Safe integer parsing in Ruby

wvdschel_2018 0
Viewed 95728

I have a string, say '123', and I want to convert it to the integer 123.

I know you can simply do some_string.to_i, but that converts 'lolipops' to 0, which is not the effect I have in mind. I want it to blow up in my face when I try to convert something invalid, with a nice and painful Exception. Otherwise, I can't distinguish between a valid 0 and something that just isn't a number at all.

EDIT: I was looking for the standard way of doing it, without regex trickery.

string-parsing integer exception ruby string
8 Answers

Ruby has this functionality built in:

Integer('1001')                                    # => 1001  
Integer('1001 nights')  
# ArgumentError: invalid value for Integer: "1001 nights"

As noted in answer by Joseph Pecoraro, you might want to watch for strings that are valid non-decimal numbers, such as those starting with 0x for hex and 0b for binary, and potentially more tricky numbers starting with zero that will be parsed as octal.

Ruby 1.9.2 added optional second argument for radix so above issue can be avoided:

Integer('23')                                     # => 23
Integer('0x23')                                   # => 35
Integer('023')                                    # => 19
Integer('0x23', 10)
# => #<ArgumentError: invalid value for Integer: "0x23">
Integer('023', 10)                                # => 23
Slartibartfast_44330

This might work:

i.to_i if i.match(/^\d+$/)
user_46150

Also be aware of the affects that the current accepted solution may have on parsing hex, octal, and binary numbers:

>> Integer('0x15')
# => 21  
>> Integer('0b10')
# => 2  
>> Integer('077')
# => 63

In Ruby numbers that start with 0x or 0X are hex, 0b or 0B are binary, and just 0 are octal. If this is not the desired behavior you may want to combine that with some of the other solutions that check if the string matches a pattern first. Like the /\d+/ regular expressions, etc.

user_7920

I had to deal with this in my last project, and my implementation was similar, but a bit different:

class NotAnIntError < StandardError 
end

class String
  def is_int?    
    self =~ /^-?[0-9]+$/
  end

  def safe_to_i
    return self.to_i if is_int?
    raise NotAnIntError, "The string '#{self}' is not a valid integer.", caller
  end
end

class Integer
  def safe_to_i
    return self
  end            
end

class StringExtensions < Test::Unit::TestCase

  def test_is_int
    assert "98234".is_int?
    assert "-2342".is_int?
    assert "02342".is_int?
    assert !"+342".is_int?
    assert !"3-42".is_int?
    assert !"342.234".is_int?
    assert !"a342".is_int?
    assert !"342a".is_int?
  end

  def test_safe_to_i
    assert 234234 == 234234.safe_to_i
    assert 237 == "237".safe_to_i
    begin
      "a word".safe_to_i
      fail 'safe_to_i did not raise the expected error.'
    rescue NotAnIntError 
      # this is what we expect..
    end
  end

end
Admin1 
someString = "asdfasd123"
number = someString.to_i
if someString != number.to_s
  puts "oops, this isn't a number"
end

Probably not the cleanest way to do it, but should work.

Paul_Wicks_850

Re: Chris's answer

Your implementation let's things like "1a" or "b2" through. How about this instead:

def safeParse2(strToParse)
  if strToParse =~ /\A\d+\Z/
    strToParse.to_i
  else
    raise Exception
  end
end

["100", "1a", "b2", "t"].each do |number|
  begin
    puts safeParse2(number)
  rescue Exception
    puts "#{number} is invalid"
  end
end

This outputs:

100
1a is invalid
b2 is invalid
t is invalid
metavida_55390
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