如何使用sprintf控制Perl中的浮点格式？

Question

I usually use %g , but it seems the number of exponent digits is system-dependent , and I can't variants like %.4g or %.2g to work (they simply produce the same results, don't they?).

What I actually would like to do is to use simple floating point representation "when possible" if the number (in absolute value) is in some range (eg 10^5 > |x| > 10^-5), otherwise use scientific notation. I also want to limit the number of digits displayed to, say, 5 (so I won't get super huge floating point numbers like 0.12345678901234567890...).

Some examples:

0.123456890 -> 0.12346

0.000000000123456 -> 1.23456e-10

Can I do that directly in sprintf or do I have to write a special wrapper?

Answer 1

No, you'd have to write a custom wrapper to get the behavior you describe: As perlfunc says:

For "g" and "G", [the precision] specifies the maximum number of digits to show, including those prior to the decimal point and those after it;

Note that leading zeros in the simple floating point representation are not counted as "digits".

There are some modules on CPAN that'll help you write a sprintf-like function. String::Sprintf is for adding a custom format or two to the regular sprintf formats. String::Formatter is for starting from scratch with a function that looks like sprintf but doesn't inherit any formats from it.