string htmlentities ([string $string ], [int $quote_style] , [string $charset])
quote_style
ENT_NOQUOTES    Will leave both double and single quotes unconverted.
ENT_QUOTES    Will convert both double and single quotes.
ENT_COMPAT    Will convert double-quotes and leave single-quotes alone.

EX:
     $strr = "A 'quote_value' is bold";
     echo htmlentities($strr)."
";
     echo htmlentities($strr, ENT_QUOTES);
?>
O/P:
A 'quote_value' is bold
A 'quote_value' is bold