CODEWITHSUNDEEP
arrayscstringpointers
michael368
michael368

Reputation: 43

How to remove the duplicate strings from an array of strings in c

I am trying to make program where I have a linked list that has different names of cities + some other irrelevant stuff. City names are, for ex. "Seattle, Boston, New York, Seattle, Washington, Boston". What I am trying to do is make an array that only has unique names of the cities. So for given example, it would be this: "Seattle, Boston, New York, Washington".

My idea was to make a raw array of strings, which would be just the raw data with all the duplicates and then go through each city and make all the other appearances of them "NULL". For some reason, it does not work properly, I have no idea why.

Also, I would appreciate if you guys could help me with your own, easier versions of the solution.

Here is my code:

void city_list(City *head)
{
    City *temp = head;

    char** names_raw;
    char** names_new;
    int num_names = 100;
    int curr_pos = 0;

    names_raw = malloc(num_names * sizeof(char*));

    for(int i = 0; i < num_names; i++)
    {
        names_raw[i] = malloc(256 * sizeof(char));
    }

    while(temp != NULL)
    {
       
        strcpy(names_raw[curr_pos++], temp->name);

        temp = temp->next;
    }

    names_new = malloc(num_names * sizeof(char*));

    for(int i = 0; i < num_names; i++)
    {
        names_new[i] = malloc(256 * sizeof(char));
    }

    for(int i = 0; i < curr_pos; i++)
    {
        if(strcmp(names_raw[i], "NULL"))
        {
            for(int j = i+1; j < curr_pos; j++)
            {
                if(!strcmp(names_raw[j], names_new[i]))
                {
                    strcpy(names_raw[j], "NULL");
                }
            } 

            strcpy(names_new[i], names_raw[i]);
        }
    }

    for(int i = 0; i < curr_pos; i++)
    {
        printf("%s\n", names_new[i]);
    }

    free(names_raw);
    free(names_new);
}

When I debug the code, I don't get any errors, but it prints out all the cities, like nothing was done with the array.

Upvotes: 3

Views: 729

Answers (1)

paulsm4
paulsm4

Reputation: 121669

You've not shown us a complete example (What is "City"? How is your input array built? Etc etc). But I suspect you're making things over-complicated :(

SUGGESTION:

  1. Pass your array into a function named int delete_dupes(char* arr[], int n) (or similar)

  2. Sort the array:

    EXAMPLE CODE: https://www.geeksforgeeks.org/c-program-sort-array-names-strings/

  3. "Delete" the duplicates by moving them to the front of your array

    int delete_dupes(char* arr[], int n) {
  char *current_name = arr[0];
  int i=1, j=1;
  while (i < n) {
    if (strcmp(arr[i], current_name) != 0) {
      free(arr[j]);  /* Do *NOT* do this if you didn't malloc() this string!!!! */
      arr[j++] = arr[i];
      current_name = array[i];
    }
  }
  return j;
}

  4. The function returns the new #/strings. That number will be <= n.

    Additionally, you may want to null out the unused array elements and/or free the duplicate string values.

  5. An "ideal" solution would be for you to implement a dynamic list.

  6. If you want to "malloc()" each string individually, please consider the standard C library function strdup() .

And no, I haven't tested :)

Upvotes: 0

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