Qsort not sorting char * array

Question

I've got a problem, which is, qsort sometimes sorts stuff, sometimes it doesn't. Here's my code

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


static int compare (const void * a, const void * b)
{
  return strcmp (*(const char **) a, *(const char **) b);
}

int main (){
  int ile = 0;
  scanf("%d", &ile);
  const char * slowa[ile];
  for(int j = 0; j <= ile; j++){
    char string[30];
    gets(string); 
    char * toAdd = strdup(string);
    slowa[j] = toAdd;
  }
  qsort (slowa, ile, sizeof (const char *), compare);

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

It works well with example { ccc,bbb,aaa } but does not work for the example { afdg ,sspade , trekk, bbre, lol}

You iterate once too many, should be j < ile; and i < ile; — Weather Vane
– Weather Vane, Commented Dec 5, 2016 at 10:18

Weather Vane · Accepted Answer · 2016-12-05 10:36:26Z

2

The scanf has left a newline in the input buffer, which is read by the first gets.

The two loops iterate once too many, indexing the array beyond its bounds. I guess you did that to get the correct number of apparent inputs.

So clear the input before the first loop, perhaps with a dummy string read, and correct the loop control.

Also please note that gets() is now obsolete.

answered Dec 5, 2016 at 10:36

Weather Vane

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2 Comments

Karol.T Over a year ago

i've add fflush(stdin) and corrected the loop control, works perfectly. Thanks

Weather Vane Over a year ago

@Karol.T please note that fflush(stdin) is non-standard behaviour.

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