Re: printf "%010a" Inf/NaN and FreeBSD

[Bruno Haible]

Eric Blake wrote:
> That's now three reasons why I think FreeBSD's behavior is wrong.

OK, let's summarize (in case you want to bring it to the Austin group):

Arguments in favour of "       nan", "       inf":

  - For NaN, there is no indication of a sign or base; for Inf, there is
    no indication of a base. Even in hexadecimal mode ('a', 'A') no "0x"
    is output for NaN and Inf.
  - It's useful if strtod of the output returns (approximately) the original
    value. And
      strtod ("      -inf", NULL) = -Infinity
    whereas
      strtod ("-000000inf", NULL) = NaN

Arguments in favour of "0000000nan", "0000000inf":

  - The explanation of the flag '0' says:
      "leading zeros (following any indication of sign or base) are used
       to pad to the field width; no space padding is performed".

I don't think the sentence "A double argument representing an infinity or
NaN shall be converted in the style of an f or F conversion specifier" is
an argument in either direction, because all tested systems satisfy this
sentence. See below for a test.

Bruno


=========================== Program =============================
#include <stdio.h>
#include <stdlib.h>
double nan = 0.0 / 0.0;
double inf = 1.0 / 0.0;
double minf = -1.0 / 0.0;
int main()
{
  char buf[20];

  sprintf (buf, "%010f", -1.0);
  printf ("%s|%f\n", buf, strtod (buf, NULL));
  sprintf (buf, "%010a", -1.0);
  printf ("%s|%f\n", buf, strtod (buf, NULL));

  sprintf (buf, "%010f", nan);
  printf ("%s|%f\n", buf, strtod (buf, NULL));
  sprintf (buf, "%010a", nan);
  printf ("%s|%f\n", buf, strtod (buf, NULL));

  sprintf (buf, "%010f", inf);
  printf ("%s|%f\n", buf, strtod (buf, NULL));
  sprintf (buf, "%010a", inf);
  printf ("%s|%f\n", buf, strtod (buf, NULL));

  sprintf (buf, "%010f", minf);
  printf ("%s|%f\n", buf, strtod (buf, NULL));
  sprintf (buf, "%010a", minf);
  printf ("%s|%f\n", buf, strtod (buf, NULL));

  return 0;
}
================== Result on glibc-2.3.6, glibc-2.5 ===============
-01.000000|-1.000000
-0x0001p+0|-1.000000
       nan|nan
       nan|nan
       inf|inf
       inf|inf
      -inf|-inf
      -inf|-inf
============================ Result on FreeBSD 6.1 ================
-01.000000|-1.000000
-0x0001p+0|-1.000000
0000000nan|0.000000
0000000nan|0.000000
0000000inf|0.000000
0000000inf|0.000000
-000000inf|-0.000000
-000000inf|-0.000000
===================================================================