# How to check if a string is a integer? **URL:** \ **Category:** Ruby\ **Created:** [June 4, 2007, 3:39pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909 "2007-06-04T15:39:44Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 3:39pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/1 "2007-06-04T15:39:44Z")
How to check if a string is a integer ? After seached in google, I can’t find any information. All ISINTEGER function is about Javascript. Thank you. ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 3:46pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/2 "2007-06-04T15:46:45Z")
w wg wrote: > How to check if a string is a integer ? > > After seached in google, I can’t find any information. All ISINTEGER > function is about Javascript. > > Thank you. You can use Integer(), it raises if the String passed is not an integer. In case Integer() confuses you: that’s Kernel#Integer(), a method, not the class Integer. Also you can use a regex, e.g. str =~ /\A[±]?\d+\z/ Regards Stefan ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 3:49pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/3 "2007-06-04T15:49:47Z")
On 04/06/07, w wg [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > How to check if a string is a integer ? You can use either the String#to\_i or Kernel#Integer methods irb(main):001:0\> “1234”.to\_i =\> 1234 irb(main):002:0\> “123A”.to\_i =\> 123 irb(main):003:0\> “A123”.to\_i =\> 0 irb(main):004:0\> Integer(“A1234”) ArgumentError: invalid value for Integer: “A1234” from (irb):4:in `Integer' from (irb):4 irb(main):005:0> Integer("1234A") ArgumentError: invalid value for Integer: "1234A" from (irb):5:in `Integer’ from (irb):5 irb(main):006:0\> Integer(“1234”) =\> 1234 irb(main):007:0\> Farrel ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 3:56pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/4 "2007-06-04T15:56:16Z")
w wg wrote: > How to check if a string is a integer ? > > After seached in google, I can’t find any information. All ISINTEGER > function is about Javascript. > > Thank you. Call the is\_a? (or kind\_of?) method on the object: 123.is\_a? Integer =\> true ‘David’.is\_a? Integer =\> false David > **[Ruby on Windows](http://rubyonwindows.blogspot.com)** > > On using the Ruby programming language on the Microsoft Windows platform ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 4:02pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/5 "2007-06-04T16:02:48Z")
Thank you, it works. How did you find the Integer method of class Kernel ? I typed “ri Kernel”, but I can’t find any Kernel’s class method. 2007/6/4, Farrel L. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 4:05pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/6 "2007-06-04T16:05:48Z")
On 04/06/07, David M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > w wg wrote: > 123.is\_a? Integer > =\> true > ‘David’.is\_a? Integer > =\> false That won’t work irb(main):001:0\> “123”.is\_a? Integer =\> false Farrel ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 4:39pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/7 "2007-06-04T16:39:53Z")
Hi, Am Montag, 04. Jun 2007, 22:46:45 +0900 schrieb Stefan R.: > w wg wrote: > > > How to check if a string is a integer ? > > Also you can use a regex, e.g. str =~ /\A[±]?\d+\z/ In many cases it’s useful to test for hex representations as well. Something like: class String def as\_uint case self when /\A0x[0-9a-f]+\z/i then hex when /\A0b[0-1]+\z/ then bin when /\A0[0-7]+\z/ then oct when /\A(?:0|[1-9]\d\*)\z/ then to\_i end end end There should be a combination of Kernel#eval and $SAFE, too. Bertram ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 6:00pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/8 "2007-06-04T18:00:11Z")
Bertram S. wrote: > Hi, > > Am Montag, 04. Jun 2007, 22:46:45 +0900 schrieb Stefan R.: > > > w wg wrote: > > > > > How to check if a string is a integer ? > > > > Also you can use a regex, e.g. str =~ /\A[±]?\d+\z/ > > In many cases it’s useful to test for hex representations as > well. Something like: In those cases I’d even more use Integer(). It accepts about all representations of Integers ruby itself understands. It is probably much faster than a case/when, you also will have the value converted to an integer afterwards, which you most probably want anyway. Regards Stefan ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 4:50pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/9 "2007-06-04T16:50:19Z")
Farrel L. wrote: > On 04/06/07, David M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > w wg wrote: > > 123.is\_a? Integer > > =\> true > > ‘David’.is\_a? Integer > > =\> false > > That won’t work > > irb(main):001:0\> “123”.is\_a? Integer > =\> false > > Farrel Of course not. Duh! My apologies. Perhaps I shouldn’t post before my first cup of tea. David ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 5, 2007, 3:46am UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/10 "2007-06-05T03:46:34Z")
From: w wg [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)] : # I typed “ri Kernel”, but I can’t find any Kernel’s class method. ## C:\family\ruby\>qri integer --------------------------------------------------------- Kernel#Integer Integer(arg) =\> integer ``` Converts _arg_ to a +Fixnum+ or +Bignum+. Numeric types are converted directly (with floating point numbers being truncated). If _arg_ is a +String+, leading radix indicators (+0+, +0b+, and +0x+) are honored. Others are converted using +to_int+ and +to_i+. This behavior is different from that of +String#to_i+. Integer(123.999) #=> 123 Integer("0x1a") #=> 26 Integer(Time.new) #=> 1049896590 ``` same w qri kernel#integer ---
**Author:** ![w\_wg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/w/7ba0ec/32.png) [@w\_wg](https://www.ruby-forum.com/u/w_wg)\ **Post date:** [June 4, 2007, 6:06pm UTC](https://www.ruby-forum.com/t/how-to-check-if-a-string-is-a-integer/105909/11 "2007-06-04T18:06:03Z")
Hi, Am Dienstag, 05. Jun 2007, 01:00:10 +0900 schrieb Stefan R.: > In those cases I’d even more use Integer(). It accepts about all > representations of Integers ruby itself understands. Aah! I did not know that. Cool. Thanks. Bertram