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Segmentation fault in fopen when in write mode.

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Top Forums Programming Segmentation fault in fopen when in write mode.
# 8  
Old 07-17-2012
In what way does it fail to execute, though?
# 9  
Old 07-17-2012
The same old segmentation fault message:

Code:
Program received signal SIGSEGV, Segmentation fault.
0x00000031f4a7873e in _int_malloc () from /lib64/libc.so.6

# 10  
Old 07-17-2012
Unless I missed something, all of the following code can be replaced with two snprintf (or sprintf) calls. (It probably has nothing to do with your segfault, but needless complexity never helps.)

Quote:
Originally Posted by shoaibjameel123
Code:
void file_names ( unsigned int i , char * file_name , char * str )
{
    char common_path[] = {"/data/scores/"};

    str = itoa ( i  , str );
    strcat ( file_name , common_path );
    strcat ( str , ".dat" );
    strcat ( file_name , str );
}


void file_name_generator ( unsigned long int i , char * file_name , char *str )
{
    strcat ( file_name , "/data/files/" );
    str = itoa ( i , str );
    strcat ( file_name, str );
    strcat ( file_name , ".dat" );
}


char * itoa ( int n , char * s )
{
     int i, sign;
 
     if ( ( sign = n ) < 0 )  /* record sign */
         n = -n;          /* make n positive */
     i = 0;
     do {       /* generate digits in reverse order */
         s [ i++ ] = n % 10 + '0';   /* get next digit */
     } while ( ( n /= 10 ) > 0 );     /* delete it */
     if ( sign < 0 )
         s [ i++ ] = '-';
     s [ i ] = '\0';
     reverse ( s );
    return ( s );
}


char * reverse ( char s [ ] )
{
     int i, j;
     char c;
 
    for ( i = 0, j = strlen ( s ) - 1; i < j; i ++, j -- ) 
    {
             c = s [ i ];
             s [ i ] = s [ j ];
             s [ j ] = c;
         }
    return ( s );
}

Regards,
Alister

---------- Post updated at 12:26 AM ---------- Previous update was at 12:10 AM ----------

I haven't tried to compile your code, just looking it over, but the following is wrong:
Code:
str = ( char * ) malloc ( 4 * sizeof ( char ) );

void file_names ( unsigned int i , char * file_name , char * str )
{
    char common_path[] = {"/data/scores/"};

    str = itoa ( i  , str );
    strcat ( file_name , common_path );
    strcat ( str , ".dat" );
    strcat ( file_name , str );
}

str doesn't even have enough room for ".dat", which requires 5 bytes.

Regards,
Alister
Last edited by alister; 07-17-2012 at 01:38 AM..
# 11  
Old 07-17-2012
Great solved the problem:

This is what I did. Put this piece of code
Code:
fclose ( input_file );

Like this:
Code:
        while ( !feof ( input_file ) )
        {
            while ( ( read = getline ( &line , &len , input_file ) ) != -1 )
            {
                line = chomp ( line );
                strcpy ( words_from_webpage [ j ] , line );
                if ( j <= number_of_words )
                {
                    j ++;
                }
            }
        }
        
        fclose ( input_file );

And BINGO!!! it worked Smilie

Also, thanks Alister, yes that was my mistake. I have increased the size of str. But there now I have encountered another problem.

When the following section comes:

Code:
while ( j < number_of_words )
        {
            fprintf ( output_pointer , "%ld\n" , store_values [ j ]);
            j ++;
        }
fclose ( output_pointer );

The program now faults again.
Code:
*** glibc detected *** /data/compute_scores.out: free(): corrupted unsorted chunks: 0x000000001d6ed3b0 ***

Program received signal SIGSEGV, Segmentation fault.
0x00000031f4a7873e in _int_malloc () from /lib64/libc.so.6

This happens when I go to the next line after
Code:
fclose ( output_pointer );

in gdb

---------- Post updated at 12:42 PM ---------- Previous update was at 12:39 PM ----------

Now the problem does not occur with
Code:
output_pointer = fopen ( file_name , "w" );

but with
Code:
fclose ( output_pointer );

---------- Post updated at 02:43 PM ---------- Previous update was at 12:42 PM ----------

Finally the problem has been solved and the program is executing perfectly. I have made one change in the program.

Take out all malloc() calls inside this for loop and initialize them outside the loop.
Code:
for ( i = 0 ; i < NUMBER_OF_FILES ; i ++ )

After placing the following statements outside, the code runs well.

Code:
store_values = ( unsigned long int * ) malloc ( number_of_words * sizeof ( unsigned long int ) ); this array will store all the numerical values corresponding to the words
        if ( store_values == NULL )
        {
            fprintf ( stderr , "malloc() memory allocation failure\n" );
        }

        words_from_webpage = ( char ** ) malloc ( number_of_words * sizeof ( char * ) ); //this read the data file consising of words each word in newline
        if ( words_from_webpage == NULL )
        {
            fprintf ( stderr , "malloc() memory allocation failure in words_from_webpage\n" );
        }

        for ( j = 0 ; j < number_of_words ; j ++ )
        {
            words_from_webpage [ j ] = ( char * ) malloc ( 20 * sizeof ( char ) );
            if ( words_from_webpage [ j ] == NULL )
            {
                fprintf ( stderr , "malloc() memory allocation failure\n" );
            }
        }

But now I have to pre-define the value of
Code:
number_of_words

. SO, I used #define preprocessor declaration and hard coded this value.

I am not sure why allocation of memory inside the for loop did not work.
# 12  
Old 07-17-2012
That loop is leaking memory badly. Each time store_values and words_from_webpage are assigned a pointer, the only references to the un-free()'d memory allocated during the previous iteration are lost.

Perhaps there are other problems, but I just focused on what you highlighted in your most recent post.

Why are you using C for this? A learning exercise? If so, great. If not, consider using awk, perl, python, or something else that operates at a higher level. You're not gaining much by using C for this and you are wasting a lot of time with the memory management bugs. If it must be C, you'll probably benefit from using static analysis tools (valgrind, for example).

Also, consider that there's no reason (other than educational) to bother with itoa(), reverse(), and the string generating functions that they are supporting. snprintf() will do everything that they are doing.

Regards,
Alister
Last edited by alister; 07-17-2012 at 11:38 AM..
This User Gave Thanks to alister For This Post:
shoaibjameel123
# 13  
Old 07-17-2012
Yes, in the loop things were not perfect and memory leak was excessive. I've fixed some of the other problems too, but those are minor.

There are some reasons why I use C for everything. One is that I work on extremely large sets of text files and do mathematical computations using those files. Hence, efficiency is one reason. But indeed I do have to toil extra hard to get my code perfect.

snprintf() is a valid suggestion and can get my code a lot more compact and readable. Thanks for that. I'll use it in my future codes.

One big reason why I stick to C is "passion". Just like some people love climbing Mount Everest but others think that they are wasting their precious time and life. (The last sentence is just a joke Smilie).
# 14  
Old 07-17-2012
Quote:
Originally Posted by shoaibjameel123
One big reason why I stick to C is "passion".
Understood. Smilie

Regards,
Alister
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