How to convert a string to strnum?

[Peng Yu]

https://www.gnu.org/software/gawk/manual/html_node/Variable-Typing.html

$ awk -e 'BEGIN { x="1e6"; print typeof(x), typeof(strtonum(x)) }'
string number

I can only convert a string to a number. But I don't find a way to
convert a string to a strnum. Is there a way to do so?

-- 
Regards,
Peng