Check if value read from file is a number or string

user_1552004 0
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I'm reading values from a file. These values could be strings or numbers - I don't know which beforehand - and I'd like to determine the data type after reading. My initial thought was to read in values as a string, cast as a number and then back to a string again and check if this is equal to the original value. For example,

a = "10.5"

if tostring(tonumber(a)) == a then
  print("It's a number!")
  print(tostring(tonumber(a)))
end

-- It's a number!
-- 10.5

This works fine for the given example, but if I change a = "10.50" then I run into problems because tostring(tonumber("10.50")) becomes 10.5 rather than 10.50.

I could do some cleaning and remove trailing zeros after reading from file, which is fine and totally doable, and then use the above code, but I wondered if there is an idiomatic way in Lua of checking type of a value that is read in from file?

lua
1 Answers
if tonumber(a) then
  print("It's a number!")
else
  print("It's not a number!")
end

Why do you print(tostring(tonumber(a)))? just print(a)

In tostring(tonumber("10.50")), tostring will mess up the formatting. If you want to have a specific formatting use string.format instead. If you want to maintain the original formatting just print a as is.

user_28581700
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