Bug in printf ?

Thu Jun 30 12:14:00 GMT 2005

haro@kgt.co.jp wrote:
> ::How come "0.125" gets printed as "0.12", and not "1.3"?
> ^^^ "0.13", off cource ;-)

Dealing with integers illustrates the matter more clearly. When
the decimal value is exactly 0.5, then printf should round to the
nearest *even* integer, as far as I know, so you should get
 0 -> 0
 0.5 -> 0
 1 -> 1
 1.5 -> 2
 2 -> 2
 2.5 -> 2
 3 -> 3
 3.5 -> 4
 4 -> 4
 4.5 -> 4
 5 -> 5
Now I realize that Cygwin's printf doesn't get it right, because
 seq 0 .5 5 | while read x; do printf '%-3s -> %.0f\n' $x $x; done
gives
 0 -> 0
 0.5 -> 1
 1 -> 1
 1.5 -> 1
 2 -> 2
 2.5 -> 2
 3 -> 3
 3.5 -> 3
 4 -> 4
 4.5 -> 4
 5 -> 5
Both Solaris' /bin/printf and Perl's printf() give the right
output.
In your examples there is also an additional issue, which is how
numerical values are represented. Here is Perl:
 seq .105 .01 .155 | while read x; do printf '%-5s -> %.2f\n' $x $x; done
 0.105 -> 0.10
 0.115 -> 0.12
 0.125 -> 0.12
 0.135 -> 0.14
 0.145 -> 0.14
 0.155 -> 0.15
They all seem correct expect the last one. The reason why 0.155
becomes 0.15 and not 0.16 is that 0.115 can not be represented
exactly. It is represented as a number which is slightly
*smaller* than 0.155, so it becomes 0.15 after rounding.
Peter
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