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Date: Fri, 02 Sep 2011 21:54:39 -0700
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Subject: Re: Solving the Floating-Point Goldilocks Problem!
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On 9/2/11 12:08 PM, Stephen Fuld wrote:
> On 9/2/2011 8:46 AM, Robert Wessel wrote:
>
> snip
>
>> But I've always though that some additional formatting in printf
>> formatting strings would be an obvious feature to add to C.

Checkout plan9's fmtinstall(). Allows you to provide your own formatting functions.
For instance, in the example below %X is added to print a user defined type.

typedef struct { double    r, i; } Complex;

int
Xfmt(Fmt *f)
{
	Complex c;
	c = va_arg(f–>args, Complex);
	return fmtprint(f, "(%g,%g)", c.r, c.i);
}

main(...)
{
	Complex x = (Complex){ 1.5, –2.3 };
	fmtinstall('X', Xfmt);
	print("x = %X\n", x);
}

>
>
> Yes, of course. While the full functionality of picture clauses might be nice, A small subset would
> go a long way. The single thing I would most like to see is to make it easy to print numbers with
> separators every three characters. I get so frustrated when I see things like the output of a
> profiling program say a routine was executed
>
> 34587706689349 times.
>
> It sure makes it hard to read and there is no excuse for that. I realize there are issues with
> commas versus spaces as separators, but these could be overcome. I would like to see the "digit
> separated" format be another editing code so it would be trivial for a programmer to specify it
> without having to create a full picture clause, which would be many more characters to input and
> thus less frequently used.
>
> The second most useful feature I suspect would be a floating currency indicator. Once you get beyond
> those two, I think the utility falls off pretty quickly, though the ability to specify that negative
> values should be a different color might be nice. But I suspect that say the ability to have CR or
> DB automatically appended to the value depending on sign is pretty unimportant.
>
> But digit separators would help in a lot of places.

Ansi C has now has a ' (single quote) flag which prints a number
in a locale specific manner. For instance (on Linux):

$ cat xx.c
#include <locale.h>
#include <stdio.h>
main(int argc, char** argv)
{
         setlocale(LC_ALL, argv[1]);
         printf("%'f\n", 34587706689349.125);
}
$ cc xx.c
$ a.out en_DK
34.587.706.689.349,125000
$ a.out en_GB
34,587,706,689,349.125000
$ a.out en_IN
3,45,87,70,66,89,349.125000

Of course, the challenge is in making programmers use this!