segmetation fault (reading and writing file in c)

Hi all;

I have problem in C. the problem is ,Here is my code

Code:

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


/*  uni() function takes an array an thier size.and it produce an array which is include unique element  */
int uni(char **arr,int size)
{
  int unique = 0; /* The length of dst after removing duplicates */
  int n=size;
  char *dst[n];     /* The set of stirings without duplicates */
  int i;

  /* The first number is never a duplicate */
  dst[unique++] = arr[0];

  /* Load the unique strings into the destination list */
  for ( i = unique; i < n; i++ ) {
    int has_dup = 0;
    int j;

    for ( j = 0; j < unique; j++ ) {
      if ( arr[i] == dst[j] )
        has_dup = 1;
    }

    if ( has_dup == 0 )
      dst[unique++] = arr[i];
  }

 /* Display the unique strings*/
   for ( i = 0; i < unique; i++ )
    printf ( "%s ", dst[i] );
  printf ( "\n" );

  return 0;
}

int main ( void )
{
   static const char filename[] = "input1.txt";    
   char colour[20],name[20];
   char *image[1000];

   int i=0,h,x,y,w;
   FILE *file = fopen ( filename, "r" );
   if ( file != NULL )
   {
      char line [ 128 ]; /* or other suitable maximum line size */

      while ( fgets ( line, sizeof line, file ) != NULL ) /* read a line */
      {         
	sscanf(line,"%s%d%d%d%d%s",name,&w,&h,&x,&y,colour); 

               image[i]=colour;
               i++;
      }
      uni(image,1000);
	
      fclose ( file );
   }
   else
   {
      perror ( filename ); /* why didn't the file open? */
   }
   return 0;
}

input1.txt file include 1000 line something like that:

Code:

rectangle 0 0 1 1  orange
rectangle 0 1 1 1  green
rectangle 0 2 1 1  white
rectangle 0 3 1 1  orange
rectangle 0 4 1 1  white
rectangle 0 5 1 1  black
rectangle 0 6 1 1  blue
rectangle 0 7 1 1  red
rectangle 0 8 1 1  blue
rectangle 0 9 1 1  white
rectangle 0 10 1 1  green
rectangle 0 11 1 1  green
rectangle 0 12 1 1  orange
rectangle 0 13 1 1  red
rectangle 0 14 1 1  white
rectangle 0 15 1 1  green
rectangle 0 16 1 1  red
rectangle 0 17 1 1  black

i have read the input1.txt file then
i want to take only colour word.then
i want the hold this colour in array then
i want to sent this array uni funcion then
finally i want to print this array stdout.

I want to do all of this steps , but my programs give me segmentation fault. !can i anyone help me?

First error:

Code:

               image[i]=colour;

is probably not what you want to do. You are copying the address of colour into image[i]. Since the next sscanf() will overwrite the content of colour, all you ever will get is the last colour FOR ALL of your image[0..n] entries.

Second:

Code:

      if ( arr[i] == dst[j] )
        has_dup = 1;

Again, you are using the address of a string to compare with another. If you were to fix the above problem, this would fail for every string [as the code stands now, every string is a duplicate, since all strings are set to the same address]. You need to use strcmp() to compare strings - and notice that strcmp returns 0 for a match.

This does in fact work, as long as you do not need dst AFTER the image variable is gone.

Code:

    if ( has_dup == 0 )
      dst[unique++] = arr[i];

--
Mats

Originally Posted by tasosa

Hi all;

I have problem in C. the problem is ,Here is my code

Code:

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


/*  uni() function takes an array an thier size.and it produce an array which is include unique element  */
int uni(char **arr,int size)
{
  int unique = 0; /* The length of dst after removing duplicates */
  int n=size;
  char *dst[n];     /* The set of stirings without duplicates */
  int i;

  /* The first number is never a duplicate */
  dst[unique++] = arr[0];

  /* Load the unique strings into the destination list */
  for ( i = unique; i < n; i++ ) {
    int has_dup = 0;
    int j;

    for ( j = 0; j < unique; j++ ) {
      if ( arr[i] == dst[j] )
        has_dup = 1;
    }

    if ( has_dup == 0 )
      dst[unique++] = arr[i];
  }

 /* Display the unique strings*/
   for ( i = 0; i < unique; i++ )
    printf ( "%s ", dst[i] );
  printf ( "\n" );

  return 0;
}

int main ( void )
{
   static const char filename[] = "input1.txt";    
   char colour[20],name[20];
   char *image[1000];

   int i=0,h,x,y,w;
   FILE *file = fopen ( filename, "r" );
   if ( file != NULL )
   {
      char line [ 128 ]; /* or other suitable maximum line size */

      while ( fgets ( line, sizeof line, file ) != NULL ) /* read a line */
      {         
	sscanf(line,"%s%d%d%d%d%s",name,&w,&h,&x,&y,colour); 

               image[i]=colour;
               i++;
      }
      uni(image,1000);
	
      fclose ( file );
   }
   else
   {
      perror ( filename ); /* why didn't the file open? */
   }
   return 0;
}

input1.txt file include 1000 line something like that:

Code:

rectangle 0 0 1 1  orange
rectangle 0 1 1 1  green
rectangle 0 2 1 1  white
rectangle 0 3 1 1  orange
rectangle 0 4 1 1  white
rectangle 0 5 1 1  black
rectangle 0 6 1 1  blue
rectangle 0 7 1 1  red
rectangle 0 8 1 1  blue
rectangle 0 9 1 1  white
rectangle 0 10 1 1  green
rectangle 0 11 1 1  green
rectangle 0 12 1 1  orange
rectangle 0 13 1 1  red
rectangle 0 14 1 1  white
rectangle 0 15 1 1  green
rectangle 0 16 1 1  red
rectangle 0 17 1 1  black

i have read the input1.txt file then
i want to take only colour word.then
i want the hold this colour in array then
i want to sent this array uni funcion then
finally i want to print this array stdout.

I want to do all of this steps , but my programs give me segmentation fault. !can i anyone help me?

I think problem is char *dst[n]; with statement.
It requires constant expression same as switch statment.

Originally Posted by shwetha_siddu

I think problem is char *dst[n]; with statement.
It requires constant expression same as switch statment.

The compiler would complain if that was the case (and there is of course nothing to prevent a const being added to size [and n is really not needed!] - but compilers know if something is a constant or not, and should give an error, not cause a seg-fault.

--
Mats

1. why are you passing 1000 as array size if only i strings were entered?
2. image[i]=colour; - you just store pointer to the local buffer, this pointer will be the same on each iteration, and buffer will be overwritten with the new data on the next iteration
3. arr[i] == dst[j] - this compares pointers not strings, to compare strings strcmp function should be used
4. has_dup = 1;
you can exit the loop after that - no need to continue checking other strings

Originally Posted by matsp

First error:

Code:

               image[i]=colour;

is probably not what you want to do. You are copying the address of colour into image[i]. Since the next sscanf() will overwrite the content of colour, all you ever will get is the last colour FOR ALL of your image[0..n] entries.

--
Mats

actually i think main problem is that. When i compile the program it produce only one colour like you say "last colour FOR ALL of your image[0..n] entries. ". how can i manage. what should i do in order to fix this problem. i want to store colour into the array