segmentation fault(core dumped) error while reading array from a input file

Question

I am trying to read an array through input file in C. I am getting segmentation fault(core dumped) error after displaying array. Can anyone please solve this issue. Here is my c program

#include <stdio.h>
#include<stdlib.h>
int main()
{
    int c, i, j, row, col, nl, cr,nt;
     col = nl = cr = nt=0;
    int k;
    row=1;
    FILE *fp = fopen("IO.txt", "r");
    // Figure out how many rows and columns the text file has
   while ((c = getc(fp)) != EOF)
    {
        if (c == '\n')
            nl++;
        if (c == '\r')
            cr++;
        if(c=='\t')
            nt++;
        col++;
        if (c == '\n')
            row++;
        putchar(c);
    }
    //row=row+1;
col = (col - (nl + cr+nt));
col = (int) (col/row); 
char **array = malloc(sizeof(char *) * row);

for(int k=0;k<row;k++) 
{
    array[c] = malloc(sizeof(char) * col);
}

if(fp)
{
    for( ;; )
    {
        c = getc(fp);
        if ( c == EOF )
        {
            break;
        }
        if ( c != '\n' && c != '\r' )
        {
            array[i][j] = c;
            if ( ++j >= col )
            {
                j = 0;
                if ( ++i >= row )
                {
                    break;
                }
            }
        }
    }
    fclose(fp);
}
for ( i = 0; i < row; i++ )
{
    for ( j = 0; j < col; j++ )
    {
        putchar( array[i][j]);
    }
    putchar('\n');
}
free(array);
array=NULL;
return 0;
}

Here is my input file

IO.txt

 0  0   0   0   0   0   0

 0  0   1   0   2   0   0

 0  1   0   4   3   6   0

 0  0   4   0   0   5   0

 0  2   3   0   0   7   8

 0  0   0   0   8   0   9

 0  0   0   0   8   9   0

See http://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong — synchronizer, Feb 18 '17 at 05:29
What does the debugger tell you when you step through the code? — Ken White, Feb 18 '17 at 05:29
Why the downvotes & close vote? As always, of course, with explanation. — Mawg says reinstate Monica, Feb 18 '17 at 11:02

score 3 · Answer 1 · 2017-02-26T11:29:12.210

In this code:

for(int k=0;k<row;k++){
    array[c] = malloc(sizeof(char) * col);
}

You should be using k, not c to access array. c is another variable entirely.

Your compiler should have warned you about this. Always take heed of warnings:

io.c: In function ‘main’:
io.c:7:9: warning: unused variable ‘k’ [-Wunused-variable]
     int k;
         ^

Also, sizeof(char) is explictly 1, so you never need to specify it.

So the loop should look like this:

for(int k=0;k<row;k++){
    array[k] = malloc(col);
}

Also, you're forgetting to free the elements of array before you free array itself. You should do something like this:

for (int k=0; k<row; k++){
    free(array[k]);
}

Also, you're not counting columns correctly. This code:

if(c=='\t')
    nt++;
col++;

Will increment col every time through the loop, because the col++ doesn't fall within the if(c=='\t'). You need braces:

if (c =='\t') {
    nt++;
    col++;
}

Also, you've forgotten to close and then reopen your file, or seek back to the beginning, before you read it a second time. The if(fp) doesn't do anything for you. You should do this:

/* Close and then reopen the file */
fclose(fp);
fp = fopen(fopen("IO.txt", "r"));

Or this:

/* Seek to the beginning of the file */
fseek(fp, 0, SEEK_SET);

Also, you forgot to initalise i and j to 0. The compiler won't do it for you, so you need:

int c, i = 0, j = 0, row, col, nl, cr, nt;

Also, you're not counting columns or rows correctly. It's not very reliable to count rows by carriage returns, because there may not be a carriage return on the last line of the file, but assuming there is, initialise row to 0, and then the column calculation is:

col = (col / row) + 1;

Also, you're forgetting to check for tabs when you read the file the second time. The condition to add characters to your arrays should be:

if ( c != '\n' && c != '\r' && c != '\t')

That's all of the logical problems. The rest is just hygiene and style: check that the file opened successfully, check the result of malloc(), etc.

segmentation fault(core dumped) error while reading array from a input file

1 Answers1