How Can I Detect the Characters Defined in a Font?
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I'm making a simple tool to help with css icon fonts.

Currently, it takes a specified, wingdings-style font, and represents it as it appears for every unicode number, side-by-side with a standard system font (arial, for example) at the moment I'm going from unicode numbers 33-255.

As those familiar with fonts and character encoding will have already guessed, a lot of these places will be empty. Here's an example:
![enter image description here][1]

As you can see, the characters which are actually worth showing for this font are in the minority, and many characters in this unicode range don't even show up for the default sans-serif font. This isn't critical stuff, all the usable characters are shown anyway, but purely out of curiosity, I'd love to know if there's a way to tell which characters are represented in a font. Does anybody know a solution?

Ideally, a server-side solution is preferred, any language you like. However, any solution at all would be valuable.

For the curious, my existing code is up on github: [Font Looper][2]

I hope the flat-file presentation doesn't offend anyone too much, I'm trying to keep this one lean and mean.


  [1]: http://i.stack.imgur.com/5EMeY.png
  [2]: https://github.com/daveycakes/font-looper