I'm trying to add formatted output to my decimal arithmetic module. Decimals should format like floating point, using 'E', 'F' and 'G', etc.

I would expect a format string like "%9.6e" to parse as width = 9, precision = 6, using exponential notation.

In std.format there is a FormatSpec struct that looks as if it will do the parsing for me. As far as I can tell the usage is:

     auto spec = std.format.FormatSpec!char("9.6e");
     writeln("fmtspec = ", fmtspec);

But it doesn't do what I think it should do.

The output of the method is:

fmtspec = address = 1637116
width = 0
precision = 2147483646
spec = s
indexStart = 0
indexEnd = 0
flDash = false
flZero = false
flSpace = false
flPlus = false
flHash = false
nested =
trailing = 9.6e

The width field should be 9, the precision field should be 6, and the spec field should be 'e'. Instead it seems to disregard the input string and return a default FormatSpec, with only the 'trailing' field populated, containing the input.

What am I missing here? I've tried variations -- "%9.6e", "s", "%s", etc, but the input is always relegated to the trailing field.

Paul

* James Miller <james@aatch.net> [2012-04-13 19:16:48 +1200]:
> * Paul D. Anderson <paul.d.removethis.anderson@comcast.andthis.net> [2012-04-13 07:50:31 +0200]:
> > I'm trying to add formatted output to my decimal arithmetic module. Decimals should format like floating point, using 'E', 'F' and 'G', etc.
> > 
> > I would expect a format string like "%9.6e" to parse as width = 9, precision = 6, using exponential notation.
> > 
> 
> Hey Paul, so some investigation has led me to believe that FormatSpec is really just for internal usage. The documentation is a bit misleading (to the point of being possibly completely false).
> 
> FormatSpec, AFAICT, is essentially just a parser for the standard format specifier, but its not very clear as to proper usage. I'm going to try to improve it and submit a pull request, until then looking at the source code for std.format should give you some idea of how to best use it.
> 
> --
> James Miller
> 

So I made the pull request, the documentation you need to read is here:

https://github.com/Aatch/phobos/commit/cda3c079ee32d98a017f88949c10097840baa075

Hopefully it helps.

--
James Miller

On Friday, 13 April 2012 at 09:10:37 UTC, James Miller wrote:
<snip/>
> So I made the pull request, the documentation you need to read is here:
>
> https://github.com/Aatch/phobos/commit/cda3c079ee32d98a017f88949c10097840baa075
>
> Hopefully it helps.
>
> --
> James Miller

Thanks. That did the trick.

Paul