Question

I have the following code:
(I kept only the relevant part for my question)

        // Structure
        struct first_list {
            char firstname[100];
            struct first_list * next;
        };
        struct last_list {
            char lastname[100];
            struct last_list * next;
        };

        void verify_name()
        {
            char firstname[100];
            char lastname[100];
            struct first_list * curr_first = loaded_first;
            struct last_list * curr_last = loaded_last;

        /////////// this part was added by me
            while( curr_last != NULL )
            {
                strncpy(lastname, curr_last->lastname, sizeof( lastname ) - 1 );
                valid = validate_name(sock,buffer,sizeof(buffer),firstname);
                if(valid < 1)
                    fprintf(stderr, "%s is VALID\n", lastname);
                else
                    fprintf(stderr, "%s is invalid\n", lastname);

                curr_last = curr_last->next; //this is used for removing current record

            }
            printf( "LastName validation complete\n" );
            break;
        /////////// end of part added by me

            while( curr_last != NULL && curr_first != NULL )
            {
                strncpy(firstname, curr_first->firstname, sizeof( firstname ) - 1 );
                strncpy(lastname, curr_last->lastname, sizeof( lastname ) - 1 );

                ////////////////////////////////
                //// irrelevant code (functions)
                ////////////////////////////////

                if( curr_first->next == NULL && curr_last->next != NULL)
                {
                    curr_last = curr_last->next;
                    curr_first = loaded_first;
                }
                else 
                    curr_first = curr_first->next;
            }
        }

so, I added a new function to validate lastnames before the function which validates firstnames and lastnames at the same time (to optimize the whole process). The problem is that if I remove the break command I get an error cause last_list is empty after validation.

How can I keep only the valid last names in the structure because right now when is moving to the next record it is deleting the current one until loop is complete(NULL) ??

Answer 1

What you need to do in your first loop is:

struct last_list * prev = NULL;
struct last_list * next = NULL;
while (curr_last != NULL)
{
  next = curr_last->next;
  strncpy(lastname, curr_last->lastname, sizeof(lastname) - 1);
  lastname[sizeof(lastname) - 1] = 0;
  valid = validate_name(sock,buffer,sizeof(buffer),firstname);
  if(valid < 1)
  {
    fprintf(stderr, "%s is VALID\n", lastname);
    prev = curr_last;
  }
  else
  {
    fprintf(stderr, "%s is invalid\n", lastname);
    if (prev == NULL)
      loaded_last = curr_last->next;  //this is used for removing when current is first record
    else
      prev->next = curr_last->next; //this is used for removing current record from mid-list
    free(curr_last); //Freeing should be needed but depends on how you built your list.
  }
  curr_last = next;
}
curr_last = loaded_last;

This will remove your curr_last element from the list and retain only valid lastnames in it.