How to replace spaces in strings with commas ',' in PHP_PHP Tutorial

/* 
* Replace spaces in keywords with ',' 
*/ 
public function emptyreplace($str) { 
$str = str_replace('　', ' ', $str); //Replace full-width spaces with half-width 
$str = str_replace(' ', ' ', $str); //Replace consecutive spaces with one 
$noe = false; //Whether encountered Characters that are not spaces
for ($i=0; $iif($noe && $str[$i]==' ') $str[$i] = ','; //If a character that is not a space appears before the current space
elseif($str[$i]!=' ') $noe=true; //Current This character is not a space. Define the $noe variable 
} 
return $str; 
} 
?>