我根本找不到的C内存泄漏

Question

So everything is fine with the program but i get a very annoying memory leak. I am sitting in front of my computer for couple hours and can figure it out.

We have 2 struck very simple, one struct is a double linked list and one is a hash table that stores that double linked list.

Now i am inserting a key and a data into the double linked list here is the function.

void htable_insert(htable* ht, int key, int data) {
    // TODO: Insert a new entry with the given key and data
    // Overwrite the old data if the key already exists, duplicate keys are not allowed
    ht_entry *new_node;
    ht_entry *head;
    ht_entry *it;
    int sameKey;
    int bucketPosition;

    new_node = (ht_entry*)malloc(1*sizeof(ht_entry));
    bucketPosition = key % ht->size;
    sameKey = 0;

    for(it = ht->entries[bucketPosition]; it != NULL; it = it->next)
    {
      if(it->key == key) {
        it->data = data;
        sameKey = 1;
        free(new_node);
        new_node = NULL;
        break;

      }
    }

    if(!sameKey && new_node) {
      head = ht->entries[bucketPosition];
      if (head == NULL) {
        new_node->key = key;
        new_node->data = data;
        new_node->next = head;
        new_node->prev = NULL;
        ht->entries[bucketPosition] = new_node;
        new_node = NULL;

      } else {
        new_node->key = key;
        new_node->data = data;
        new_node->next = head;
        // new_node->prev = head;
        head->prev = new_node;
        head = new_node;
        ht->entries[bucketPosition] = head;

      }
    }
    // free(new_node);
    new_node = NULL;
    printf("%s\n %d", "INSERT:", key);
    for(it = ht->entries[bucketPosition]; it != NULL; it = it->next){
      printf("it->key: %d\nit->data: %d\n", it->key, it->data);
    }


    printf("%s\n", "-------------------------------");


}

Here is my valgrind message:

==10692== Memcheck, a memory error detector
==10692== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==10692== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==10692== Command: ./chain_hash_table.out
==10692== 
==10692== 
==10692== HEAP SUMMARY:
==10692==     in use at exit: 72 bytes in 3 blocks
==10692==   total heap usage: 10 allocs, 7 frees, 376 bytes allocated
==10692== 
==10692== 24 bytes in 1 blocks are definitely lost in loss record 2 of 3
==10692==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10692==    by 0x4007EE: htable_insert (htable.c:53)
==10692==    by 0x400BD2: main (main.c:14)
==10692== 
==10692== 48 (24 direct, 24 indirect) bytes in 1 blocks are definitely lost in loss record 3 of 3
==10692==    at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==10692==    by 0x4007EE: htable_insert (htable.c:53)
==10692==    by 0x400C25: main (main.c:18)
==10692== 
==10692== LEAK SUMMARY:
==10692==    definitely lost: 48 bytes in 2 blocks
==10692==    indirectly lost: 24 bytes in 1 blocks
==10692==      possibly lost: 0 bytes in 0 blocks
==10692==    still reachable: 0 bytes in 0 blocks
==10692==         suppressed: 0 bytes in 0 blocks
==10692== 
==10692== For counts of detected and suppressed errors, rerun with: -v
==10692== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

And what i know it is always for first table insertion that is why it says at line main(18) for the rest after the first insertion there is no leaks.

Thank you guys for your time and help :)

Answer 1

Check the break statement in the loop, it breaks on the first iteration and it does not deallocate the node.

The break should be placed inside the for loop.

Answer 2

If you are mallocing space in a C program, unless you free everything at the end, you will end up with memory leaks.

For your current program, I'm assuming that you don't free correctly in the end. So the problem isn't within the htable_insert function, but rather within your freeing/cleanup functions.

If you free your linked list nodes in your htable_insert , you will not be able to access them in the rest of your program and you'll run into segfaults.