Truncate a multibyte String to n chars

Question

I am trying to get this method in a String Filter working:

public function truncate($string, $chars = 50, $terminator = ' …');

I'd expect this

$in  = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWYXZ1234567890";
$out = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUV …";

and also this

$in  = "âãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿĀāĂ㥹ĆćĈĉĊċČčĎďĐđĒēĔĕĖėĘęĚěĜĝ";
$out = "âãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿĀāĂ㥹ĆćĈĉĊċČčĎďĐđ …";

That is $chars minus the chars of the $terminator string.

In addition, the filter is supposed to cut at the first word boundary below the $chars limit, e.g.

$in  = "Answer to the Ultimate Question of Life, the Universe, and Everything.";
$out = "Answer to the Ultimate Question of Life, the …";

I am pretty certain this should work with these steps

• substract amount of chars in terminator from maximum chars
• validate that string is longer than the calculated limit or return it unaltered
• find the last space character in string below calculated limit to get word boundary
• cut string at last space or calculated limit if no last space is found
• append terminator to string
• return string

However, I have tried various combinations of str* and mb_* functions now, but all yielded wrong results. This can't be so difficult, so I am obviously missing something. Would someone share a working implementation for this or point me to a resource where I can finally understand how to do it.

Thanks

P.S. Yes, I have checked http://stackoverflow.com/search?q=truncate+string+php before :)

Answer 1

I don't usually like to just code an entire answer to a question like this. But also I just woke up, and I thought maybe your question would get me in a good mood to go program for the rest of the day.

I didn't try to run this, but it should work or at least get you 90% of the way there.

function truncate( $string, $chars = 50, $terminate = ' ...' )
{
    $chars -= mb_strlen($terminate);
    if ( $chars <= 0 )
        return $terminate;

    $string = mb_substr($string, 0, $chars);
    $space = mb_strrpos($string, ' ');

    if ($space < mb_strlen($string) / 2)
        return $string . $terminate;
    else
        return mb_substr($string, 0, $space) . $terminate;
}

Answer 2

Try this:

function truncate($string, $chars = 50, $terminator = ' …') {
    $cutPos = $chars - mb_strlen($terminator);
    $boundaryPos = mb_strrpos(mb_substr($string, 0, mb_strpos($string, ' ', $cutPos)), ' ');
    return mb_substr($string, 0, $boundaryPos === false ? $cutPos : $boundaryPos) . $terminator;
}

But you need to make sure that your internal encoding is properly set.