Sprintf in Ruby

Question

Sort of a quick question. I'm writing:

puts "%.3f %.4f %.5f" % [3.998877, 3.998877, 3.998877]

and get the following output:

3.999 3.9989 3.99888

sprintf simply rounds the numbers. How do I restrict that rounding?

Answer 1

>> 3.998877.to_s[/^\d+\.\d{3}/].to_f
=> 3.998
>> 3.998877.to_s[/^\d+\.\d{4}/].to_f
=> 3.9988

Answer 2

>> def truncN f, digits
>>    t = 10.0 ** digits
>>    "%.#{digits}f" % ((f * t).truncate / t)
>> end
=> nil
>> n
=> 1.11181111
>> "%.3f" % n
=> "1.112"
>> truncN n, 3
=> "1.111"