[rishi123]

Below is the program for sorting the file in ascending and reverse order
this program is working properly under window but it gives segmentation fault under unix
Can u find where i m mistaking....
u can give command line arguments like this

./myprogram -a filename.txt for sortin filename in ascending order
./myprogram -r filename.txt for sorting filename in reverse order

Program

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFER_LEN 100  /* Length of input buffer    */
#define NUM_P 100       /* maximum number of strings */
#define TRUE  1
#define FALSE 0

void main(int argc, char *argv[])
{
   FILE *fp;
   char buffer[BUFFER_LEN];    /* space to store an input string    */
   char *pS[NUM_P] = { NULL }; /* Array of string pointers          */
   char *pTemp = NULL;         /* Temporary pointer                 */
   int i = 0, a=0;             /* Loop counter                      */
   int sorted = FALSE;         /* Indicated when strings are sorted */
   int last_string = 0;        /* Index of last string entered      */
   
   if(strcmp(argv[1],"-a")==0)
   a=1;
   if(strcmp(argv[1],"-r")==0)
   a=2;

   fp =fopen(argv[2],"r"); /* Opening the file in read mode     */

   while((*fgets(buffer,(BUFFER_LEN-1),fp) != '\0') && (i < NUM_P))
   {
     pS[i] = (char*)malloc(strlen(buffer) + 1);
     if(pS[i]==NULL)           /* Check for no memory allocated     */
     {
       printf(" Memory allocation failed. Program terminated.\n");
       return;
     }
     strcpy(pS[i++], buffer);
   }
   last_string = i;            /* Save last string index            */

   switch(a)
   {
   case 1:
    {
     /* Sorting in ascending order */
      while(!sorted)
      {
	sorted = TRUE;
	for (i = 0 ; i < last_string - 1 ; i++)
	  if(strcmp(pS[i], pS[i + 1]) > 0)
	  {
	    sorted = FALSE;     /* We were out of order */
	    pTemp = pS[i];      /* Swap pointers pS[i]  */
	    pS[i] = pS[i + 1];  /*       and            */
	    pS[i + 1] = pTemp;  /*     pS[i + 1]        */
	  }
      }
      break;
    }
   case 2:
    {
     /* Sorting in decending order */
      while(!sorted)
      {
	sorted = TRUE;
	for (i = 0 ; i < last_string - 1 ; i++)
	  if (strcmp(pS[i], pS[i + 1]) < 0)
	  {
	    sorted = FALSE;     /* We were out of order */
	    pTemp = pS[i];      /* Swap pointers pS[i]  */
	    pS[i] = pS[i + 1];  /*       and            */
	    pS[i + 1] = pTemp;  /*     pS[i + 1]        */
	  }
      }
      break;
    }
   default:
    {
     printf("wrong argument passed");
     exit(1);
    }
   }
   /* Displayed the sorted strings */
   printf("\nYour input sorted in order is:\n\n");
   for (i = 0 ; i < last_string ; i++)
   {
     printf("%s\n", pS[i] );
     free( pS[i] );
     pS[i] = NULL;
   }
}

[SpOonWiZaRd]

This is the Introduce yourself section....

[shabbir]

Moved to C-C++ forum.

[Salem]

1. main returns int, not void

2. (*fgets(buffer,(BUFFER_LEN-1),fp) != '\0')
When fgets() reaches the end, it returns NULL.
Then when you try to dereference that result, you segfault.
The correct loop condition is
fgets(buffer,(BUFFER_LEN-1),fp) != NULL

Also, you don't have to account for the \0 in your count, so you can just do
fgets(buffer,BUFFER_LEN,fp) != NULL