RFC: 6178739 - Formatter - Zero padding flag with zero width

Brian Burkhalter brian.burkhalter at oracle.com
Wed Jun 26 18:00:40 UTC 2013

For further comparison, the man page for PRINTF(1) on Mac OS 10.7.5 states

     Field Width:
             An optional digit string specifying a field width; if the output
             string has fewer characters than the field width it will be
             blank-padded on the left (or right, if the left-adjustment indi-
             cator has been given) to make up the field width (note that a
             leading zero is a flag, but an embedded zero is part of a field

and that for printf(3) on Ubuntu 12.04

   The field width
       An  optional decimal digit string (with nonzero first digit) specifying
       a minimum field width.  If the converted  value  has  fewer  characters
       than  the  field  width,  it will be padded with spaces on the left (or
       right, if the left-adjustment flag has been given).  Instead of a deci‐
       mal  digit  string one may write "*" or "*m$" (for some decimal integer
       m) to specify that the field width is given in the next argument, or in
       the m-th argument, respectively, which must be of type int.  A negative
       field width is taken as a '-' flag followed by a positive field  width.
       In  no case does a nonexistent or small field width cause truncation of
       a field; if the result of a conversion is wider than the  field  width,
       the field is expanded to contain the conversion result.

Ubuntu Linux and Mac OS X show the same behavior for

    printf("%0.4f\n", 56789.456789F);

which is to print


This looks as if the default width is taken to be zero. Adopting this behavior for Formatter however would look to be in violation of its specification

'0'	'\u0030'	Requires the output to be padded with leading zeros to the minimum field width following any sign or radix indicator except when converting NaN or infinity. If the width is not provided, then a MissingFormatWidthException will be thrown.

On Jun 26, 2013, at 10:31 AM, Brian Burkhalter wrote:

> "A leading zero in the width value is interpreted as the zero-padding flag mentioned above […]." [1]

[1] https://en.wikipedia.org/wiki/Printf#Format_placeholders

More information about the core-libs-dev mailing list