Making printf do the right thing with floating point

Question

I'm trying to make printf 'do the right thing' with floating point numbers, i.e.:

• Never lose information, always print as many decimals as are needed for the exact value

• Don't print a bunch of redundant trailing zeros

• Switch to scientific notation if the output would otherwise be unreasonably large

%.20g seems to do all that, but there's one more thing I would like to get:

• If the value is an integer, do print a trailing '.0' to indicate it is a floating point number with an integer value, not a number of type integer

Is there any way to get the fourth criterion without losing any of the first three?

Answer 1

It looks like the flag "#" will at least put a period at the end. Try %#.20g.

The # flag is for example documented here: "Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written."