Replacing the last occurrence of a character in a string

I have a little issue I'm trying to find a solution for.

Basically, imagine you have the following string:

    $string = 'Hello I am a string';

And you'd like it to end with something like the folowing:

    $string = 'Hello I am a&开发者_如何学JAVAnbsp;string';

Simply, replacing the last occurrence of a space, with a non-breaking space.

I'm doing this because I don't want the last word in a heading to be on its own. Simply because when it comes to headings:

 Hello I am a
 string

Doesn't look as good as

 Hello I am
 a string

How does one do such a thing?

Code from this example will do the trick:

// $subject is the original string
// $search is the thing you want to replace
// $replace is what you want to replace it with

substr_replace($subject, $replace, strrpos($subject, $search), strlen($search));

echo preg_replace('/\s(\S*)$/', ' $1', 'Hello I am a string');

Output

Hello I am a string

CodePad.

\s matches whitespace characters. To match a space explictly, put one in (and change \S to [^ ]).

This would do the trick:

$string = preg_replace('/([\s\S]+)\s(\w)$/','$1 $2',$string);

as per pounndifdef's answer, however i needed to decode the   HTML entity like so:

substr_replace($subject, html_entity_decode($replace), strrpos($subject, $search), strlen($search));

also worked using alex's answer:

preg_replace('/\s(\S*)$/', html_entity_decode(' ').'$1', 'Hello I am a string');

Use str_replace() like normal, but reverse the string first. Then, reverse it back.