Question

I am trying to implement a binary search tree by reading lines from a file.

  while(fgets(p, 1024, fp))
  {
     struct node child;
     child.str = (char *)malloc(plen);      
     strcpy(child.str,p);
     insert(&tree,&child);
  }

Now the problem is that I can not seem to find a way to make a complete new copy of child, instead it just changes its values every time the while loop restarts.

Answer 1

That’s because the pointer-to-child (&child) isn’t changing. You can convince yourself of this by printing it out:

printf("address of child = %p\n", &child);

Solution: You also need to allocate the node as well:

struct node*child = malloc(sizeof(struct node));

You can then assign child.str as you were, now using pointer-syntax:

child->str = (char *)malloc(plen);      
strcpy(child->str,p);

…and because the child is a pointer, you don’t need the ampersand here:

insert(&tree,child);