Re: strange issue reading /dev/null

[Sean C. Farley]

On Thu, 7 Aug 2008, Gabor Kovesdan wrote:

Hello,

I'm wondering why fgetc() returns 0xff if called with /dev/null:

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

int
main(void)
{
      int      c;
      FILE    *f;

      f = fopen("/dev/null", "r");

      if (c != EOF)
              printf("%c\n", fgetc(f));
}

gcc foo.c
./a.out

ÿ

This causes a bug in BSD grep as /dev/null is not distinguished from
ordinary files in the code, thus I was expecting it just returned EOF,
but in reality this is not the case. How such cases should be handled?

You are testing c which has not been set.  It works OK if you set c then
do the test:

+       c = fgetc(f);
        if (c != EOF)
-               printf("%c\n", fgetc(f));
+               printf("%c\n", c);

Sean
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