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From: "vincent-srcware at vinc17 dot net"
 <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug stdio/30647] New: scanf functions wrong on nan()
Date: Mon, 17 Jul 2023 15:30:06 +0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: stdio
X-Bugzilla-Version: 2.37
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D30647

            Bug ID: 30647
           Summary: scanf functions wrong on nan()
           Product: glibc
           Version: 2.37
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: stdio
          Assignee: unassigned at sourceware dot org
          Reporter: vincent-srcware at vinc17 dot net
  Target Milestone: ---

On a string input containing "nan()" with parentheses (possibly with
n-char-sequence), the scanf functions assume that the subject sequence is j=
ust
"nan". Note that strtod is correct, i.e. it takes the parentheses into acco=
unt.

Consider the following testcase:

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

static void test_strtod (const char *s)
{
  char *endptr;
  double d;

  printf ("strtod test on %s\n", s);
  d =3D strtod (s, &endptr);
  printf ("d =3D %g \"%s\"\n", d, endptr);
}

int main (void)
{
  int r;
  double a, b, c;

  test_strtod ("nan*");
  test_strtod ("nan()*");

  r =3D sscanf ("nan nan() 1", "%lf%lf%lf", &a, &b, &c);
  printf ("sscanf return value: %d\n", r);
  if (r >=3D 1)
    printf ("a =3D %g\n", a);
  if (r >=3D 2)
    printf ("b =3D %g\n", b);
  if (r >=3D 3)
    printf ("c =3D %g\n", c);

  r =3D fscanf (stdin, "%lf%lf%lf", &a, &b, &c);
  printf ("fscanf return value: %d\n", r);
  if (r >=3D 1)
    printf ("a =3D %g\n", a);
  if (r >=3D 2)
    printf ("b =3D %g\n", b);
  if (r >=3D 3)
    printf ("c =3D %g\n", c);
  return 0;
}

I get the following output with GNU libc 2.31 and 2.37 on Debian:

$ printf "nan nan() 1" | ./naninput
strtod test on nan*
d =3D nan "*"
strtod test on nan()*
d =3D nan "*"
sscanf return value: 2
a =3D nan
b =3D nan
fscanf return value: 2
a =3D nan
b =3D nan

instead of

strtod test on nan*
d =3D nan "*"
strtod test on nan()*
d =3D nan "*"
sscanf return value: 3
a =3D nan
b =3D nan
c =3D 1
fscanf return value: 3
a =3D nan
b =3D nan
c =3D 1

(as obtained with MacOS X 12.6 and Android 13).

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