2 Replies Latest reply on Oct 28, 2007 4:31 AM by Newsgroup_User

    Annoying String to Float in AS3

    Level 7
      Hey again,

      I am working on *AS3* here.

      Problem: I have a value stored in a String. I'd like to check whether
      that String is a float. I am aware of the method parseFloat(string)
      described here:
      However, this method has annoying limitations:
      parseFloat("2.5") will be 2.5
      parseFloat(" 2.5") will be 2.5
      parseFloat("2.5garbage") will be 2.5
      parseFloat("2.5garbage3.2") will be 2.5
      it will only be NaN if the value of the string starts with a non-
      numerical character
      parseFloat("garbage2.5") will be NaN

      So doing something like that, will not work for me:
      public function isFloat : Boolean(str : String) {
      if (isNaN(parseFloat(str))) {
      return false;
      return true;

      I want to check if the string is a *real* float that is:
      isFloat("2.5") will be true
      isFloat("x2.5") will be false
      isFloat("2.5x3.2") will be false
      isFloat("2.5x") will be false
      Basically, no spaces or non-numerical characters should be allowed
      (expect the one dot '.' if required).

      I'm thinking of implementing my own isFloat method, checking character by
      character to see if the value is really a float or not. Something like
      that (quick draft, haven't tested it or compiled it):

      public function isFloat : Boolean (str : String) {
      var dotUsed : Boolean = false;
      for (var i : int = 0; i < str.length; ++i) {
      if (str.charAt(i) == '.') {
      if (!dotUsed) {
      dotUsed = true;
      } else {
      return false;
      } else if (isNaN(parseInt(str.charAt(i)))) {
      return false;

      However, I'm not happy with the runtime efficiency here. I'm sure there's
      some more efficient way to detect that a string is a float; or another
      simple method I haven't look at.

      Any thoughts?

        • 1. Re: Annoying String to Float in AS3
          Greg Dove Level 4
          You can avoid the looping test by using a regular expression. Basically the whole check could be done with a regular expression. I'd love to provide the code, but regular expressions are new to me as well. I had a play around with them and got close, but it didn't pass all the tests, so I wasn't doing something right. Someone else will post an example I'm sure.
          • 2. Re: Annoying String to Float in AS3
            Level 7
            That's a good idea actually. I wonder why I haven't though of it earlier.
            Something like that should do it:

            public function isFloat (str: String) : Boolean {
            static var re : RegExp = new RegExp('([0-9]+(\.[0-9]*)?)|(\.[0-9]+)');
            return re.test(str);

            If other ideas come up, please let me know.
            Thanks again.