Date: Fri, 29 Sep 2000 14:25:31 +0200
From: "Eli Zaretskii" <eliz AT is DOT elta DOT co DOT il>
Sender: halo1 AT inter DOT net DOT il
To: djgpp-workers AT delorie DOT com
Message-Id: <2561-Fri29Sep2000142530+0300-eliz@is.elta.co.il>
X-Mailer: Emacs 20.6 (via feedmail 8.2.emacs20_6 I) and Blat ver 1.8.5h
Subject: scanf and invalid FP fields
Reply-To: djgpp-workers AT delorie DOT com

Consider the program below.  It is a variant of one of the examples in
the Draft C9X Standard (example 3 on page 271).

The issue I want to raise is when this program is presented with the
last line from that example (see page 272):

     100ergs of energy

Since the format is "%f%20s of %20s", I think this should store 100 in
the float variable that corresponds to the %f conversion specifiers,
and leave the following `e' for the char [] variable which is
converted by %20s.

Our current implementation of _doscan indeed stores 100 in the FP
variable, but swallows `e', and stores only "rgs" in the char []
variable.  I think this is wrong, since "100e" is not a valid FP
number.

However, the Draft says that the conversion should fail entirely,
because "100e" fails to match "%f".  This seems wrong to me, although
I did write a version of _doscan which behaves like that.

To make this even more interesting, I ran the test program on DJ's
Irix box and his Red Hat machine.  On Irix, the FP variable gets
assigned 100, and the char [] variable gets "ergs" copied into it.
However, Red Hat works exactly like DJGPP's libc does.

So, the question is: should we fix _doscan, and if so, how?  I'd like
to hear opinions.

Here's the test program I used.  Perhaps people could run it on more
systems, including on different Linux releases, and see what they get.

#include <stdio.h>

int main (void)
{
  int count;
  float quant;
  char units[21], item[21];

  do {
    int c;
    count = fscanf (stdin, "%f%20s of %20s", &quant, units, item);
    printf ("count: %d quant: %f units: %s item: %s\n",
	    count, quant, units, item);
    printf ("buffered chars: '");
    while ((c = getc (stdin)) != '\n' && c != EOF)
      putc (c, stdout);
    printf ("'\n");
  } while (!feof (stdin) && !ferror (stdin));

  return 0;
}