CODEWITHSUNDEEP
c
Tripswitch
Tripswitch

Reputation: 13

Removing duplicate strings

I need help in removing duplicate strings. My code is almost there, it outputs the unique strings then crashes, see for yourself. How can I stop this from happening?

#include <stdio.h>
#include <string.h>

int main(void) 
{
    char array[4][4]={"cat","mat","sat","mat"};
    int i, j, k;
    int a=4;

   for (i = 0;i < a; i++) 
   {
      for (j = i + 1; j < 4;) 
      {
         if (strcmp(array[j],array[i])==0)
         {
            for (k = j; k < a; k++) 
            {
               strcpy(array[k],array[k+1]);
            }

            a--;
         } 

         else
         j++;
      }
   }

   for (i = 0; i < a; i++) 
   {
      printf("%s", array[i]);
   }

   return (0);
}

Upvotes: 0

Views: 94

Answers (3)

Vlad from Moscow
Vlad from Moscow

Reputation: 311018

Your approach is not good. When you find a matched string you copy all tail of the array in the new position.

Here is a more simple and clear approach

#include <stdio.h>
#include <string.h>

#define N   4

int main(void) 
{
    char s[N][N] = { "cat", "mat", "sat", "mat" };
    int i, j;

    j = 0; /* current osition where a unique string will be placed */
    for ( i = 0; i < N; i++ ) 
    {
        int k = 0;
        while ( k < j && strcmp( s[k], s[i] ) != 0 ) k++;

        if ( k == j )
        {
            if ( j != i ) strcpy( s[j], s[i] );
            j++;
        }
    }


    for ( i = 0; i < j; i++ ) printf( "%s ", s[i] );
    puts( "" );

    return 0;
}

The output is

cat mat sat

Simply copy paste and investigate.:)

Upvotes: 1

Rafał Augustyniak
Rafał Augustyniak

Reputation: 2031

It is better to use strncmp that strcmp. You don't have to iterate through every character of the string as strncmp compares strings tills the their end (null terminated strings). From the documentation (man strncmp on unix systems) of the strncmp:

The strncmp() function compares not more than n characters. Because strncmp() is designed for comparing strings rather than binary data, characters that appear after a `\0' character are not compared.

Try this code:

char array[4][4]={"cat","mat","sat","mat"};
int i, j;
int a = 4;

 for (int i = 0; i < a; i++) {

    bool unique = true;
    for (int j = i + 1; j < a; j++) {
       if (strncmp(array[i], array[j], a) == 0) {
          unique = false;
          break;
       }
    }

    if (unique) {
      printf("%s\n", array[i]);
    }
 }

Upvotes: 0

Fiddling Bits
Fiddling Bits

Reputation: 8861

If you stepped through your program with a debugger you'd find out that the following is your problem:

strcpy(array[k],array[k+1]);

When k == 3 you're attempting to access an element outside the bounds of array for the second argument of strcpy:

array[k+1]

Upvotes: 2

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