Infinite while loop in linked list C

Question

I ran into a problem, I want to add item to the end of the linked list, but it seems that i am getting sucked in an infinite loop here.

void addCheckPoint(struct checkPoints **checkPoint) {
    struct checkPoints *checkPt = *checkPoint;

    while (checkPt->next != NULL) {
        checkPt->next;
        if (checkPt->next == NULL) {
            scanf("%c %d %d %d %d", &checkPt->dropOut, &checkPt->currentPoint, &checkPt->competitor, &checkPt->hour, &checkPt->minute);
        }
    }
}

http://stackoverflow.com/questions/13875395/linked-list-head-address-changes-c — anishsane, Dec 14 '12 at 10:49
Possible duplicate of [What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — Raedwald, Oct 06 '18 at 08:28

score 3 · Answer 1 · answered Dec 14 '12 at 09:56

You never update the value of checkPt in your loop. Change the line

checkPt->next;

to

checkPt = checkPt->next;

to fix this.

Note that there may be further problems with the function. Despite its name, it doesn't actually add anything to the list. It edits the contents of the tail item instead. If this isn't deliberate, you'll need to malloc a new element then add it to the tail.

score 2 · Accepted Answer · answered Dec 14 '12 at 09:57

void addCheckPoint(struct checkPoints **checkPoint) {
    struct checkPoints *checkPt = *checkPoint;

    while (checkPt != NULL) {
        if (checkPt->next == NULL) {
            scanf("%c %d %d %d %d", checkPt->dropOut, checkPt->currentPoint, checkPt->competitor, checkPt->hour, checkPt->minute);
        }
        checkPt = checkPt->next;
    }
}

score 1 · Answer 3 · answered Dec 14 '12 at 09:58

1

try this

 void addCheckPoint(struct checkPoints **checkPoint) {
        struct checkPoints *checkPt = *checkPoint;

        while (checkPt->next != NULL) {
             checkPt=checkPt->next;
            if (checkPt == NULL) {
                scanf("%c %d %d %d %d", &checkPt->dropOut, &checkPt->currentPoint, &checkPt->competitor, &checkPt->hour, &checkPt->minute);
            }

        }
    }

answered Dec 14 '12 at 09:58

Charan Pai

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Suppose there are 0 nodes in the linked list, so `*checkPoint` will be NULL in that case..and `(*checkPoint)->next` will cause error. – Adeel Ahmed Dec 14 '12 at 10:05
he might be sending a root node.. i don no his aim der – Charan Pai Dec 14 '12 at 10:08

score 0 · Answer 4 · answered Dec 14 '12 at 10:22

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

struct checkPoints
{
    char dropOut;
    int currentPoint;
    int competitor;
    int hour;
    int minute;

  struct checkPoints *next;
};

void addCheckPoint(struct checkPoints **checkPoint) {
    while (*checkPoint)
        checkPoint = &(*checkPoint)->next;

    /* FIXME: check malloc() return value */
    *checkPoint = malloc(sizeof (struct checkPoints));
    (*checkPoint)->next = 0;

    /* NOTE: the leading space in front of the %c */
    scanf(" %c %d %d %d %d",
          &(*checkPoint)->dropOut,
          &(*checkPoint)->currentPoint,
          &(*checkPoint)->competitor,
          &(*checkPoint)->hour,
          &(*checkPoint)->minute);
}

struct checkPoints *list = 0;

int
main ()
{
    addCheckPoint (&list);
    addCheckPoint (&list);
}

Infinite while loop in linked list C

4 Answers4