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In order to compare for string equality, or if one string is alphabetically bigger than another, you can use the six string comparison operators. Here are the string operators together with the numerical operators they correspond too:

Notice that the string operators are built from the initials of their abbreviated names. (E.g: eq = equal, gt = greater than). Perl’s string comparison is case-sensitive. If you want a case insensitive string comparison, use the lc function to convert the strings to lowercase beforehand.

Do NOT throw exception in exception_handler function, if you do it like below, 

the error “Fatal error: Exception thrown without a stack frame in Unknown on line 

0” will occur

set_exception_handler('handle_exception');

function handle_exception($e)

{

    throw new Exception('throwed in handle_exception');

}

throw new Exception('error occur');

if you try-catch the Exception in exception_handler function, it will be ok, the below code will work well

set_exception_handler('handle_exception');

function handle_exception($e)

{

    try {

        throw new Exception('throwed in handle_exception');

    }

    catch (Exception $e) {

        die('catch exception in handle_exception function');

    }

}

throw new Exception('error occur');

Do NOT throw Exception in __destruct like below, or “Fatal error: Exception thrown

without a stack frame in Unknown on line 0” will occur.

class Test {

    function __construct () {}

    function __destruct() {

        throw new Exception('throwed in __destruct');

    }

}

$test = new Test();
but it will work well when try-catch it like below

class Test {

    function __construct () {}

    function __destruct() {

        try {

            throw new Exception('throwed in __destruct');

        }

        catch (Exception $e) {

            die('catch exception in __destruct');

        }


    }

}

$test = new Test();