Converting Unicode characters into the equivalent ASCII ones

问题

I need to "flatten out" a number of Unicode strings for the purposes of indexing and searching. For example, I need to convert GötheФ€ into ASCII. The last two characters have no close representations in ASCII so it's Ok to discard them completely. So what I expect from

echo iconv("UTF-8", "ASCII//TRANSLIT//IGNORE", "GötheФ€");

is Gothe but instead it outputs Gothe?EUR.

In addition to letters, I'd also like all the variety of Unicode numerals and punctuation marks, such as periods, commas, dashes, slashes etc. to be replaced by their closest ASCII counterparts, which is something ASCII//TRANSLIT//IGNORE in iconv function does already but not without producing some garbage output for the Unicode characters for which it's not able to find any ASCII replacements. I'd like such characters to be totally ignored.

How do get the expected result? Is there a better way, perhaps using intl library?

回答1:

You've picked a hard problem. It is better to tell the user entering Unicode characters to transliterate ASCII themselves. Doing it for them will only upset them when they disagree with your transliteration.

Anything you do will likely be jarring and offensive to people who place great meaning on Diacritics: http://en.wikipedia.org/wiki/Diacritic

No matter what transliteration strategy you use, you will not please everyone, since different people prescribe different meanings to different characters. A transliteration that delights one person will enrage another. You won't make everyone happy unless you let everyone use whatever character they want in Unicode.

But life is jarring and offensive, so off we go:

This PHP Code:

function toASCII( $str )
{
    return strtr(utf8_decode($str),
        utf8_decode(
        'ŠŒŽšœžŸ¥µÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖØÙÚÛÜÝßàáâãäåæçèéêëìíîïðñòóôõöøùúûüýÿ'),
        'SOZsozYYuAAAAAAACEEEEIIIIDNOOOOOOUUUUYsaaaaaaaceeeeiiiionoooooouuuuyy');
}

What the above PHP function does is replace each Unicode character in the first parameter of utf8_decode and replaces it with the corresponding character in the second parameter of utf8_decode.

For example the Unicode À is transliterated to ASCII A, and the å is converted to a. You'll have to specify this for every single Unicode character that you believe transliterates to an ASCII character. For the others, remove them or run them through another transliteration algorithm.

There are 95,221 other characters that you will have to look at which might transliterate to ASCII. It becomes an existential game of "When is an A no longer an A?". What about the Klingon characters and the road-map signs that kind of look like an A? The fish character kind of looks like an a. Who is to say what is what?

This is a lot of work, but if you are cleaning database input, you have to create a white list of characters and block out the other barbarians, keeping them out at the moat, it's the only reliable way.

回答2:

This php.net comment on the intl Normalizer functionality may be of use:

来源：https://stackoverflow.com/questions/14814547/converting-unicode-characters-into-the-equivalent-ascii-ones