使用链接列表结构跟踪C程序中可能的内存泄漏

Question

This program is supposed to read inputs until 0 or a negative number is read. Then put it into a linked list in ascending order using the structure below.

When I was emailed the test cases 0-3 I passed them all. Those inputs consist of numbers that are random such as 1 2 3 4 5 -1 or 3493494 2922 -1.

The last input file which is "#### failed test" consists of a blank page which is the input txt. So my program automatically says "The linked list is empty". However there is a memory check error.

Is this error because of the block? Should "free(curr);" be after the printf?

  if(head == NULL)
  {
     printf("The list is empty\n");
     return(-1);
  }

I am asking this because when the program runs normally and executes it reaches the last line which free's the memory for the curr variable. But when the list is empty it instantly goes to the "head == NULL" statement and exits without freeing the variable.

My Professor emailed me the test cases where the input is different for each:

 #### Passed test 0.
 #### Passed test 1.
 #### Passed test 2.
 #### Passed test 3.
 #### Failed test MemoryCheck. Output of memory checker follows.
 ==23571== 128 (32 direct, 96 indirect) bytes in 2 blocks are definitely        
 lost in loss record 2 of 2
 ==23571== at 0x4A07218: malloc (vg_replace_malloc.c:296)
 ==23571== by 0x40071A: main (in /eecs/dept/course/2015-    
 16/F/2031/submit/lab7/cse13020/q2) 
 ==23571== 

Code:

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


struct node
{
   int node;
   struct node* next;
};


void insert(struct node** head, struct node* node)
{
    struct node* curr;

    if (*head == NULL || (*head)->node >= node->node)
    {
       node->next = *head;
       *head = node;
    }
    else
    {
       curr = *head;

        while (curr->next!= NULL && curr->next->node < node->node)
           curr = curr->next;

        node->next = curr->next;
        curr->next = node;
    }
}


int main()
{

   struct node *head = NULL;
   struct node *curr;

   int n;

   while(1)
   {

      scanf("%d", &n);

      if(n <= 0) 
        break;

      curr = (struct node*) malloc(sizeof(struct node));
      curr->node  = n;
      curr->next =  NULL;

      insert(&head, curr); 
   }

  if(head == NULL)
  {
     printf("The list is empty\n");
     return(-1);
  }

  printf("The linked list is:\n");

  while(1)
  {
     if(head == NULL) {
       printf("NULL\n");
       break;
     }
     printf("%d-->", head->node);
     head = head->next;
  }


  free(curr);  
}

Answer 1

you need to free the head node in the last while loop:

while(1)
{
  if(head == NULL) {
    printf("NULL\n");
    break;
  }
  printf("%d-->", head->node);
  void *tmp = head;
  head = head->next;
  free(tmp);
}

and remove the free(curr); .

You should also check scanf for success or set n to some negative value before.