How to test whether a string is a valid number?

[Peng Yu]

Hi,

I want to know whether a string is a valid number. But it seems typeof
is not appropriate for it? Is there something available in awk that
can tell whether a string is a valid number? Thanks.

$ awk -v x=5 -e  'BEGIN { print typeof(3.5),typeof(x) }'
number strnum

-- 
Regards,
Peng