Floating point string representation
Johann Höchtl
When I do a Printf("%.4f", ...) it would return "12.0000"
In such a case I would like to have a clear "12" printed out. Is there
a format specifier which will omit the suffix in case it would be all
zero or do I have to write my own formating routine?
Johann
Andrew Gerrand
If you just use %f (or Print()) to format a float, the default is to
provide as many decimal places as are required to describe the value
precisely.
Andrew
Andrew Gerrand
Actually I'm mistaken: what I said is true of %v and %g but not %f.
Andrew
Johann Höchtl
On Feb 14, 10:36 pm, Andrew Gerrand <a...@golang.org> wrote:
http://goo.gl/pU4Ad
> Andrew
Johann Höchtl
package main
import "fmt"
type BMNCoord struct {
Right, Height, RelHeight float64
}
func NewBMNCoord(r, h, rh float64) *BMNCoord {
return &BMNCoord{Right:r, Height:h}
}
func (co *BMNCoord) String() string {
return fmt.Sprintf("%f %f", co.Right, co.Height)
}
func main() {
f := 2000
fmt.Println(f)
coord := NewBMNCoord(2000.0, 4000.0, 0)
fmt.Println(coord)
}
/* Output is:
2000
2000.000000 4000.000000
*/
Why doesn't the second printf hidden in a Sprintf not cut away the all
zero suffixes?
> > Andrew
Andrew Gerrand
> Why doesn't the second printf hidden in a Sprintf not cut away the all
> zero suffixes?
Use %v instead of %f.
Andrew
Johann Höchtl
On Feb 14, 11:10 pm, Andrew Gerrand <a...@golang.org> wrote:
>
> > Why doesn't the second printf hidden in a Sprintf not cut away the all
> > zero suffixes?
>
> Use %v instead of %f.
>
suffix and truncates to two places after the suffix. If the suffix
would be all zero, it is completely discarded.
0.5 is rounded towards zero.
This should be documented.
> Andrew
David Roundy
> On Feb 14, 11:10 pm, Andrew Gerrand <a...@golang.org> wrote:
>> On 14 February 2011 17:05, Johann Höchtl <johann.hoec...@gmail.com> wrote:
>>
>> > Why doesn't the second printf hidden in a Sprintf not cut away the all
>> > zero suffixes?
>>
>> Use %v instead of %f.
>>
> "%.3v" is doing what I want as it rounds at the third place after the
> suffix and truncates to two places after the suffix. If the suffix
> would be all zero, it is completely discarded.
In C or C++ (and most languages that support C-style printf), %.3g
will do what you want, and this also works in go. I just mention
this, since it's not unlikely that you'll end up wanting to do the
same thing in some other language some day, and %v is specific to go.
Also, I consider using %g to be more clear, since it documents within
the string that you expect a floating-point value.
> This should be documented.
I agree.
--
David Roundy
Russ Cox
Yes, and 1.5 is rounded towards two.
It's the standard rules.
Johann Höchtl
output should not be in scientific notation. As such, %g is not save,
as %g MAY print in scientific notation.
Take a look at this:
http://pastebin.com/2gh9was6
The output is
2000
2e+06 4e+07
70 30 <- <-- This line is good
but I would like it to be
2000000.1 40000000
70 30 <-- This line is good
(or 2000000.1=2= 40000000, depending on what the "2" in %.2g actually
means)
Changing the format specifier back to %f prints the all zero suffix.
Johann
Russ Cox
In fact package strconv does not even do what you are asking.
The closest you can get is to use
s := fmt.Sprintf("%.6f", f)
n := len(s)
for n > 0 && s[n-1] == '0' {
n--
}
if n > 0 && s[n-1] == '.' {
n--
}
s = s[:n]
If you put this in a String method on your own type then
you can use it to print your values by converting them to
that type in the call to fmt.Println or any of the other printers.
Russ
Johann Höchtl
On Feb 15, 11:14 pm, Russ Cox <r...@golang.org> wrote:
> There is no way to do what you are asking with a format verb.
> In fact package strconv does not even do what you are asking.
>
> The closest you can get is to use
>
> s := fmt.Sprintf("%.6f", f)
> n := len(s)
> for n > 0 && s[n-1] == '0' {
> n--
> }
> if n > 0 && s[n-1] == '.' {
> n--
> }
> s = s[:n]
>
such a formatting flag would be useful.
Russ Cox
> such a formatting flag would be useful.
You can extend the formatting behavior yourself by defining
your own floating point type that has a String or Format method.
(See godoc fmt.)
Russ