp_value = memcmp(&temp->info, &key, 4);
            if (cmp_value == 0) {
                if (prev == NULL)
                    first = temp->link;
                else
                    prev->link = temp->link;
            }
            else {
                prev = temp;
                cmp_value1 = memcmp(&temp->info, &key, 4);
                temp = temp->link;
                free(temp);
            }            
        }
    }
}

Dont use 4 but sizeof(int), as the size of an int isn't guarranted to be 4bytes... See Alex B response in this post: http://stackoverflow.com/questions/589575/c-size-of-int-long-etc — roirodriguez, May 06 '11 at 07:54
You seem to have pasted the last else block twice... I'm editing it, edit it back if i'm wrong — roirodriguez, May 06 '11 at 07:59

score 1 · Accepted Answer · answered May 06 '11 at 07:56

It seems that your delete condition is not in the right way :

     cmp_value = memcmp(&temp->info, &key, sizeof(int)); // sizeof(int) is better than 4
     if (cmp_value == 0)            // here, the items are the same, so you should delete it
     {
        if (prev == NULL)
           first = temp->link;
        else
           prev->link = temp->link;
           // I think you missed a free(temp); here
     }else                          // here, the items are different
     {
        prev = temp;
        cmp_value1 = memcmp(&temp->info, &key, 4);    // why are you comparing again items ??
        temp = temp->link;
        free(temp);                       // why are you freeing the item ?
     }
     // you have to change the value of your temp pointer at the end of the while loop, otherwise, you are not going to correctly check all the items.

to delete the element of the linked list by using memcmp

1 Answers1