[Bug stdio/30647] New: scanf functions wrong on nan()

[Bug stdio/30647] New: scanf functions wrong on nan()

[vincent-srcware at vinc17 dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=30647

            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 just
"nan". Note that strtod is correct, i.e. it takes the parentheses into account.

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

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

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

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

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

instead of

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

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

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug stdio/30647] scanf functions wrong on nan()

[vincent-srcware at vinc17 dot net]

https://sourceware.org/bugzilla/show_bug.cgi?id=30647

--- Comment #1 from Vincent Lefèvre <vincent-srcware at vinc17 dot net> ---
Note that if the string starts with "nan(" but does not match
nan(n-char-sequence_opt), then scanf must reject the conversion (after reading
the longest prefix).

Examples:
* "nan(foo" (no closing parenthesis)
* "nan(a b)" (the space is not valid in n-char-sequence)

Currently it doesn't, because it stops at "nan" (it does not read the longest
prefix). These cases are similar to issues mentioned in bug 12701, but
currently this is not the same bug.

-- 
You are receiving this mail because:
You are on the CC list for the bug.

[Bug stdio/30647] scanf functions wrong on nan()

[carlos at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30647

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |carlos at redhat dot com
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2024-04-30
             Status|UNCONFIRMED                 |NEW

--- Comment #2 from Carlos O'Donell <carlos at redhat dot com> ---
I agree this does look like a conformance issue with the scanf family of
functions using __vfscanf_internal() implemetnation.

-- 
You are receiving this mail because:
You are on the CC list for the bug.