This behavior is how floating-point math works, which is not best addressed in the documentation for the formatted I/O library. We see may comments from people new to floating point who argue that there are bugs in Go's arithmetic, but it's invariably a lack of familiarity with the—admittedly rather tricky—properties of imprecise arithmetic.
-rob On Tue, Oct 11, 2022 at 9:01 AM Dante Castagnoli <dante.castagn...@gmail.com> wrote: > Thanks! > > It's not lost, though. It shows up with the %g form. > > Knowing about %g, my issue is not extant, but others might hit it. I'm > relatively new to floating point issues, and I saw numbers showing up as > integers, and it took a while to sort out what was going on, is all. > > As the behavior matches "c", I would suggest at minimum making the > documentation clearer. > > https://go.dev/play/p/WBlf3jltimr > > On Monday, October 10, 2022 at 10:27:00 AM UTC-7 Brian Candler wrote: > >> Whilst Go handles constants with arbitrary precision AFAIK, precision is >> lost once values are assigned to a float64 variable (or passed as an >> argument to a function). There are only 53 bits of precision in the >> "mantissa". >> >> For more info, you might find this helpful: >> https://0.30000000000000004.com/ >> >> On Monday, 10 October 2022 at 17:48:56 UTC+1 dante.ca...@gmail.com wrote: >> >>> Hi, >>> >>> I'm wondering what folks think about the behavior of %f and precision. >>> >>> The go fmt documentation states: >>> > For floating-point values, width sets the minimum width of the field >>> and precision sets the number of places after the decimal, >>> >>> What I discovered is there is rounding going on in %f as shown below. >>> >>> https://go.dev/play/p/23AfRtwOqcD >>> >>> I found this behavior as I'm converting floats to integers, and was >>> testing fine regions between digits, and experienced the behavior. I >>> didn't expect it. >>> >>> I expected the behavior of printing "n" characters of a string. >>> However, I note that "c" behaves the same way: >>> >>> $ cat math.c >>> #include<stdio.h> >>> int main(int argc, char *argv[]) { >>> printf("%0.3f\n", 0.9999999999); >>> } >>> $ ./math >>> 1.000 >>> $ >>> >> -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/4a15ac2c-e30d-4d6e-be8f-251996fb01cen%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/4a15ac2c-e30d-4d6e-be8f-251996fb01cen%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOXNBZRq9U4O-cCFxugZSFmJf-z0rR10HAE5Do2HGDPB30nuXQ%40mail.gmail.com.
