Segmentation Fault (Core dumped) - where is the error?

Question

I have a basic C program that I have to do for a Personal Software Processes assignment. I'm fairly new to C so I honestly can't see where I've gone wrong. Please read through and let me know what I'm doing that's causing it to crash?

I've got to read in a file, and store the values as an array. It comes up with no compiling errors, just a segmentation fault.

#include <stdio.h>
#define array_limit   100

int main (void)

{  
  FILE *ifp;
  char *mode = "r";
  ifp = fopen("samplepopulation.txt", mode);  


  if (ifp==NULL)
  {
    printf("cannot read file \n");
  }  
  else
  {   
    int i;
    float sample; 

    float values[array_limit];
    i = 0;

    do
    {
       fscanf(ifp, "%f", &sample);
       if (!feof(ifp))
       {
          values[i] = sample;
          printf("%f \n", values[i]);
          i++;
            if (i>array_limit)
            {
               printf("File larger than allowed/n");
               break;
            }
       }

       else
       {
          printf("read complete");
       }

    } while (ifp!= EOF);     
  }

  fclose(ifp);

  return 0;
}

You have tagged this post with the C tag, but you are not declaring the variables at the beginning of your code. Take care of this kind of things... — adripanico, Mar 31 '14 at 13:51
What is `ifp != EOF` doing? ifp is a file pointer and EOF is an integer. That's not how you check for EOF. — avmohan, Mar 31 '14 at 13:52
@adripanico That's perfectly fine in C. Welcome to the year 1999. — Lundin, Mar 31 '14 at 13:52
@Lundin That's perfectly fine with the compiler. The C specification have never allowed it. — adripanico, Mar 31 '14 at 13:55
@adripanico The C standard was changed to allow it in 1999. Your C knowledge is 15 years outdated. — Lundin, Mar 31 '14 at 13:59
@Lunding I'll have to trust you because I am not able to find anything that says otherwise :) — adripanico, Mar 31 '14 at 14:06
@adripanico Read http://en.wikipedia.org/wiki/C99. "intermingled declarations and code: variable declaration is no longer restricted to file scope or the start of a compound statement (block), similar to C++" — avmohan, Mar 31 '14 at 14:08
Guys even just this throws a fault... wtf am I not seeing #include int main (void) { FILE *ifp; ifp = fopen("samplepopulation.txt", "r"); fclose(ifp); return 0; } — jesspick, Mar 31 '14 at 14:14
actually, all of those declarations are at the beginning of blocks. this is even legal in c89 — Steve Cox, Mar 31 '14 at 14:27
@user3475432: Calling `fclose()` on an illegal pointer is undefined behaviour, and you didn't check if `fopen()` succeeded, so I would guess it failed... — DevSolar, Mar 31 '14 at 14:33

HelloWorld123456789 · Answer 1 · 2014-03-31T14:00:17.720

0

Change

while (ifp!= EOF);

to

while (!feof(ifp));

Also scan from file like this:

if (fscanf(ifp, "%f", &sample)==EOF) //EOF if input failure
   break;

edited Mar 31 '14 at 14:00

answered Mar 31 '14 at 13:53

HelloWorld123456789

5,299
3
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And in addition, check the result from fscanf and see if it is EOF. The code seems to have confused when to use feof() and when to check for EOF. – Lundin Mar 31 '14 at 13:54
What if read fails with ferror? In that case feof will never be true and hence it'll be infinite loop. – avmohan Mar 31 '14 at 13:54
"The fscanf function returns the value of the macro EOF if an input failure occurs before the first conversion (if any) has completed. Otherwise, the function returns the number of input items assigned, which can be fewer than provided for, or even zero, in the event of an early matching failure." – Lundin Mar 31 '14 at 13:56
`while(!feof(ifp))` is just plain wrong, [this has been explained over, and over, and over](http://stackoverflow.com/questions/5431941/while-feof-file-is-always-wrong) – Elias Van Ootegem Mar 31 '14 at 14:31
@EliasVanOotegem But here the read error is being taken care of. So this works fine. – HelloWorld123456789 Mar 31 '14 at 14:33
1

@RikayanBandyopadhyay: `EOF` isn't an error, `ferror` isn't dealt with at all. If there really was a read-error, then checking for `feof` will get you nowhere. Besides, I think the issue here could well be `fclose(possible_null_ptr);` – Elias Van Ootegem Mar 31 '14 at 14:37

score 0 · Answer 2 · answered Mar 31 '14 at 16:54

0

Segmentation Fault (Core dumped) - where is the error?

2 Answers2